High tobacco consumption lowers body weight: a Mendelian randomization study of the Copenhagen General Population Study

Post-diagnosis adiposity and colorectal cancer prognosis: A Global Cancer Update Programme (CUP Global) systematic literature review and meta-analysis

The adiposity influence on colorectal cancer prognosis remains poorly characterised. We performed a systematic review and meta-analysis on post-diagnosis adiposity measures (body mass index [BMI], waist circumference, waist-to-hip ratio, weight) or their changes and colorectal cancer outcomes. PubMed and Embase were searched through 28 February 2022. Random-effects meta-analyses were conducted when at least three studies had sufficient information. The quality of evidence was interpreted and graded by the Global Cancer Update Programme (CUP Global) independent Expert Committee on Cancer Survivorship and Expert Panel. We reviewed 124 observational studies (85 publications). Meta-analyses were possible for BMI and all-cause mortality, colorectal cancer-specific mortality, and cancer recurrence/disease-free survival. Non-linear meta-analysis indicated a reverse J-shaped association between BMI and colorectal cancer outcomes (nadir at BMI 28 kg/m2). The highest risk, relative to the nadir, was observed at both ends of the BMI distribution (18 and 38 kg/m2), namely 60% and 23% higher risk for all-cause mortality; 95% and 26% for colorectal cancer-specific mortality; and 37% and 24% for cancer recurrence/disease-free survival, respectively. The higher risk with low BMI was attenuated in secondary analyses of RCTs (compared to cohort studies), among studies with longer follow-up, and in women suggesting potential methodological limitations and/or altered physiological state. Descriptively synthesised studies on other adiposity-outcome associations of interest were limited in number and methodological quality. All the associations were graded as limited (likelihood of causality: no conclusion) due to potential methodological limitations (reverse causation, confounding, selection bias). Additional well-designed observational studies and interventional trials are needed to provide further clarification.

Estimating causality between smoking and abdominal obesity by Mendelian randomization

BACKGROUND AND AIMS

Smokers tend to have a lower body weight than non-smokers, but also more abdominal fat. It remains unclear whether or not the relationship between smoking and abdominal obesity is causal. Previous Mendelian randomization (MR) studies have investigated this relationship by relying upon a single genetic variant for smoking heaviness. This approach is sensitive to pleiotropic effects and may produce imprecise causal estimates. We aimed to estimate causality between smoking and abdominal obesity using multiple genetic instruments.

DESIGN

MR study using causal analysis using summary effect estimates (CAUSE) and latent heritable confounder MR (LHC-MR) methods that instrument smoking using genome-wide data, and also two-sample MR (2SMR) methods.

SETTING

Genome-wide association studies (GWAS) summary statistics from participants of European ancestry, obtained from the GWAS and Sequencing Consortium of Alcohol and Nicotine use (GSCAN), Genetic Investigation of Anthropometric Traits (GIANT) Consortium and the UK Biobank.

PARTICIPANTS

We used GWAS results for smoking initiation (n = 1 232 091), life-time smoking (n = 462 690) and smoking heaviness (n = 337 334) as exposure traits, and waist-hip ratio (WHR) and waist and hip circumferences (WC and HC) (n up to 697 734), with and without adjustment for body mass index (adjBMI), as outcome traits.

MEASUREMENTS

Smoking initiation, life-time smoking, smoking heaviness, WHR, WC, HC, WHRadjBMI, WCadjBMI and HCadjBMI.

FINDINGS

Both CAUSE and LHC-MR indicated a positive causal effect of smoking initiation on WHR (0.13 [95% confidence interval (CI) = 0.10, 0.16 and 0.49 (0.41, 0.57), respectively] and WHRadjBMI (0.07 (0.03, 0.10) and 0.31 (0.26, 0.37). Similarly, they indicated a positive causal effect of life-time smoking on WHR [0.35 (0.29, 0.41) and 0.44 (0.38, 0.51)] and WHRadjBMI [0.18 (0.13, 0.24) and 0.26 (0.20, 0.31)]. In follow-up analyses, smoking particularly increased visceral fat. There was no evidence of a mediating role by cortisol or sex hormones.

CONCLUSIONS

Smoking initiation and higher life-time smoking may lead to increased abdominal fat distribution. The increase in abdominal fat due to smoking is characterized by an increase in visceral fat. Thus, efforts to prevent and cease smoking can have the added benefit of reducing abdominal fat.

Lifestyle risk factors and all-cause and cause-specific mortality in the Mexico City prospective study: Assessing the influence of reverse causation

BACKGROUND

We examined the association between individual lifestyle risk factors with all-cause and cause-specific mortality.

METHODS

Prospective cohort study including 155,002 participants from the Mexico City Prospective Study. Cox regression models were used to estimate the association between individual lifestyle risk factors and all-cause and cause-specific mortality. Participants with prevalent diseases at baseline and participants who died during the first 2, 5, 10, and 15 years of follow-up were excluded to account for reverse causation.

RESULTS

27,469 people died during 18.3 years of follow-up years. Overweight and moderate alcohol consumption were inversely associated with all-cause mortality, while low physical activity and smoking were positively associated when all participants were included, regardless of prevalent disease or duration of follow-up. The direction of the association of overweight with all-cause mortality changed from inverse to positive after excluding the first 10 years of follow-up. Compared with normal weight, the hazard ratio (95 % confidence interval) was 1.17 (1.13,1.22) for obesity after excluding those who died in the first 5 years of follow-up and 1.71 (1.59,1.84) after excluding the first 15 years of follow-up. The magnitude of the association of alcohol intake, low physical activity, and smoking with mortality attenuated, whereas for fruits and vegetables increased, after excluding longer periods of follow-up.

LIMITATIONS

The data were collected exclusively in Mexico City; lifestyle risk factors were self-reported and thus prone to misclassification bias.

CONCLUSIONS

Reverse causation may influence both the magnitude and the direction of the associations between lifestyle risk factors and mortality.

Comparison of metabolic syndrome prevalence and characteristics using five different definitions in China: a population-based retrospective study

Background

Metabolic syndrome (MetS) is on the rise in developing countries and is characterized by a series of indications of metabolic disturbance. However, the prevalence of MetS varies under different definitions. The study aimed to compare five definitions of MetS in the China adult population, to explore their prevalence, characteristics and agreement.

Methods

The data for the retrospective study came from the China Health and Retirement Longitudinal Study (CHARLS), consisting of 9,588 participants (≥45). MetS definitions from International Diabetes Federation (IDF) (2006), National Cholesterol Education Program Adult Treatment Panel III (ATPIII) (2005), National Cholesterol Education Program Adult Treatment Panel III (ATPIII) (2001), Chinese Diabetes society (CDS) (2004) and the World Health Organization (WHO) (1999). We used binary and multivariable logistic analysis to explore factors connected with MetS.

Results

The five definitions of MetS led to different prevalence of MetS:34.52% by IDF (2006), 38.63% by ATP (2005), 25.94% by ATP (2001), 26.31% by CDS (2004), 21.57% by WHO (1999). According to the definition of IDF (2006) (22.32% vs. 45.06%), ATPIII (2005) definition (27.99% vs. 47.82%), ATPIII (2001) definition (15.37% vs. 35.07%), CDS (2004) definition (19.96% vs. 31.80%), and WHO (1999) definition (17.44% vs. 25.14%), the prevalence of MetS in men was low but in women was high. The agreement between the five definitions for men was good except for the IDF (2006) definition and ATPIII (2001) definition (kappa = 0.51), with kappa values from 0.64 to 0.85. For women, the agreement between the five definitions was good ranging from 0.67 to 0.95, however, except for the definition of CDS (2004) and the definition of IDF (2006) (kappa = 0.44), the definition of WHO (1999) and the definition of IDF (2006) (kappa = 0.55), and the definition of WHO (1999) and the definition of ATPIII (2005) (kappa = 0.54). Binary logistic analysis indicated that although the impact and relevance varied by sex and definition, age, education, marital status, current residence, current smoking, alcohol using, taking activities and number of chronic diseases were factors connected to MetS.

Conclusion

the prevalence and characteristics of the five definitions of MetS are different in the Chinese population. Therefore, it is vital to use the same definition for a country to diagnose MetS. On the other side, a lower prevalence in men than in women and the consistency of five MetS definitions are good in men but relatively poor in women.

General or Central Obesity and Mortality Among US Hispanic and Latino Adults

Importance

The Hispanic and Latino population is the second largest ethnic group in the US, but associations of obesity parameters with mortality in this population remain unclear.

Objective

To investigate the associations of general and central obesity with mortality among US Hispanic and Latino adults.

Design, Setting, and Participants

The Hispanic Community Health Study/Study of Latinos is an ongoing, multicenter, population-based cohort study with a multistage probability sampling method performed in Hispanic and Latino adults aged 18 to 74 years with a baseline between January 1, 2008, and December 31, 2011. Active follow-up for this analyses extended from baseline through February 17, 2022. All analyses accounted for complex survey design (ie, stratification and clustering) and sampling weights to generate estimates representing the noninstitutionalized, 18- to 74-year-old Hispanic or Latino populations from selected communities.

Exposures

Body mass index (BMI; calculated as weight in kilograms divided by height in meters squared), body fat percentage, waist circumference (WC), and waist to hip ratio (WHR).

Main Outcome and Measure

Deaths were ascertained via death certificates, the National Death Index, and active follow-up.

Results

Of 15 773 adults (mean [SE] age, 40.9 [0.3] years; 52.8% female), 686 deaths occurred during a median (IQR) follow-up of 10.0 (9.9-10.2) years. When adjusting for sociodemographic, lifestyle, and family history covariates, hazard ratios (HRs) for mortality were 1.55 (95% CI, 1.08-2.22) for a BMI of 35.0 or greater vs 18.5 to 24.9, 1.22 (95% CI, 0.92-1.64) for the highest vs lowest body fat percentage groups (defined according to sex-, age-, and Hispanic or Latino background-specific BMI distribution), 1.35 (95% CI, 0.98-1.85) for WC greater than 102 cm (men) or 88 cm (women) vs 94 cm (men) or 80 cm (women) or less, and 1.91 (95% CI, 1.28-2.86) for WHR of 0.90 (men) or 0.85 (women) or greater vs less than 0.90 (men) or 0.85 (women). Only WHR was associated with mortality with additional adjustment for major comorbidities (HR, 1.75; 95% CI, 1.17-2.62). The association of WHR with mortality was stronger among women compared with men (P = .03 for interaction), and the association between BMI and mortality was stronger among men (P = .02 for interaction). The positive association between severe obesity (BMI ≥ 35.0) and mortality was observed only among adults with WHR of 0.90 (men) or 0.85 (women) or greater but not among those with WHR below 0.90 (men) or 0.85 (women) (P = .005 for interaction) who had greater hip circumference.

Conclusions and Relevance

In this cohort of US Hispanic and Latino adults, WHR was independently associated with higher all-cause mortality regardless of BMI and prevalent comorbidities. These findings suggest that prioritizing clinical screening and intervention for WHR in this population may be an important public health strategy, with sex-specific strategies potentially being needed.

Association of serum leptin and ghrelin levels with smoking status on body weight: a systematic review and meta-analysis

Background and aims

Smoking cigarettes is a major global health problem that affects appetite and weight. The aim of this systematic review was to determine how smoking affected plasma leptin and ghrelin levels.

Methods

A comprehensive search of PubMed, Scopus, Web of Science, and Ovid was conducted using a well-established methodology to gather all related publications.

Results

A total of 40 studies were included in the analysis of 11,336 patients. The overall effect showed a with a mean difference (MD) of -1.92[95%CI; -2.63: -1.20] and p = 0.00001. Subgroup analysis by study design revealed significant differences as well, but with high heterogeneity within the subgroups (I2 of 82.3%). Subgroup by sex showed that there was a significant difference in mean difference between the smoking and non-smoking groups for males (MD = -5.75[95% CI; -8.73: -2.77], p = 0.0002) but not for females (MD = -3.04[95% CI; -6.6:0.54], p = 0.10). Healthy, pregnant, diabetic and CVD subgroups found significant differences in the healthy (MD = -1.74[95% CI; -03.13: -0.35], p = 0.01) and diabetic (MD = -7.69[95% CI, -1.64: -0.73], p = 0.03). subgroups, but not in the pregnant or cardiovascular disease subgroups. On the other hand, the meta-analysis found no statistically significant difference in Ghrelin serum concentration between smokers and non-smokers (MD = 0.52[95% CI, -0.60:1.63], p = 0.36) and observed heterogeneity in the studies (I2 = 68%).

Conclusion

This study demonstrates a correlation between smoking and serum leptin/ghrelin levels, which explains smoking's effect on body weight.

Systematic review registration

https://www.crd.york.ac.uk/ prospero/display_record.php, identifier (Record ID=326680).

Causal effects from tobacco smoking initiation on obesity-related traits: a Mendelian randomization study

BACKGROUND

There is a widespread notion that tobacco smoking controls weight based on the appetite suppressive effect of nicotine. However, the causal relationship between smoking initiation and obesity-related traits in the general population are unclear.

METHODS

This Mendelian randomization analysis utilized 378 genetic variants associated with tobacco smoking initiation (usually in adolescence or young adulthood) identified in a genome-wide association study (meta-analysis) of 1.2 million individuals. Outcome data for body mass index, waist circumference, hip circumference, and waist-to-hip ratio were extracted from the 337,138 white British-ancestry UK Biobank participants aged 40-69 years. Replication analyses were performed for genome-wide association study meta-analysis for body mass index, including the GERA/GIANT data including 364,487 samples from mostly European individuals. In addition, summary-level Mendelian randomization by inverse variance weighted method and pleiotropy-robust Mendelian randomization methods, including median-based and MR-Egger regression, was performed.

RESULTS

Summary-level Mendelian randomization analysis indicated that genetically predicted smoking initiation is causally linked to higher body mass index [+0.28 (0.18-0.38) kg/m2], waist circumference [+0.88 (0.66-1.10) cm], hip circumference [+0.40 (0.23-0.57) cm], and waist-to-hip ratio [+0.006 (0.005-0.007)]. These results were consistent with those of the pleiotropy-robust Mendelian randomization analysis. Additionally, in replication analysis, genetically predicted smoking initiation was significantly associated with a higher body mass index [+0.03 (0.01, 0.05] kg/m2).

CONCLUSION

Tobacco initiation may lead to worse obesity-related traits in the general 40- to 69-year-old individuals. Therefore, tobacco-use initiation as a long-term weight-control measure should be discouraged.

Tobacco smoke exacerbates Filifactor alocis pathogenicity

AIM

Filifactor alocis has recently emerged as a periodontal pathobiont that appears to thrive in the oral cavity of smokers. We hypothesized that identification of smoke-responsive F. alocis genes would provide insight into adaptive strategies and that cigarette smoke would enhance F. alocis pathogenesis in vivo.

MATERIALS AND METHODS

F. alocis was grown in vitro and cigarette smoke extract-responsive genes determined by RNAseq. Mice were exposed, or not, to mainstream 1R6F research cigarette smoke and infected with F. alocis, or not, in an acute ligature model of periodontitis. Key clinical, infectious, and immune data were collected.

RESULTS

In culture, F. alocis growth was unaffected by smoke conditioning and only a small number of genes were specifically regulated by smoke exposure. Reduced murine mass, differences in F. alocis-cognizant antibody production, and altered immune profiles as well as altered alveolar bone loss were all attributable to smoke exposure and/or F. alocis infection in vivo.

CONCLUSIONS

F. alocis is well-adapted to tobacco-rich conditions and its pathogenesis is enhanced by tobacco smoke exposure. A smoke-exposed ligature model of periodontitis shows promise as a tool with which to further unravel mechanisms underlying tobacco-enhanced, bacteria-induced disease.

How does childhood maltreatment influence cardiovascular disease? A sequential causal mediation analysis

BACKGROUND

Childhood maltreatment has been consistently associated with cardiovascular disease (CVD). However, the mechanisms of this relationship are not yet fully understood. We explored the relative contribution of anxiety/depression, smoking, body mass index (BMI) and inflammation (C-reactive protein, CRP) to the association between childhood maltreatment and CVD in men and women aged 40-69 years in the UK.

METHODS

We used data from 40 596 men and 59 511 women from UK Biobank. To estimate the indirect effects of childhood maltreatment (physical, sexual and emotional abuse, and emotional and physical neglect) on incident CVD via each of the mediators, we applied a sequential mediation approach.

RESULTS

All forms of maltreatment were associated with increased CVD risk [hazard ratios (HRs) ranging from 1.09 to 1.27]. Together, anxiety/depression, smoking, BMI and inflammation (indexed by CRP) mediated 26-90% of the association between childhood maltreatment and CVD, and the contribution of these mediators differed by type of maltreatment and sex. Anxiety/depression mediated the largest proportion of the association of sexual abuse, emotional abuse and emotional neglect with CVD (accounting for 16-43% of the total effect), especially in women. In men, BMI contributed the most to the indirect effect of associations of physical abuse and physical neglect with CVD; in women, anxiety/depression and BMI had similar contributions.

CONCLUSIONS

These findings add to the understanding of how childhood maltreatment affects CVD risk and identify modifiable mediating factors that could potentially reduce the burden of CVD in people exposed to maltreatment in early life.

Likelihood-based Mendelian randomization analysis with automated instrument selection and horizontal pleiotropic modeling

Mendelian randomization (MR) is a common tool for identifying causal risk factors underlying diseases. Here, we present a method, MR with automated instrument determination (MRAID), for effective MR analysis. MRAID borrows ideas from fine-mapping analysis to model an initial set of candidate single-nucleotide polymorphisms that are in potentially high linkage disequilibrium with each other and automatically selects among them the suitable instruments for causal inference. MRAID also explicitly models both uncorrelated and correlated horizontal pleiotropic effects that are widespread for complex trait analysis. MRAID achieves both tasks through a joint likelihood framework and relies on a scalable sampling-based algorithm to compute calibrated P values. Comprehensive and realistic simulations show that MRAID can provide calibrated type I error control and reduce false positives while being more powerful than existing approaches. We illustrate the benefits of MRAID for an MR screening analysis across 645 trait pairs in U.K. Biobank, identifying multiple lifestyle causal risk factors of cardiovascular disease-related traits.

Association between Thyroid Cancer and Breast Cancer: Two Longitudinal Follow-Up Studies Using a National Health Screening Cohort

Background: The purpose of this study was to evaluate the association between thyroid cancer and breast cancer. Methods: Data from the Korean National Health Insurance Service-Health Screening Cohort were collected from 2002 to 2013. In study I, 3949 thyroid cancer participants were 1:4 matched with 15,796 control I participants, and hazard ratios (HRs) with 95% confidence intervals (CIs) for breast cancer were evaluated using a stratified Cox proportional hazard model. In study II, 3308 breast cancer participants were 1:4 matched with 13,232 control II participants, and HRs with 95% CIs for thyroid cancer were assessed in the same way as in study I. In the subgroup analyses, associations were analyzed according to radioactive iodine (RAI) treatment and age (<60 years old and ≥60 years old). Results: The adjusted HR for breast cancer in the thyroid cancer group was 1.64 (95% CI = 1.13–2.39, p = 0.010). The adjusted HR for thyroid cancer in the breast cancer group was 1.91 (95% CI = 1.47–2.49, p < 0.001). In the subgroup analyses, the groups that were older and not treated with RAI treatment showed consistent results in study I, and the younger and older groups showed consistent results in study II. Conclusions: Based on this cohort study, breast and thyroid cancer have a reciprocal positive association.

Cannabis use and obesity-traits: A Mendelian randomization study

BACKGROUND

Observational studies suggested that cannabis use is associated with decreased body fatness; however, observational studies are subject to confounding, making causal inference and determining the direction of these associations difficult. We performed Mendelian randomization (MR) using summary statistics from genome-wide association studies (GWAS) to investigate the potential causal association of cannabis use and obesity-related traits.

METHODS

We used 51 single nucleotide polymorphisms (SNPs) associated with lifetime cannabis use at P 1<×  10^-5 from a GWAS of 184,765 individuals of European descent and 27 SNPs genome-wide associated with cannabis use disorder as instrumental variables. The GWAS for body mass index (BMI) was derived from a meta-analysis of up to 322,154 individuals, and the GWAS for waist circumference (WC) and waist-hip ratio (WHR) included 210,088 participants.

RESULTS

MR showed that lifetime cannabis use (beta = - 0.018, 95 % confidence interval (CI): - 0.05-0.015; P-value = 0.279, Q-value = 0.279) and cannabis use disorder (beta = 0.023, 95 % CI: 0.023-0.045; P-value = 0.034, Q-value = 0.092) were not associated with BMI. Considering WC and WHR as indicators of obesity, our findings did not support a causal association. Leave-one out analyses and pleiotropy-robust methods did not indicate bias in any of the estimates.

CONCLUSIONS

Overall, the MR study provides little evidence that cannabis influences obesity related traits.

Risk of ulcerative colitis and Crohn's disease in smokers lacks causal evidence

Smoking has been associated with opposing risks of ulcerative colitis and Crohn's disease. Whether these observational associations reflect actual causal associations, confounding, or reverse causation is unclear. Using a Mendelian randomization approach, we tested the hypothesis that smoking protects against ulcerative colitis and is a cause of Crohn's disease. We included 118,683 white Danes aged ≥ 20 from the Copenhagen General Population Study (2003-2015) and the Copenhagen City Heart Study (1991-94 and 2001-03). During follow-up until 2018, we investigated the association of smoking and CHRNA3 rs1051730, where the T-allele is strongly associated with nicotine dependence, with risk of ulcerative colitis and Crohn's disease. We identified 1312 cases of ulcerative colitis and 671 cases of Crohn's disease. Compared to never-smokers, multivariable adjusted hazard ratios (HRs) for ulcerative colitis were 1.69(95% confidence interval [CI] 1.32-2.15) in former smokers and 2.27(1.74-2.96) in current smokers. Corresponding HRs for Crohn's disease were 1.31(0.93-1.84) and 1.93(1.34-2.78), respectively. Among ever-smokers when compared to non-carriers of the CHRNA3 rs1051730 T-allele, age and sex adjusted HRs for risk of ulcerative colitis were 1.03(95%CI 0.89-1.18) in heterozygotes and 0.91(0.72-1.16) in homozygotes. Corresponding HRs for Crohn's disease were 1.05(0.87-1.28) and 1.02(0.74-1.41), respectively. In a meta-analysis combined with UK Biobank, there was no evidence that CHRNA3 rs1051730 was associated with risk of ulcerative colitis or Crohn's disease. In conclusion, current versus never-smoking was associated with unexpected 2.3-fold risk of ulcerative colitis and expected 1.9-fold risk of Crohn's disease in prospective analyses; however, genetic evidence of lifelong increased smoking intensity did not support causal relationships.

Distributions of serum thyroid-stimulating hormone in 2020 thyroid disease-free adults from areas with different iodine levels: a cross-sectional survey in China

PURPOSE

The aim of the present study was to describe the distributions of serum thyroid- stimulating hormone (TSH) levels in thyroid disease-free adults from areas with different iodine levels in China. Meanwhile, we aimed to evaluate the influence of age and gender on the distribution of TSH, assess the relationship between concentrations of TSH and free thyroxine (FT₄), and analyze the factors that may affect TSH levels.

METHODS

2020 adults were included from April 2016 to June 2019. Urinary iodine concentration, serum iodine concentration, serum TSH, FT₄, free triiodothyronine, thyroid peroxidase antibodies and thyroglobulin antibodies were measured, and thyroid ultrasonography was performed.

RESULTS

The median of TSH in iodine-fortification areas (IFA), iodine-adequate areas (IAA), iodine-excessive areas (IEA) were 2.32, 2.11 and 2.34 mIU/L, respectively. Serum TSH concentrations were significantly higher in IFA and IEA than that in IAA (p = 0.005 and < 0.0001). The TSH values of most adults were distributed within the range of 1.01-3.00 mIU/L with the same trend in three groups. In our study, TSH levels did not change with age, and the TSH level of females was higher than that of males (p < 0.0001). There was a negative correlation between FT₄ and TSH in IAA (r = - 0.160, p < 0.0001) and IEA (r = - 0.177, p < 0.0001), but there was no correlation between FT₄ and TSH in IFA (r = - 0.046, p = 0.370). BMI, smoking status, education levels, and marital status were associated with TSH.

CONCLUSION

Our study provides a basis for establishing the reference intervals of TSH in different iodine level areas.

Causal relationships between body mass index, smoking and lung cancer: Univariable and multivariable Mendelian randomization

At the time of cancer diagnosis, body mass index (BMI) is inversely correlated with lung cancer risk, which may reflect reverse causality and confounding due to smoking behavior. We used two-sample univariable and multivariable Mendelian randomization (MR) to estimate causal relationships of BMI and smoking behaviors on lung cancer and histological subtypes based on an aggregated genome-wide association studies (GWASs) analysis of lung cancer in 29 266 cases and 56 450 controls. We observed a positive causal effect for high BMI on occurrence of small-cell lung cancer (odds ratio (OR) = 1.60, 95% confidence interval (CI) = 1.24-2.06, P = 2.70 × 10-4 ). After adjustment of smoking behaviors using multivariable Mendelian randomization (MVMR), a direct causal effect on small cell lung cancer (ORMVMR = 1.28, 95% CI = 1.06-1.55, PMVMR = .011), and an inverse effect on lung adenocarcinoma (ORMVMR = 0.86, 95% CI = 0.77-0.96, PMVMR = .008) were observed. A weak increased risk of lung squamous cell carcinoma was observed for higher BMI in univariable Mendelian randomization (UVMR) analysis (ORUVMR = 1.19, 95% CI = 1.01-1.40, PUVMR = .036), but this effect disappeared after adjustment of smoking (ORMVMR = 1.02, 95% CI = 0.90-1.16, PMVMR = .746). These results highlight the histology-specific impact of BMI on lung carcinogenesis and imply mediator role of smoking behaviors in the association between BMI and lung cancer.

Inference of a causal relation between low-density lipoprotein cholesterol and hypertension using mendelian randomization analysis

BACKGROUND

It is known in some studies that higher the LDL-C, the greater the risk of developing cardiovascular disease. However, studies of the causal effects between LDL-C and hypertension are limited by their observational study design, and genetic epidemiology studies of associations between LDL-C and hypertension are lacking, as are studies using data for Koreans. In this study, we confirmed the causal effect of LDL-C on hypertension using Korean chip data.

METHOD

The epidemiology and genotype data were collected from the Korean Genome and Epidemiology Study conducted by the Korea National Institute of Health and covered 20,701 subjects. Single-nucleotide polymorphisms associated with LDL-C were selected (p-value < 5 × 10^- 8) from the Global Lipids Genetics Consortium database, and Mendelian randomization analysis (MRA) was performed with counted genetic risk scores and weighted genetic risk scores (WGRSs) for 24 single-nucleotide polymorphisms.

RESULT

The assumptions for MRA were statistically confirmed, and WGRSs showed a strong association with LDL-C. Interestingly, while the relationship between LDL-C and hypertension was not statistically significant in the observational study, MRA study demonstrated that the risk of hypertension increased as LDL-C increased in both men and women.

CONCLUSIONS

The results of this study confirmed that the relationship between LDL-C and hypertension is greatly influenced by genetic information.

Cigarette smoking exposure breaks the homeostasis of cholesterol and bile acid metabolism and induces gut microbiota dysbiosis in mice with different diets

Exposure of humans to second-hand smoking (SHS) increases glucose and lipid metabolic disorders. The link of hepatic metabolic dysfunction to environmental cigarette smoking has been noticed, but the related mechanism is still unclear. C57BL/6 mice with normal food diet (NFD) or high fat diet (HFD) were exposed to 15 min cigarette smoking twice a day in a 0.038 m³ box for 4 weeks, and the concentration of nicotine in the air of the box was 21.05 mg/m³ during the smoke exposure. Liver tissues and serum were collected for gene expression and biochemistry test. The fecal microbiota was also checked through 16S rDNA sequences. Cigarette smoking exposure increased the accumulation of total cholesterol (TC) in liver, and the expression of cholesterol synthesis-related genes was upregulated. The expression of CYP8B1 protein was significantly down-regulated, and the ratio of cholic acid (CA) to chenodeoxycholic acid (CDCA) was significantly reduced in the liver of mice exposed to cigarette smoking especially for HFD group. Cigarette smoking exposure caused insulin resistance in the liver of mice with HFD. The composition of the gut microbiota was altered with the exposure of cigarette smoking, and the change of the distribution of primary bile acids might be one of the reasons. It was concluded that cigarette smoking would break the homeostasis of cholesterol and bile acids metabolism and changed the composition of gut microbiota. Our discoveries confirmed that smoking bans are important for the public health.

Genetics of Smoking and Risk of Atherosclerotic Cardiovascular Diseases: A Mendelian Randomization Study

IMPORTANCE

Smoking is associated with atherosclerotic cardiovascular disease, but the relative contribution to each subtype (coronary artery disease [CAD], peripheral artery disease [PAD], and large-artery stroke) remains less well understood.

OBJECTIVE

To determine the association between genetic liability to smoking and risk of CAD, PAD, and large-artery stroke.

DESIGN, SETTING, AND PARTICIPANTS

Mendelian randomization study using summary statistics from genome-wide associations of smoking (UK Biobank; up to 462 690 individuals), CAD (Coronary Artery Disease Genome Wide Replication and Meta-analysis plus the Coronary Artery Disease Genetics Consortium; up to 60 801 cases, 123 504 controls), PAD (VA Million Veteran Program; up to 24 009 cases, 150 983 controls), and large-artery stroke (MEGASTROKE; up to 4373 cases, 406 111 controls). This study was conducted using summary statistic data from large, previously described cohorts. Review of those publications does not reveal the total recruitment dates for those cohorts. Data analyses were conducted from August 2019 to June 2020.

EXPOSURES

Genetic liability to smoking (as proxied by genetic variants associated with lifetime smoking index).

MAIN OUTCOMES AND MEASURES

Risk (odds ratios [ORs]) of CAD, PAD, and large-artery stroke.

RESULTS

Genetic liability to smoking was associated with increased risk of PAD (OR, 2.13; 95% CI, 1.78-2.56; P = 3.6 × 10-16), CAD (OR, 1.48; 95% CI, 1.25-1.75; P = 4.4 × 10-6), and stroke (OR, 1.40; 95% CI, 1.02-1.92; P = .04). Genetic liability to smoking was associated with greater risk of PAD than risk of large-artery stroke (ratio of ORs, 1.52; 95% CI, 1.05-2.19; P = .02) or CAD (ratio of ORs, 1.44; 95% CI, 1.12-1.84; P = .004). The association between genetic liability to smoking and atherosclerotic cardiovascular diseases remained independent from the effects of smoking on traditional cardiovascular risk factors.

CONCLUSIONS AND RELEVANCE

In this mendelian randomization analysis of data from large studies of atherosclerotic cardiovascular diseases, genetic liability to smoking was a strong risk factor for CAD, PAD, and stroke, although the estimated association was strongest between smoking and PAD. The association between smoking and atherosclerotic cardiovascular disease was independent of traditional cardiovascular risk factors.

Deciphering the Irregular Risk of Stroke Increased by Obesity Classes: A Stratified Mendelian Randomization Study

BACKGROUND

To investigate the relationship between different classes of obesity and stroke, we conducted a stratified Mendelian randomization (MR) study.

METHODS

The body mass index (BMI) data of 263,407 Europeans with three classes of obesity (obesity class I, 30 kg/m² ≤ BMI < 35 kg/m²; obesity class II, 35 kg/m² ≤ BMI < 40 kg/m²; obesity class III, 40 kg/m² ≤ BMI) were extracted from the Genetic Investigation of ANthropometric Traits (GIANT) consortium. Summary-level data of stroke and its subtypes [ischemic stroke (IS) and intracerebral hemorrhage (ICH)] were obtained from the genome-wide association study (GWAS) meta-analysis, which was performed by the MEGASTROKE consortium. MR methods were used to identify the causal relationships.

RESULTS

The MR analysis revealed that both obesity class I [odds ratio (OR) = 1.08, 95% CI: 1.05-1.12, p = 1.0 × 10^-5] and obesity class II (OR = 1.06, 95% CI: 1.03-1.09, p = 1 × 10^-4) were significantly positively related to IS, while obesity class III was not (OR = 1.01, 95% CI: 0.96-1.06, p = 0.65). In contrast to IS, there was no class of obesity associated with ICH risk. Further examination of the relationship between obesity classification and IS subtypes revealed that certain degrees of obesity were related to large artery stroke (LAS) (OR = 1.14, 95% CI: 1.04-1.24, p = 2.8 × 10^-3 for class I; OR = 1.08, 95% CI: 1.01-1.16, p = 0.002 for class II) and cardioembolic stroke (CES) (OR = 1.11, 95% CI: 1.02-1.20, p = 0.02 for class I; OR = 1.08, 95% CI: 1.02-1.15, p = 0.007 for class II).

CONCLUSIONS

A higher risk of IS, but not ICH, could be linked to obesity classes I and II. A strong association between LAS and CES and obesity was observed among all IS subtypes in the obese population.

Vaping for weight control: Findings from a qualitative study

INTRODUCTION

Smokers have expressed concern about weight gain once they stop smoking and weight gain is a risk factor associated with smoking relapse. Nicotine in e-cigarettes, as well as vaping behaviour, may support smoking cessation by reducing weight gain. This study explored the factors that influence attitudes towards, and awareness of, e-cigarettes and weight control post smoking cessation.

METHODS

Qualitative study involving focus groups with adults in the UK (n = 58) who were either exclusive vapers or dual users.

RESULTS

There was limited awareness and/or inclination to vape to prevent weight gain after stopping smoking. Reasons for this centred on: the health gains of stopping smoking outweighing any potential weight gain; a lack of understanding of the appetite supressing effects of nicotine; a belief that vaping could not suppress appetite like a cigarette and could result in craving for certain flavours; concerns about the longer-term effects of e-cigarettes on health and the ethics of promoting vaping as way to support smoking cessation by limiting weight gain, especially for young women.

CONCLUSION

Participants in this study do not appear inclined to use e-cigarettes to prevent weight gain after smoking cessation. There is a lack of understanding about why nicotine might help prevent weight gain and a concern that e-cigarette flavours could provoke cravings and that vaping may be unsafe in the long-term.

Smoking Reduces Plasma Bilirubin: Observational and Genetic Analyses in the Copenhagen General Population Study

INTRODUCTION

Observational studies have found lower concentrations of plasma bilirubin in current smokers compared with former and never smokers. However, whether there is a causal relationship between smoking and bilirubin is unknown. In a Mendelian randomization analysis, we tested the hypothesis that higher tobacco consumption is causally associated with lower concentrations of plasma bilirubin.

METHODS

We genotyped 103 557 individuals aged 20-100 years from the Copenhagen General Population Study for the CHRNA3 rs1051730 genotype, known to be associated with higher tobacco consumption. Tobacco consumption was defined as daily and cumulative tobacco consumption.

RESULTS

In observational multivariable-adjusted analyses, a 10 g/day higher daily tobacco consumption was associated with a 0.28 µmol/L (95% confidence interval = 0.20 to 0.35) lower concentration of plasma bilirubin in current smokers, and a 10 pack-year higher cumulative tobacco consumption was associated with a 0.19 µmol/L (0.17 to 0.21) lower concentration of plasma bilirubin in former and current smokers. Using the CHRNA3 rs1051730 genotype as a proxy for daily and cumulative tobacco consumption, the difference in plasma bilirubin per T-allele was -0.12 µmol/L (-0.23 to -0.002) in current smokers and -0.09 µmol/L (-0.15 to -0.01) in current and former smokers combined. Furthermore, observationally bilirubin concentrations increased with time from smoking cessation in former smokers.

CONCLUSION

Higher daily and cumulative tobacco consumption were associated with lower concentrations of plasma bilirubin in observational and genetic analyses, suggesting that the association is causal.

IMPLICATIONS

Our results are compatible with two possible interpretations of previous observational studies, either that bilirubin is a mediator of smoking-induced respiratory disease or that the association between plasma bilirubin and respiratory disease stems from residual confounding because of smoking. Future studies should examine whether bilirubin is a causal risk factor for respiratory disease, or merely a marker of smoking status.

Smoking, Systemic Inflammation, and Airflow Limitation: A Mendelian Randomization Analysis of 98 085 Individuals From the General Population

INTRODUCTION

Smoking is associated with systemic and local inflammation in the lungs. Furthermore, in chronic obstructive pulmonary disease, which is often caused by smoking, there is often systemic inflammation that is linked to lung function impairment. However, the causal pathways linking smoking, systemic inflammation, and airflow limitation are still unknown. We tested whether higher tobacco consumption is associated with higher systemic inflammation, observationally and genetically and whether genetically higher systemic inflammation is associated with airflow limitation.

METHODS

We included 98 085 individuals aged 20-100 years from the Copenhagen General Population Study; 36589 were former smokers and 16172 were current smokers. CHRNA3 rs1051730 genotype was used as a proxy for higher tobacco consumption and the IL6R rs2228145 genotype was used for higher systemic inflammation. Airflow limitation was defined as forced expiratory volume in 1 s (FEV1)/forced vital capacity (FVC) <70%.

RESULTS

Difference in plasma level of C-reactive protein was 4.8% (95% CI = 4.4% to 5.2%) per 10 pack-year increase and 1.6% (95% CI = 0.4% to 2.8%) per T allele. Corresponding differences were 1.2% (95% CI = 1.1% to 1.3%) and 0.5% (95% CI = 0.3% to 0.8%) for fibrinogen, 1.2% (95% CI = 1.2% to 1.3%) and 0.7% (95% CI = 0.5% to 1.0%) for α1-antitrypsin, 2.0% (95% CI = 1.8% to 2.1%) and 0.7% (95% CI = 0.4% to 1.1%) for leukocytes, 1.9% (95% CI = 1.8% to 2.1%) and 0.8% (95% CI = 0.4% to 1.2%) for neutrophils, and 0.8% (95% CI = 0.7% to 1.0%) and 0.4% (95% CI = 0.1% to 0.7%) for thrombocytes. The differences in these levels were lower for former smokers compared with current smokers. The IL6R rs2228145 genotype was associated with higher plasma acute-phase reactants but not with airflow limitation. Compared with the C/C genotype, the odds ratio for airflow limitation was 0.95 (95% CI = 0.89 to 1.02) for A/C genotype and 0.94 (95% CI = 0.87 to 1.01) for A/A genotype.

CONCLUSIONS

Higher tobacco consumption is associated with higher systemic inflammation both genetically and observationally, whereas systemic inflammation was not associated with airflow limitation genetically.

IMPLICATIONS

The association between higher tobacco consumption and higher systemic inflammation may be causal, and the association is stronger among current smokers compared to former smokers, indicating that smoking cessation may reduce the effects of smoking on systemic inflammation. Systemic inflammation does not seem to be a causal driver in development of airflow limitation. These findings can help to understand the pathogenic effects of smoking and the interplay between smoking, systemic inflammation, and airflow limitation and hence development and progression of chronic obstructive pulmonary disease.

Impact of body mass index and metabolically unhealthy status on mortality in the Japanese general population: The JMS cohort study

This study aimed to investigate the associations of body mass index (BMI) and metabolically unhealthy weight with all-cause mortality, cardiovascular disease (CVD) mortality, and cancer mortality as well as the effect of age on the associations. This prospective study enrolled Japanese individuals in the general population. Participants were divided into eight phenotypes according to the BMI classification and metabolic status. Hazard ratios (HRs) and 95% confidence intervals (CIs) were calculated using a Cox regression hazard model. In total, 10,824 individuals with a mean age of 55.3 years were evaluated. During a mean follow-up of 18.4 years (198,776 person-years), 2,274 participants died. Among the metabolically unhealthy, the association between BMI and mortality was J-shaped after adjustment for various confounders (multivariable HR [95% CI] for all-cause mortality: underweight, 2.0 [1.5-2.7]; obesity 2.8 [2.1-3.6]). The association remained the same in metabolically unhealthy participants aged <65 years and ≥65 years. The results were compatible in the analyses restricted to subjects who never smoked. Regardless of age, metabolically unhealthy underweight (MUHU) have approximately a 3-fold higher risk of CVD mortality, compared with metabolically healthy normal weight. Not only metabolically unhealthy obesity, but also MUHU was strongly associated with an increased risk of mortality. More attention should be given to the health issues of metabolically unhealthy participants without obesity, particularly those with MUHU.

MR-pheWAS with stratification and interaction: Searching for the causal effects of smoking heaviness identified an effect on facial aging

Mendelian randomization (MR) is an established approach to evaluate the effect of an exposure on an outcome. The gene-by-environment (GxE) study design can be used to determine whether the genetic instrument affects the outcome through pathways other than via the exposure of interest (horizontal pleiotropy). MR phenome-wide association studies (MR-pheWAS) search for the effects of an exposure, and can be conducted in UK Biobank using the PHESANT package. In this proof-of-principle study, we introduce the novel GxE MR-pheWAS approach, that combines MR-pheWAS with the use of GxE interactions. This method aims to identify the presence of effects of an exposure while simultaneously investigating horizontal pleiotropy. We systematically test for the presence of causal effects of smoking heaviness-stratifying on smoking status (ever versus never)-as an exemplar. If a genetic variant is associated with smoking heaviness (but not smoking initiation), and this variant affects an outcome (at least partially) via tobacco intake, we would expect the effect of the variant on the outcome to differ in ever versus never smokers. We used PHESANT to test for the presence of effects of smoking heaviness, instrumented by genetic variant rs16969968, among never and ever smokers respectively, in UK Biobank. We ranked results by the strength of interaction between ever and never smokers. We replicated previously established effects of smoking heaviness, including detrimental effects on lung function. Novel results included a detrimental effect of heavier smoking on facial aging. We have demonstrated how GxE MR-pheWAS can be used to identify potential effects of an exposure, while simultaneously assessing whether results may be biased by horizontal pleiotropy.

Vaping for weight control: A cross-sectional population study in England

INTRODUCTION

Concern about weight gain is a barrier to smoking cessation. E-cigarettes may help quitters to control their weight through continued exposure to the appetite-suppressant effects of nicotine and behavioural aspects of vaping. This study explored the views and practices of smokers, ex-smokers and current e-cigarette users relating to vaping and weight control.

METHODS

Cross-sectional survey of past-year smokers (n = 1320), current smokers (n = 1240) and current e-cigarette users (n = 394) in England, conducted April-July 2018. Data were weighted to match the English population on key sociodemographic characteristics.

RESULTS

Of e-cigarette users, 4.6% (95%CI 2.6-6.6) reported vaping for weight control, and 1.9% (95%CI 0.6-3.2) reported vaping to replace meals/snacks. It was rare for individuals who had smoked in the past year to have heard (8.8%, 95%CI 7.3-10.3) or believe (6.4%, 95%CI 5.1-7.7) that vaping could help control weight. Women (OR = 0.62, 95%CI 0.42-0.93) and older people (OR = 0.30, 95%CI 0.13-0.72) were less likely to have heard the claim and women were less likely to believe it (OR = 0.44, 95%CI 0.27-0.72). However, 13.4% (95%CI 11.3-15.5) and 13.1% (95%CI 11.0-15.2) of current smokers who did not use e-cigarettes said they would be more likely to try e-cigarettes or quit smoking, respectively, if vaping could help control their weight.

CONCLUSION

One in 16 English people who have smoked in the last year believe that vaping would prevent weight gain after stopping. One in 22 people who vape are using e-cigarettes for this purpose. However, should evidence emerge that e-cigarettes prevent weight gain, one in eight people who smoke would be tempted to quit smoking and use e-cigarettes.

Smoking and Increased White and Red Blood Cells

Objective—

Whether tobacco smoking causally affects white and red blood cells and thrombocyte counts is unknown. Using a Mendelian randomization approach, we tested the hypothesis that smoking causes increases in these blood cell indices.

Approach and Results—

We included 104 607 white Danes aged 20 to 100 years from the Copenhagen General Population Study with information on blood cell indices, smoking habits, and CHRNA3 (alpha 3 nicotinic cholinergic receptor) rs1051730 genotype, where the T allele causes higher tobacco consumption; 41 759 were former smokers and 17 852 current smokers. In multivariable adjusted observational analyses and compared with never smokers, white blood cells were associated with up to 19% increases, thrombocytes with up to 4.7% increases, and red blood cell indices with up to 2.3% increases in former and current smokers. All associations were dose dependent, with tobacco consumption but for white blood cells and thrombocytes also dependent on smoking cessation time in former smokers; highest increases were for <1-year smoking cessation and lowest increases for >10-year smoking cessation. In age- and sex-adjusted genetic analyses, percent differences per T allele increase in current smokers were 1.15% (95% CI, 0.61%–1.68%) for leukocytes, 1.07% (0.38%–1.76%) for neutrophils, 1.34% (0.66%–2.02%) for lymphocytes, 1.50% (0.83%–2.18%) for monocytes, −0.60% (−1.91% to 0.74%) for eosinophils, 0.17% (−0.94% to 1.29%) for basophils, 0.38% (−0.17% to 0.93%) for thrombocytes, 0.04% (−0.14% to 0.23%) for erythrocytes, 0.34% (0.17% to 0.50%) for hematocrit, 0.26% (0.09% to 0.43%) for hemoglobin, and 0.29% (0.18% to 0.41%) for mean corpuscular volume.

Conclusions—

Smoking causes increased blood leukocytes, neutrophils, lymphocytes, and monocytes, as well as increased hematocrit, hemoglobin, and mean corpuscular volume. The observational smoking relationships were long term for white blood cells and short term for red blood cell indices.

Body mass index and all cause mortality in HUNT and UK Biobank studies: linear and non-linear mendelian randomisation analyses

EDITOR'S NOTE

Please see the Editor's Note (doi: https://doi.org/10.1136/bmj.l1042) on Methodological Criticism and an Updated Analysis

OBJECTIVE

To investigate the shape of the causal relation between body mass index (BMI) and mortality.

DESIGN

Linear and non-linear mendelian randomisation analyses.

SETTING

Nord-Trøndelag Health (HUNT) Study (Norway) and UK Biobank (United Kingdom).

PARTICIPANTS

Middle to early late aged participants of European descent: 56 150 from the HUNT Study and 366 385 from UK Biobank.

MAIN OUTCOME MEASURES

All cause and cause specific (cardiovascular, cancer, and non-cardiovascular non-cancer) mortality.

RESULTS

12 015 and 10 344 participants died during a median of 18.5 and 7.0 years of follow-up in the HUNT Study and UK Biobank, respectively. Linear mendelian randomisation analyses indicated an overall positive association between genetically predicted BMI and the risk of all cause mortality. An increase of 1 unit in genetically predicted BMI led to a 5% (95% confidence interval 1% to 8%) higher risk of mortality in overweight participants (BMI 25.0-29.9) and a 9% (4% to 14%) higher risk of mortality in obese participants (BMI ≥30.0) but a 34% (16% to 48%) lower risk in underweight (BMI <18.5) and a 14% (-1% to 27%) lower risk in low normal weight participants (BMI 18.5-19.9). Non-linear mendelian randomisation indicated a J shaped relation between genetically predicted BMI and the risk of all cause mortality, with the lowest risk at a BMI of around 22-25 for the overall sample. Subgroup analyses by smoking status, however, suggested an always-increasing relation of BMI with mortality in never smokers and a J shaped relation in ever smokers.

CONCLUSIONS

The previously observed J shaped relation between BMI and risk of all cause mortality appears to have a causal basis, but subgroup analyses by smoking status revealed that the BMI-mortality relation is likely comprised of at least two distinct curves, rather than one J shaped relation. An increased risk of mortality for being underweight was only evident in ever smokers.

The associations between smoking and obesity in northeast China: a quantile regression analysis

Obesity is a risk factors of chronic diseases, and smoking is associated with both chronic diseases and obesity. There were some controversies about the associations between smoking and obesity. Thus, our study aimed to explore the associations of smoking with obesity, using body mass index (BMI) and waist circumference (WC) as obesity indices in northeast China. We enrolled a sample of 16,412 participants in Jilin province aged 18-79 in this study, which were derived from a cross-sectional survey in 2012. We used quantile regression (QR) models to identify the associations of smoking with obesity in different quantiles of BMI (or WC) by genders. The differences of BMI and WC by genders were statistically significant (p < 0.05). In conclusion, compared with current non-smokers, current smokers had lower BMI but higher WC. As increasing of WC, the association of WC with smoking was getting stronger, especially in females.

Associations of Body Mass and Fat Indexes With Cardiometabolic Traits

BACKGROUND

Body mass index (BMI) is criticized for not distinguishing fat from lean mass and ignoring fat distribution, leaving its ability to detect health effects unclear.

OBJECTIVES

The aim of this study was to compare BMI with total and regional fat indexes from dual-energy x-ray absorptiometry in their associations with cardiometabolic traits. Duration of exposure to and change in each index across adolescence were examined in relation to detailed traits in young adulthood.

METHODS

BMI was examined alongside total, trunk, arm, and leg fat indexes (each in kilograms per square meter) from dual-energy x-ray absorptiometry at ages 10 and 18 years in relation to 230 traits from targeted metabolomics at age 18 years in 2,840 offspring from the Avon Longitudinal Study of Parents and Children.

RESULTS

Higher total fat mass index and BMI at age 10 years were similarly associated with cardiometabolic traits at age 18 years, including higher systolic and diastolic blood pressure, higher very low-density lipoprotein and low-density lipoprotein cholesterol, lower high-density lipoprotein cholesterol, higher triglycerides, and higher insulin and glycoprotein acetyls. Associations were stronger for both indexes measured at age 18 years and for gains in each index from age 10 to 18 years (e.g., 0.45 SDs [95% confidence interval: 0.38 to 0.53] in glycoprotein acetyls per SD unit gain in fat mass index vs. 0.38 SDs [95% confidence interval: 0.27 to 0.48] per SD unit gain in BMI). Associations resembled those for trunk fat index. Higher lean mass index was weakly associated with traits and was not protective against higher fat mass index.

CONCLUSIONS

The results of this study support abdominal fatness as a primary driver of cardiometabolic dysfunction and BMI as a useful tool for detecting its effects.

A J-shaped relation of BMI and stroke: Systematic review and dose-response meta-analysis of 4.43 million participants

BACKGROUND AND AIM

Many studies have shown increased risk of stroke with greater adiposity as measured by body mass index (BMI), but questions remain about the shape of the dose-response relation. We conducted a systematic review and meta-analysis of prospective studies to clarify the strength and shape of the dose-response relation between BMI and risk of stroke.

METHODS AND RESULTS

PubMed and Embase databases were searched for articles published up to May 11, 2018. Random-effects generalized least-squares regression models were used to estimate study-specific dose-response association, and restricted cubic splines were used to model the association. We included reports of 44 prospective cohort studies describing 102 466 incident cases among 4 432 475 participants. With a 5-unit increment in BMI, the summary relative risk for stroke incidence was 1.10 (95% confidence interval, 1.06 to 1.13; I² = 88.0%). The dose-response relation was J-shaped (P_{non-linearity} <0.001). The risk was not increased at the low BMI range (<24 kg/m²), but was increased within the high BMI range (>25 kg/m²).

CONCLUSION

Both overweight and obesity increase the risk of stroke with a J-shaped dose-response relation, and the nadir of the curve was observed at BMI 23-24 kg/m².

Cigarette smoking and thyroid cancer risk: a cohort study

Background

We evaluated the association between smoking status and thyroid cancer risk and whether this association is mediated by body mass index (BMI) and thyroid-stimulating hormone (TSH).

Methods

We performed a cohort study of 96,855 Korean adults who were followed annually or biennially for a median of 5.9 years.

Results

During 511,052.9 person-years of follow-up, 1,250 participants developed thyroid cancer. In men, we observed a dose-dependent inverse association between current smoking, pack-years, and thyroid cancer. After adjustment for confounders, adjusted hazard ratios (95% confidence intervals) for thyroid cancer comparing current and former smokers to never smokers were 0.58 (0.45–0.75) and 0.93 (0.73–1.18), respectively. After further adjustment for BMI and TSH as potential mediators, this association was slightly attenuated, but remained significant. For women, current smokers tended to have a lower risk of thyroid cancer, but this association did not reach statistical significance.

Conclusions

In this cohort study, current smoking was associated with a decreased risk of incident thyroid cancer in men but not in women and this association was observed even after adjusting for TSH and BMI levels as potential mediators. Further mechanistic studies are needed to elucidate the possible effect of smoking on the pathogenesis of thyroid cancer development.

Body mass index, abdominal fatness, and the risk of sudden cardiac death: a systematic review and dose-response meta-analysis of prospective studies

Although overweight and obesity are established risk factors for some types of heart disease including ischemic heart disease, heart failure and atrial fibrillation, less is known about the association between adiposity and sudden cardiac death. We conducted a systematic review and meta-analysis of prospective studies to clarify the association between adiposity and risk of sudden cardiac death. PubMed and Embase databases were searched up to July 20th 2017. Summary relative risks (RRs) and 95% confidence intervals (CIs) were calculated using random effects models. The summary RR was 1.16 (95% CI 1.05-1.28, I2 = 68%, n = 14) per 5 unit increment in BMI, and 1.82 (95% CI 1.61-2.07, I2 = 0%, n = 3) per 0.1 unit increase in waist-to-hip ratio, and 1.03 (95% CI 0.93-1.15, I2 = 0%, n = 2) per 10 cm increase in waist circumference. The heterogeneity in the analysis of BMI and sudden cardiac death persisted across most subgroup analyses. The association was stronger among studies with longer follow-up compared to short follow-up and was observed in the European and American studies, but not in the Asian studies. There was a J-shaped association between BMI and sudden cardiac death and the lowest risk was observed in the normal weight range, however, the increased risk with a low BMI was attenuated among studies with a longer duration of follow-up. This meta-analysis suggest an increased risk of sudden cardiac death with increasing BMI and waist-to-hip ratio, however, further studies with stratification for smoking status are needed of waist circumference, weight changes and adiposity at younger ages.

Role of obesity in smoking behaviour: Mendelian randomisation study in UK Biobank

OBJECTIVE

To determine whether body mass index, body fat percentage, and waist circumference influence smoking status and intensity.

DESIGN

Mendelian randomisation study.

SETTING

UK Biobank, with replication of results from the Tobacco and Genetics (TAG) consortium.

PARTICIPANTS

European descent participants from the UK Biobank cohort (n=372 791) and the TAG consortium (n=74 035).

MAIN OUTCOME MEASURES

Risk of current and past smoking, number of cigarettes smoked per day, age of smoking initiation.

RESULTS

The Mendelian randomisation analysis indicated that each standard deviation increment in body mass index (4.6) increased the risk of being a smoker (odds ratio 1.18 (95% confidence interval 1.13 to 1.23), P<0.001). This association was replicated in the TAG consortium data (1.19 (1.06 to 1.33), P=0.003). Furthermore, each standard deviation increment in body mass index was estimated to increase smoking intensity by 0.88 cigarettes per day (95% confidence interval 0.50 to 1.26, P<0.001) in UK Biobank and 1.27 cigarettes per day in the TAG consortium (0.46 to 2.07, P=0.002). Similar results were also seen for body fat percentage and waist circumference in both UK Biobank and the TAG consortium data.

CONCLUSIONS

These results strongly suggest that higher adiposity influences smoking behaviour and could have implications for the implementation of public health interventions aiming to reduce the prevalence of these important risk factors.

Cigarette smoking and metabolic syndrome components: a cross-sectional study from Maracaibo City, Venezuela

Background: A growing body of evidence suggests that cigarette smoking can cause the onset of metabolic syndrome prior to cardiovascular diseases. Therefore, the objective of this study was to evaluate the relationship between smoking habit and metabolic syndrome components in an adult population from Maracaibo city, Venezuela. Methods: The Maracaibo City Metabolic Syndrome Prevalence Study is a descriptive, cross-sectional study with random and multi-stage sampling. In this sub-study, 2212 adults from both genders were selected. On the basis of their medical background, they were classified as smokers, non-smokers and former smokers. Metabolic syndrome was defined according to Harmonizing 2009 criteria, using population-specific abdominal circumference cut-off points. The association between risk factors was evaluated using a logistic regression model. Results: In the studied population, 14.8% were smokers, 15.4% were former smokers. In the multivariate analysis, the presence of metabolic syndrome (smokers: OR, 1.54; 95% CI, 1.11-2.14; p=0.010) and its components were related to cigarette smoking, with the exception of hyperglycemia. High blood pressure was inversely associated with current smoking status (smokers: OR, 0.70 (0.51-0.95); p=0.025). Conclusion: Cigarette smoking represents a related factor with metabolic syndrome, being associated with low high-density lipoprotein-cholesterol, increased abdominal circumference and elevated triacylglyceride levels. Former smokers did not present a greater risk for developing this metabolic disease when compared to non-smokers. The effect of avoiding this habit should be evaluated in future studies in our population.

Cigarette smoking and metabolic syndrome components: a cross-sectional study from Maracaibo City, Venezuela

Background: A growing body of evidence suggests that cigarette smoking can cause the onset of metabolic syndrome prior to cardiovascular diseases. Therefore, the objective of this study was to evaluate the relationship between smoking habit and metabolic syndrome components in an adult population from Maracaibo city, Venezuela. Methods: The Maracaibo City Metabolic Syndrome Prevalence Study is a descriptive, cross-sectional study with random and multi-stage sampling. In this sub-study, 2212 adults from both genders were selected. On the basis of their medical background, they were classified as smokers, non-smokers and former smokers. Metabolic syndrome was defined according to Harmonizing 2009 criteria, using population-specific abdominal circumference cut-off points. The association between risk factors was evaluated using a logistic regression model. Results: In the studied population, 14.8% were smokers, 15.4% were former smokers. In the multivariate analysis, the presence of metabolic syndrome (smokers: OR, 1.54; 95% CI, 1.11-2.14; p=0.010) and its components were related to cigarette smoking, with the exception of hyperglycemia. High blood pressure was inversely associated with current smoking status (smokers: OR, 0.70 (0.51-0.95); p=0.025). Conclusion: Cigarette smoking represents a related factor with metabolic syndrome, being associated with low high-density lipoprotein-cholesterol, increased abdominal circumference and elevated triacylglyceride levels. Former smokers did not present a greater risk for developing this metabolic disease when compared to non-smokers. The effect of avoiding this habit should be evaluated in future studies in our population.

Cigarette smoking and metabolic syndrome components: a cross-sectional study from Maracaibo City, Venezuela

Background: A growing body of evidence suggests that cigarette smoking can cause the onset of metabolic syndrome prior to cardiovascular diseases. Therefore, the objective of this study was to evaluate the relationship between smoking habit and metabolic syndrome components in an adult population from Maracaibo city, Venezuela. Methods: The Maracaibo City Metabolic Syndrome Prevalence Study is a descriptive, cross-sectional study with random and multi-stage sampling. In this sub-study, 2212 adults from both genders were selected. On the basis of their medical background, they were classified as smokers, non-smokers and former smokers. Metabolic syndrome was defined according to Harmonizing 2009 criteria, using population-specific abdominal circumference cut-off points. The association between risk factors was evaluated using a logistic regression model. Results: In the studied population, 14.8% were smokers, 15.4% were former smokers. In the multivariate analysis, the presence of metabolic syndrome (smokers: OR, 1.54; 95% CI, 1.11-2.14; p=0.010) and its components were related to cigarette smoking, with the exception of hyperglycemia. High blood pressure was inversely associated with current smoking status (smokers: OR, 0.70 (0.51-0.95); p=0.025). Conclusion: Cigarette smoking represents an independent risk factor for the development of metabolic syndrome, being associated with low high-density lipoprotein-cholesterol, increased abdominal circumference and elevated triacylglyceride levels. Former smokers did not present a greater risk for developing this metabolic disease when compared to non-smokers. The effect of avoiding this habit should be evaluated in future studies in our population.

Coffee intake, cardiovascular disease and all-cause mortality: observational and Mendelian randomization analyses in 95 000-223 000 individuals

Background

Coffee has been associated with modestly lower risk of cardiovascular disease and all-cause mortality in meta-analyses; however, it is unclear whether these are causal associations. We tested first whether coffee intake is associated with cardiovascular disease and all-cause mortality observationally; second, whether genetic variations previously associated with caffeine intake are associated with coffee intake; and third, whether the genetic variations are associated with cardiovascular disease and all-cause mortality.

Methods

First, we used multivariable adjusted Cox proportional hazard regression models evaluated with restricted cubic splines to examine observational associations in 95 366 White Danes. Second, we estimated mean coffee intake according to five genetic variations near the AHR (rs4410790; rs6968865) and CYP1A1/2 genes (rs2470893; rs2472297; rs2472299). Third, we used sex- and age adjusted Cox proportional hazard regression models to examine genetic associations with cardiovascular disease and all-cause mortality in 112 509 Danes. Finally, we used sex and age-adjusted logistic regression models to examine genetic associations with ischaemic heart disease including the Cardiogram and C4D consortia in a total of up to 223 414 individuals. We applied similar analyses to ApoE genotypes associated with plasma cholesterol levels, as a positive control.

Results

In observational analyses, we observed U-shaped associations between coffee intake and cardiovascular disease and all-cause mortality; lowest risks were observed in individuals with medium coffee intake. Caffeine intake allele score (rs4410790 + rs2470893) was associated with a 42% higher coffee intake. Hazard ratios per caffeine intake allele were 1.02 (95% confidence interval: 1.00-1.03) for ischaemic heart disease, 1.02 (0.99-1.02) for ischaemic stroke, 1.02 (1.00-1.03) for ischaemic vascular disease, 1.02 (0.99-1.06) for cardiovascular mortality and 1.01 (0.99-1.03) for all-cause mortality. Including international consortia, odds ratios per caffeine intake allele for ischaemic heart disease were 1.00 (0.98-1.02) for rs4410790, 1.01 (0.99-1.03) for rs6968865, 1.02 (1.00-1.04) for rs2470893, 1.02 (1.00-1.04) for rs2472297 and 1.03 (0.99-1.06) for rs2472299. Conversely, 5% lower cholesterol level caused by ApoE genotype had a corresponding odds ratio for ischaemic heart disease of 0.93 (0.89-0.97).

Conclusions

Observationally, coffee intake was associated with U-shaped lower risk of cardiovascular disease and all-cause mortality; however, genetically caffeine intake was not associated with risk of cardiovascular disease or all-cause mortality.

Genetic polymorphisms associated with smoking behaviour predict the risk of surgery in patients with Crohn's disease

BACKGROUND

Smoking is a strong environmental factor leading to adverse outcomes in Crohn's disease, but a more benign course in ulcerative colitis. Several single nucleotide polymorphisms (SNPs) are associated with smoking quantity and behaviour.

AIM

To assess whether smoking-associated SNPs interact with smoking to influence the clinical course of inflammatory bowel diseases.

METHODS

Genetic and prospectively obtained clinical data from 1434 Swiss inflammatory bowel disease cohort patients (821 Crohn's disease and 613 ulcerative colitis) were analysed. Six SNPs associated with smoking quantity and behaviour (rs588765, rs1051730, rs1329650, rs4105144, rs6474412 and rs3733829) were combined to form a risk score (range: 0-12) by adding the number of risk alleles. We calculated multivariate models for smoking, risk of surgery, fistula, Crohn's disease location and ulcerative colitis disease extent.

RESULTS

In Crohn's disease patients who smoke, the number of surgeries was associated with the genetic risk score. This translates to a predicted 3.5-fold (95% confidence interval: 2.4- to 5.7-fold, P<.0001) higher number of surgical procedures in smokers with 12 risk alleles than individuals with the lowest risk. Patients with a risk score >7 had a significantly shorter time to first intestinal surgery. The genetic risk score did not predict surgery in ulcerative colitis or occurrence of fistulae in Crohn's disease. SNP rs6265 was associated with ileal disease in Crohn's disease (P<.05) and proctitis in ulcerative colitis (P<.05).

CONCLUSIONS

SNPs associated with smoking quantity is associated with an increased risk for surgery in Crohn's disease patients who smoke. Our data provide an example of genetics interacting with the environment to influence the disease course of inflammatory bowel disease.

Continuous outcome logistic regression for analyzing body mass index distributions

Body mass indices (BMIs) are applied to monitor weight status and associated health risks in populations.  Binary or multinomial logistic regression models are commonly applied in this context, but are only applicable to BMI values categorized within a small set of defined ad hoc BMI categories.  This approach precludes comparisons with studies and models based on different categories.  In addition, ad hoc categorization of BMI values prevents the estimation and analysis of the underlying continuous BMI distribution and leads to information loss.  As an alternative to multinomial regression following ad hoc categorization, we propose a continuous outcome logistic regression model for the estimation of a continuous BMI distribution.  Parameters of interest, such as odds ratios for specific categories, can be extracted from this model post hoc in a general way.  A continuous BMI logistic regression that describes BMI distributions avoids the necessity of ad hoc and post hoc category choice and simplifies between-study comparisons and pooling of studies for joint analyses.  The method was evaluated empirically using data from the Swiss Health Survey.

Obesity, metabolic factors and risk of different histological types of lung cancer: A Mendelian randomization study

BACKGROUND

Assessing the relationship between lung cancer and metabolic conditions is challenging because of the confounding effect of tobacco. Mendelian randomization (MR), or the use of genetic instrumental variables to assess causality, may help to identify the metabolic drivers of lung cancer.

METHODS AND FINDINGS

We identified genetic instruments for potential metabolic risk factors and evaluated these in relation to risk using 29,266 lung cancer cases (including 11,273 adenocarcinomas, 7,426 squamous cell and 2,664 small cell cases) and 56,450 controls. The MR risk analysis suggested a causal effect of body mass index (BMI) on lung cancer risk for two of the three major histological subtypes, with evidence of a risk increase for squamous cell carcinoma (odds ratio (OR) [95% confidence interval (CI)] = 1.20 [1.01-1.43] and for small cell lung cancer (OR [95%CI] = 1.52 [1.15-2.00]) for each standard deviation (SD) increase in BMI [4.6 kg/m2]), but not for adenocarcinoma (OR [95%CI] = 0.93 [0.79-1.08]) (Pheterogeneity = 4.3x10-3). Additional analysis using a genetic instrument for BMI showed that each SD increase in BMI increased cigarette consumption by 1.27 cigarettes per day (P = 2.1x10-3), providing novel evidence that a genetic susceptibility to obesity influences smoking patterns. There was also evidence that low-density lipoprotein cholesterol was inversely associated with lung cancer overall risk (OR [95%CI] = 0.90 [0.84-0.97] per SD of 38 mg/dl), while fasting insulin was positively associated (OR [95%CI] = 1.63 [1.25-2.13] per SD of 44.4 pmol/l). Sensitivity analyses including a weighted-median approach and MR-Egger test did not detect other pleiotropic effects biasing the main results.

CONCLUSIONS

Our results are consistent with a causal role of fasting insulin and low-density lipoprotein cholesterol in lung cancer etiology, as well as for BMI in squamous cell and small cell carcinoma. The latter relation may be mediated by a previously unrecognized effect of obesity on smoking behavior.

Unemployment, underweight, and obesity: Findings from Understanding Society (UKHLS)

Elevated morbidity and mortality among jobseekers may be partly explained by adiposity, but previous studies of unemployment and body mass index (BMI), which have usually modelled associations as linear, have produced inconsistent results. However, both underweight and obesity are associated with mortality, and both weight loss and weight gain associated with a stressful environment. If unemployment is associated with both underweight and obesity for different subgroups, these associations may previously have masked each other, whilst affecting health through divergent pathways. We investigated whether there is a previously overlooked U-shaped association of unemployment and BMI, which could help explain jobseekers' elevated morbidity and mortality, and identify groups vulnerable to underweight and obesity during unemployment. We used multinomial models to simultaneously investigate associations of unemployment with BMI-defined underweight, overweight, and obesity in 10,737 working-age UK adults from Understanding Society (UKHLS) in 2010-12. Moderating impacts of unemployment duration, demographic factors and smoking were explored. Current jobseekers were more likely to be underweight (Odds ratio (OR): 4.05, 95% confidence interval (CI): 2.12-7.73) and less likely to be overweight (OR: 0.71, CI: 0.55, 0.92) adjusted for gender, age, education, health, smoking and physical activity, while unemployed non-smokers had increased odds of obesity (OR: 1.52, CI: 1.06-2.18). Underweight and overweight associations were more apparent for longer-term jobseekers, men, and jobseekers from lower-income households. We conclude that unemployment is associated with underweight and, in nonsmokers, obesity. Results show the unemployment-adiposity relationship cannot be properly studied assuming unidirectionality of effects, and suggest unemployment may affect health of different groups via divergent adiposity-mediated pathways.

Body mass index as a predictor of healthy and disease-free life expectancy between ages 50 and 75: a multicohort study

BACKGROUND

While many studies have shown associations between obesity and increased risk of morbidity and mortality, little comparable information is available on how body mass index (BMI) impacts health expectancy. We examined associations of BMI with healthy and chronic disease-free life expectancy in four European cohort studies.

METHODS

Data were drawn from repeated waves of cohort studies in England, Finland, France and Sweden. BMI was categorized into four groups from normal weight (18.5-24.9 kg m^-2) to obesity class II (⩾35 kg m^-2). Health expectancy was estimated with two health indicators: sub-optimal self-rated health and having a chronic disease (cardiovascular disease, cancer, respiratory disease and diabetes). Multistate life table models were used to estimate sex-specific healthy life expectancy and chronic disease-free life expectancy from ages 50 to 75 years for each BMI category.

RESULTS

The proportion of life spent in good perceived health between ages 50 and 75 progressively decreased with increasing BMI from 81% in normal weight men and women to 53% in men and women with class II obesity which corresponds to an average 7-year difference in absolute terms. The proportion of life between ages 50 and 75 years without chronic diseases decreased from 62 and 65% in normal weight men and women and to 29 and 36% in men and women with class II obesity, respectively. This corresponds to an average 9 more years without chronic diseases in normal weight men and 7 more years in normal weight women between ages 50 and 75 years compared to class II obese men and women. No consistent differences were observed between cohorts.

CONCLUSIONS

Excess BMI is associated with substantially shorter healthy and chronic disease-free life expectancy, suggesting that tackling obesity would increase years lived in good health in populations.

The CHRNA5-A3-B4 Gene Cluster and Smoking: From Discovery to Therapeutics

Genome-wide association studies (GWASs) have identified associations between the CHRNA5-CHRNA3-CHRNB4 gene cluster and smoking heaviness and nicotine dependence. Studies in rodents have described the anatomical localisation and function of the nicotinic acetylcholine receptors (nAChRs) formed by the subunits encoded by this gene cluster. Further investigations that complemented these studies highlighted the variability of individuals' smoking behaviours and their ability to adjust nicotine intake. GWASs of smoking-related health outcomes have also identified this signal in the CHRNA5-CHRNA3-CHRNB4 gene cluster. This insight underpins approaches to strengthen causal inference in observational data. Combining genetic and mechanistic studies of nicotine dependence and smoking heaviness may reveal novel targets for medication development. Validated targets can inform genetic therapeutic interventions for smoking cessation and tobacco-related diseases.

Smoking status and abdominal obesity among normal- and overweight/obese adults: Population-based FINRISK study

Several studies have reported direct associations of smoking with body mass index (BMI) and abdominal obesity. However, the interplay between them is poorly understood. Our first aim was to investigate the interaction between smoking status and BMI on abdominal obesity (waist circumference, WC). Our second aim was to examine how the association of smoking status with WC varies among normal and overweight/obese men and women. We examined 5833 participants from the National FINRISK 2007 Study. The interactions between smoking and BMI on WC were analyzed. Participants were categorized into eight groups according to BMI (normal weight vs. overweight/obese) and smoking status (never smoker, ex-smoker, occasional/light/moderate daily smoker, heavy daily smoker). The associations between each BMI/smoking status -group and WC were analyzed by multiple regressions, the normal-weight never smokers as the reference group. The smoking status by BMI-interaction on WC was significant for women, but not for men. Among the overweight/obese women, ex-smokers (β = 2.73; 1.99, 3.46) and heavy daily smokers (β = 4.90; 3.35, 6.44) had the highest estimates for WC when adjusted for age, BMI, alcohol consumption and physical activity. In comparison to never smoking overweight/obese women, the β-coefficients of ex-smokers and heavy daily smokers were significantly higher. Among men and normal weight women the β -coefficients did not significantly differ by smoking status. An interaction between smoking status and BMI on abdominal obesity was observed in women: overweight/obese heavy daily smokers were particularly vulnerable for abdominal obesity. This risk group should be targeted for cardiovascular disease prevention.

Changes in adiposity in an older Chinese population in rapid economic transition

OBJECTIVE

To examine the changes in body mass index (BMI) and waist circumference (WC) in Guangzhou, South China, which is probably experiencing the most rapid economic transition in history.

METHODS

In this study, 17,786 Chinese aged 50+ years were recruited from 2003 to 2008 and followed up until 2012. BMI and WC were measured at two time points.

RESULTS

During the mean follow-up of 3.6 years (median = 3, interquartile = 1), age-adjusted mean BMI increased only slightly. By contrast, mean WC increased sharply by 0.94 cm (95% confidence interval 0.93-0.94) annually in men and 1.29 cm (1.28-1.29) annually in women. In 77% of women and 69% of men, WC increased, and among them, the mean annual increase was 2.01 cm and 1.70 cm, respectively. Among healthy, never-smoking participants, the incidence of central obesity was 29.0% (36.4% in women and 14.2% in men). The incidence of general obesity was 1.9% and was similarly low in both men and women (2.1% vs. 1.8%). Conversely, 20.3% of individuals with general obesity became nonobese, and 12.8% of individuals with central obesity returned to normal.

CONCLUSIONS

Central obesity has risen sharply in this cohort. Such increases may have been greatly underestimated previously and should form the basis of an even stronger warning for regions undergoing economic transitions in China and elsewhere.