A modifiable risk factors atlas of lung cancer: A Mendelian randomization study

Total testosterone plays a crucial role in the pathway from hypothyroidism to broad depression in women

BACKGROUND

Depression tends to develop in correlation with hypothyroidism, however it's unclear how testosterone traits contribute to this association. We examined the causal association between depression, testosterone traits, and hypothyroidism using Mendelian randomization (MR).

METHOD

We conducted univariable and multivariable MR studies using summary-level statistics from genome-wide association studies (GWAS) of Hypothyroidism (n = 213,990), broad depression (n = 322,580), probable major depressive disorder (probable MDD) (n = 174,519), and International Classification of Diseases (ICD)-9 or ICD-10-coded MDD (n = 217,584) from European ancestry. The inverse variance weighted (IVW) method was used as the main MR analysis.

RESULTS

In univariate MR analysis, there is a positive causal relationship between hypothyroidism and broad depression (P = 0.0074; OR = 1.0066; 95%CI: 1.0018-1.0114) and probable MDD (P = 0.0242; OR = 1.0056; 95%CI: 1.0007-1.0105). In females, there is a causal relationship between hypothyroidism and decreased total testosterone (P < 0.001; OR = 0.9747; 95%CI: 0.9612-0.9885) and sex hormone binding globulin (SHBG) levels (P = 0.0418; OR = 0.9858; 95%CI: 0.9723-0.9995). In females, there is an inverse causal relationship between total testosterone and broad depression (P = 0.0349; OR = 0.9898; 95%CI: 0.9804-0.9993). Furthermore, in multivariate MR analysis, after adjusting for total testosterone in females, hypothyroidism only has a positive causal relationship with probable MDD, and the relationship with broad depression is no longer significant. Most notably, after adjusting for hypothyroidism, the inverse causal effect of female total testosterone levels on broad depression becomes more significant (P = 0.0154; OR = 0.9878; 95%CI: 0.9780-0.9977).

CONCLUSION

Hypothyroidism increases the risk of broad depression and probable MDD development. Total Testosterone appears to play an important role in the relationship between hypothyroidism and broad depression in female.

Socioeconomic traits and the risk of Barrett’s esophagus and gastroesophageal reflux disease: A Mendelian randomization study

BACKGROUND

Previous observational studies have shown that the prevalence of gastroesophageal reflux disease (GERD) and Barrett’s esophagus (BE) is associated with socioeconomic status. However, due to the methodological limitations of traditional observational studies, it is challenging to definitively establish causality.

AIM

To explore the causal relationship between the prevalence of these conditions and socioeconomic status using Mendelian randomization (MR).

METHODS

We initially screened single nucleotide polymorphisms (SNPs) to serve as proxies for eight socioeconomic status phenotypes for univariate MR analysis. The inverse variance weighted (IVW) method was used as the primary analytical method to estimate the causal relationship between the eight socioeconomic status phenotypes and the risk of GERD and BE. We then collected combinations of SNPs as composite proxies for the eight socioeconomic phenotypes to perform multivariate MR (MVMR) analyses based on the IVW MVMR model. Furthermore, a two-step MR mediation analysis was used to examine the potential mediation of the associations by body mass index, major depressive disorder (MDD), smoking, alcohol consumption, and sleep duration.

RESULTS

The study identified three socioeconomic statuses that had a significant impact on GERD. These included household income [odds ratio (OR): 0.46; 95% confidence interval (95%CI): 0.31-0.70], education attainment (OR: 0.23; 95%CI: 0.18-0.29), and the Townsend Deprivation Index at recruitment (OR: 1.57; 95%CI: 1.04-2.37). These factors were found to independently and predominantly influence the genetic causal effect of GERD. Furthermore, the mediating effect of educational attainment on GERD was found to be mediated by MDD (proportion mediated: 10.83%). Similarly, the effect of educational attainment on BE was mediated by MDD (proportion mediated: 10.58%) and the number of cigarettes smoked per day (proportion mediated: 3.50%). Additionally, the mediating effect of household income on GERD was observed to be mediated by sleep duration (proportion mediated: 9.75%)

CONCLUSION

This MR study shed light on the link between socioeconomic status and GERD or BE, providing insights for the prevention of esophageal cancer and precancerous lesions.

Socioeconomic traits and the risk of Barrett's esophagus and gastroesophageal reflux disease: A Mendelian randomization study

BACKGROUND

Previous observational studies have shown that the prevalence of gastroesophageal reflux disease (GERD) and Barrett's esophagus (BE) is associated with socioeconomic status. However, due to the methodological limitations of traditional observational studies, it is challenging to definitively establish causality.

AIM

To explore the causal relationship between the prevalence of these conditions and socioeconomic status using Mendelian randomization (MR).

METHODS

We initially screened single nucleotide polymorphisms (SNPs) to serve as proxies for eight socioeconomic status phenotypes for univariate MR analysis. The inverse variance weighted (IVW) method was used as the primary analytical method to estimate the causal relationship between the eight socioeconomic status phenotypes and the risk of GERD and BE. We then collected combinations of SNPs as composite proxies for the eight socioeconomic phenotypes to perform multivariate MR (MVMR) analyses based on the IVW MVMR model. Furthermore, a two-step MR mediation analysis was used to examine the potential mediation of the associations by body mass index, major depressive disorder (MDD), smoking, alcohol consumption, and sleep duration.

RESULTS

The study identified three socioeconomic statuses that had a significant impact on GERD. These included household income [odds ratio (OR): 0.46; 95% confidence interval (95%CI): 0.31-0.70], education attainment (OR: 0.23; 95%CI: 0.18-0.29), and the Townsend Deprivation Index at recruitment (OR: 1.57; 95%CI: 1.04-2.37). These factors were found to independently and predominantly influence the genetic causal effect of GERD. Furthermore, the mediating effect of educational attainment on GERD was found to be mediated by MDD (proportion mediated: 10.83%). Similarly, the effect of educational attainment on BE was mediated by MDD (proportion mediated: 10.58%) and the number of cigarettes smoked per day (proportion mediated: 3.50%). Additionally, the mediating effect of household income on GERD was observed to be mediated by sleep duration (proportion mediated: 9.75%).

CONCLUSION

This MR study shed light on the link between socioeconomic status and GERD or BE, providing insights for the prevention of esophageal cancer and precancerous lesions.

Different effects of 24 dietary intakes on gastroesophageal reflux disease: A mendelian randomization

BACKGROUND

In observational studies, dietary intakes are associated with gastroesophageal reflux disease (GERD).

AIM

To conduct a two-sample mendelian randomization (MR) analysis to determine whether those associations are causal.

METHODS

To explore the relationship between dietary intake and the risk of GERD, we extracted appropriate single nucleotide polymorphisms from genome-wide association study data on 24 dietary intakes. Three methods were adopted for data analysis: Inverse variance weighting, weighted median methods, and MR-Egger's method. The odds ratio (OR) and 95% confidence interval (CI) were used to evaluate the causal association between dietary intake and GERD.

RESULTS

Our univariate Mendelian randomization (UVMR) results showed significant evidence that pork intake (OR, 2.83; 95%CI: 1.76-4.55; P = 1.84 × 10-5), beer intake (OR, 2.70, 95%CI: 2.00-3.64; P = 6.54 × 10-11), non-oily fish intake (OR, 2.41; 95%CI: 1.49-3.91; P = 3.59 × 10-4) have a protective effect on GERD. In addition, dried fruit intake (OR, 0.37; 95%CI: 0.27-0.50; 6.27 × 10-11), red wine intake (OR, 0.34; 95%CI: 0.25-0.47; P = 1.90 × 10-11), cheese intake (OR, 0.46; 95%CI: 0.39-0.55; P =3.73 × 10-19), bread intake (OR, 0.72; 95%CI: 0.56-0.92; P = 0.0009) and cereal intake (OR, 0.45; 95%CI: 0.36-0.57; P = 2.07 × 10-11) were negatively associated with the risk of GERD. There was a suggestive association for genetically predicted coffee intake (OR per one SD increase, 1.22, 95%CI: 1.03-1.44; P = 0.019). Multivariate Mendelian randomization further confirmed that dried fruit intake, red wine intake, cheese intake, and cereal intake directly affected GERD. In contrast, the impact of pork intake, beer intake, non-oily fish intake, and bread intake on GERD was partly driven by the common risk factors for GERD. However, after adjusting for all four elements, there was no longer a suggestive association between coffee intake and GERD.

CONCLUSION

This study provides MR evidence to support the causal relationship between a broad range of dietary intake and GERD, providing new insights for the treatment and prevention of GERD.

Biochemical changes in lipid and protein metabolism caused by mannose-Raman spectroscopy studies

Biochemical analysis of human normal bronchial cells (BEpiC) and human cancer lung cells (A549) has been performed by using Raman spectroscopy and Raman imaging. Our approach provides a biochemical compositional mapping of the main cell components: nucleus, mitochondria, lipid droplets, endoplasmic reticulum, cytoplasm and cell membrane. We proved that Raman spectroscopy and Raman imaging can distinguish successfully BEpiC and A549 cells. In this study, we have focused on the role of mannose in cancer development. It has been shown that changes in the concentration of mannose can regulate some metabolic processes in cells. Presented results suggest lipids and proteins can be considered as Raman biomarkers during lung cancer progression. Analysis obtained for bands 1444 cm-1, and 2854 cm-1 characteristic for lipids and derivatives proved that the addition of mannose reduced levels of these compounds. Results obtained for protein compounds based on bands 858 cm-1, 1004 cm-1 and 1584 cm-1 proved that the addition of mannose increases the values of protein in BEpiC cells and blocks protein glycolisation in A549 cells. Noticing Raman spectral changes in BEpiC and A549 cells supplemented with mannose can help to understand the mechanism of sugar metabolism during cancer development and could play in the future an important role in clinical treatment.

Impact of particulate-matter air pollution on 25-hydroxyvitamin D levels: a mendelian randomisation study

OBJECTIVES

In observational studies, the 25-hydroxyvitamin D (25(OH)D) level in body has been found to be closely related to particulate matter (PM) air pollution. In this study, we used the two-sample mendelian randomisation (MR) method to investigate and discuss the potential causal relationship and mode of influence.

STUDY DESIGN

MR study.

METHODS

PM data (PM10, PM2.5-10, PM2.5, PM2.5 absorbance) came from the UK Biobank database, and 25(OH)D data came from European Bioinformatics Institute (EBI) database. The analysis was conducted utilising three prominent methods (inverse-variance-weighted [IVW], MR-Egger, weighted median, weighted mode, and simple mode). The primary emphasis was placed on IVW, accompanied by heterogeneity and horizontal pleiotropy tests. Furthermore, sensitivity analysis was undertaken.

RESULTS

The MR analysis revealed a significant association between exposure to PM10 and a decrease in levels of 25(OH)D (odds ratio [OR]: 0.878, 95% confidence interval [CI]: 0.789-0.977). However, no significant relationship was observed between PM2.5 exposure and 25(OH)D (OR: 0.943, 95%CI: 0.858-1.037). Further analysis indicated that the main contributor to the decline in 25(OH)D levels is linked to PM2.5-10 exposure (OR: 0.840, 95%CI: 0.751-0.940) and PM2.5 absorbance (OR: 0.875, 95%CI: 0.824-0.929). No heterogeneity and horizontal pleiotropy existed.

CONCLUSIONS

The MR results suggest that PM (PM10, PM2.5-10 and PM2.5 absorbance) exposure lowers vitamin D (VD) levels, but PM2.5 was not found to have a significant effect on VD in humans.

Iron status and sarcopenia-related traits: a bi-directional Mendelian randomization study

Although serum iron status and sarcopenia are closely linked, the presence of comprehensive evidence to establish a causal relationship between them remains insufficient. The objective of this study is to employ Mendelian randomization techniques to clarify the association between serum iron status and sarcopenia. We conducted a bi-directional Mendelian randomization (MR) analysis to investigate the potential causal relationship between iron status and sarcopenia. MR analyses were performed using inverse variance weighted (IVW), MR-Egger, and weighted median methods. Additionally, sensitivity analyses were conducted to verify the reliability of the causal association results. Then, we harvested a combination of SNPs as an integrated proxy for iron status to perform a MVMR analysis based on IVW MVMR model. UVMR analyses based on IVW method identified causal effect of ferritin on appendicular lean mass (ALM, β = - 0.051, 95% CI - 0.072, - 0.031, p = 7.325 × 10-07). Sensitivity analyses did not detect pleiotropic effects or result fluctuation by outlying SNPs in the effect estimates of four iron status on sarcopenia-related traits. After adjusting for PA, the analysis still revealed that each standard deviation higher genetically predicted ferritin was associated with lower ALM (β = - 0.054, 95% CI - 0.092, - 0.015, p = 0.006). Further, MVMR analyses determined a predominant role of ferritin (β = - 0.068, 95% CI - 0.12, - 0.017, p = 9.658 × 10-03) in the associations of iron status with ALM. Our study revealed a causal association between serum iron status and sarcopenia, with ferritin playing a key role in this relationship. These findings contribute to our understanding of the complex interplay between iron metabolism and muscle health.

Associations between breakfast skipping and outcomes in neuropsychiatric disorders, cognitive performance, and frailty: a Mendelian randomization study

BACKGROUND

Prior studies have identified a correlation between breakfast skipping and a heightened risk of mental health issues. This investigation aimed to employ a Two-Sample Mendelian Randomization (MR) approach to explore the potential causal links between breakfast skipping and various psychiatric, neurological disorders, cognitive performance, and frailty.

METHODS

Utilizing data from genome-wide association studies within European demographics, this research scrutinized the association between breakfast habits and several neuropsychiatric conditions and physical health outcomes, including Alzheimer's disease (AD), Attention Deficit Hyperactivity Disorder (ADHD), Bipolar Disorder (BD), Major Depressive Disorder (MDD), Narcolepsy, Insomnia, cognitive performance, and frailty. In this MR analysis, the Inverse Variance Weighted (IVW) method was primarily utilized for evaluation. Outcomes were reported as Odds Ratios (OR) and regression coefficients (β), and underwent validation through False Discovery Rate (FDR) corrections, thereby offering a rigorous evaluation of the effects of breakfast habits on both mental and physical health dimensions.

RESULTS

Findings demonstrate a significant causal link between skipping breakfast and an increased risk of ADHD (OR = 2.74, 95%CI: 1.54-4.88, PFDR = 0.003) and MDD (OR = 1.7, 95%CI: 1.22-2.37, PFDR = 0.005). Conversely, no substantial causal associations were identified between breakfast skipping and AD, BD, narcolepsy, or insomnia (PFDR > 0.05). Moreover, a notable causal relationship was established between skipping breakfast and a reduction in cognitive performance (β = -0.16, 95%CI: -0.29-0.04, PFDR = 0.024) and an increase in frailty (β = 0.29, 95%CI: 0.12-0.45, PFDR = 0.003).

CONCLUSION

The MR analysis reveals that skipping breakfast is associated with an increased risk of ADHD, MDD, decreased cognitive performance, and greater frailty, while showing no associations were found with AD, BD, narcolepsy, or insomnia. These findings warrant further investigation into the underlying mechanisms and emphasize the importance of regular breakfast consumption for mental and physical well-being.

Heritable Traits and Lung Cancer Risk: A Two-Sample Mendelian Randomization Study

INTRODUCTION

Lung cancer is a complex polygenic disorder. Analysis with Mendelian randomization (MR) allows for genetically predicted risks to be estimated between exposures and outcomes.

METHODS

We analyzed 345 heritable traits from the United Kingdom Biobank and estimated their associated effects on lung cancer outcomes using two sample MR. In addition to estimating effects with overall lung cancer, adenocarcinoma, small cell lung cancer, and squamous cell lung cancers, we performed conditional effect modeling with multivariate MR (MVMR) and the traits of alcohol use, smoking initiation, average pre-tax income, and educational attainment.

RESULTS

Univariate MR provided evidence for increased age at first sexual intercourse (OR, 0.55; P = 6.15 × 10-13), educational attainment (OR, 0.24; P = 1.07 × 10-19), average household income (OR, 0.58; P = 7.85 × 10-05), and alcohol usually taken with meals (OR, 0.19; P = 1.06 × 10-06) associating with decreased odds of overall lung cancer development. In contrast, a lack of additional educational attainment (OR, 8.00; P = 3.48 × 10-12), body mass index (OR, 1.28; P = 9.00 × 10-08), pack years smoking as a proportion of life span (OR, 9.93; P = 7.96 × 10-12), and weekly beer intake (OR, 3.48; P = 4.08 × 10-07) were associated with an increased risk of overall lung cancer development.

CONCLUSIONS

Many heritable traits associated with an increased or inverse risk of lung cancer development. Effects vary based on histologic subtype and conditional third trait exposures.

IMPACT

We identified several heritable traits and presented their genetically predictable impact on lung cancer development, providing valuable insights for consideration.

Detecting potential causal relationship between inflammatory bowel disease and rosacea using bi-directional Mendelian randomization

The association between rosacea and inflammatory bowel disease (IBD) has been studied in previous observational studies. It is unclear, however, whether the association is causal or not. Independent genetic variants for IBD were chosen as instruments from published Genome-wide association studies (GWAS) studies involving 38,155 cases with an IBD diagnosis and 48,485 controls in order to investigate the causal effect of IBD on rosacea. Summarized data for rosacea were gathered from various GWAS studies that included 1195 cases and 211,139 controls without rosacea. Reverse-direction Mendelian randomization (MR) analysis was done to investigate the relationship between genetically proxied rosacea and IBD. With the use of the inverse variance-weighted (IVW), MR-Egger, and weighted median approaches, a 2-sample Mendelian randomization study was carried out. Analysis of heterogeneity and sensitivity was performed to examine the pleiotropy and robustness of effect estimates. The forward-direction of the MR study was to reveal that genetic predisposition to IBD including its two main subtypes: Crohn's disease (CD) and ulcerative colitis (UC) was associated with an increased risk of rosacea. The reverse-direction MR analyses did not demonstrate that a genetic predisposition to rosacea was associated with total IBD, UC and CD. Our findings provided evidence for a causal impact of IBD, UC, and CD on rosacea, but not vice versa. The elevated incidence of rosacea in patients with IBD should be recognized by doctors to make an early diagnosis and initiate specialized therapy.

Lifestyle factors and the risk of gallstones: results from the national health and nutrition examination survey 2018-2020 and mendelian randomization analysis

OBJECTIVES

This study aimed to investigate the relationship between lifestyle and gallstones.

MATERIALS AND METHODS

We performed an observational study using the 2018-2020 National Health and Nutrition Examination Survey (NHANES). Univariate and multivariate-adjusted logistic regression analyses were performed to assess the correlations between lifestyle factors and gallstone risk. Second, Mendelian randomization (MR) was applied to decrease the causal relationship between lifestyle factors and gallstones.

RESULTS

This observational study enrolled 11,970 individuals. The risk of gallstones was found to increase with increased sitting time (odds ratio (OR) 1.03, 95% CI 1.00-1.05, p = 0.02). In contrast, the risk of gallstones was found to decrease with recreational activity (OR 0.50, 95% CI 0.29-0.87, p = 0.02). The results of the MR also showed that time spent watching television (OR 1.646; 95% CI 1.161-2.333, p = 0.005) and physical activity (OR 0.953, 95% CI 0.924-0.988, p = 0.003) remained independently causally associated with gallstones.

CONCLUSIONS

Prolonged sitting increases the risk of gallstones, whereas recreational activity reduces the risk. These findings need to be verified in further prospective cohort studies with larger sample sizes and longer follow-up periods.

Evaluation for causal effects of socioeconomic traits on risk of female genital prolapse (FGP): a multivariable Mendelian randomization analysis

BACKGROUND

Although observational studies have established some socioeconomic traits to be independent risk factors for pelvic organ prolapse (POP), they can not infer causality since they are easily biased by confounding factors and reverse causality. Moreover, it remains ambiguous which one or several of socioeconomic traits play predominant roles in the associations with POP risk. Mendelian randomization (MR) overcomes these biases and can even determine one or several socioeconomic traits predominantly accounting for the associations.

OBJECTIVE

We conducted a multivariable Mendelian randomization (MVMR) analysis to disentangle whether one or more of five categories of socioeconomic traits, "age at which full-time education completed (abbreviated as "EA")", "job involving heavy manual or physical work ("heavy work")", "average total household income before tax (income)", "Townsend deprivation index at recruitment (TDI)", and "leisure/social activities" exerted independent and predominant effects on POP risk.

METHODS

We first screened single-nucleotide polymorphisms (SNPs) as proxies for five individual socioeconomic traits and female genital prolapse (FGP, approximate surrogate for POP due to no GWASs for POP) to conduct Univariable Mendelian randomization (UVMR) analyses to estimate causal associations of five socioeconomic traits with FGP risk using IVW method as major analysis. Additionally, we conducted heterogeneity, pleiotropy, and sensitivity analysis to assess the robustness of our results. Then, we harvested a combination of SNPs as an integrated proxy for the five socioeconomic traits to perform a MVMR analysis based on IVW MVMR model.

RESULTS

UVMR analyses based on IVW method identified causal effect of EA (OR 0.759, 95%CI 0.629-0.916, p = 0.004), but denied that of the other five traits on FGP risk (all p > 0.05). Heterogeneity analyses, pleiotropy analyses, "leave-one-out" sensitivity analyses and MR-PRESSO adjustments did not detect heterogeneity, pleiotropic effects, or result fluctuation by outlying SNPs in the effect estimates of six socioeconomic traits on FGP risk (all p > 0.05). Further, MVMR analyses determined a predominant role of EA playing in the associations of socioeconomic traits with FGP risk based on both MVMR Model 1 (OR 0.842, 95%CI 0.744-0.953, p = 0.006) and Model 2 (OR 0.857, 95%CI 0.759-0.967, p = 0.012).

CONCLUSION

Our UVMR and MVMR analyses provided genetic evidence that one socioeconomic trait, lower educational attainment, is associated with risk of female genital prolapse, and even independently and predominantly accounts for the associations of socioeconomic traits with risk of female genital prolapse.

Insight into the Burden of Malignant Respiratory Tumors and their Relationship with Smoking Rates and Lead Contamination in Mexico

We aimed to report the results from the Global Burden of Disease Study 2019 related to respiratory malignant tumors (tracheal, bronchial, and lung) in Mexico. We also evaluated the relationship between the burden of these neoplasms and the proportion of daily smokers and total lead emissions in 2019. A cross-sectional analysis of ecological data was performed. The burden of these tumors was 152,189 disability-adjusted life-years (DALYs), and years of life lost (YLL) contributed to 99% of them. The highest DALYs rates (per 100,000) were observed in the states of Sinaloa, Chihuahua, Baja California Sur, Sonora, and Nayarit. We documented a linear relationship between the DALYs rates and the prevalence of daily smokers (β = 8.50, 95% CI 1.58-15.38) and the total lead emissions (tons/year: β = 4.04, 95% CI 0.07-8.01). If later replicated, our study would provide insight into the major relevance of regulating tobacco use and the activities associated with the production of lead dust and other hazardous contaminants.

The association between circulating docosahexaenoic acid and lung cancer: A Mendelian randomization study

BACKGROUND

Lung cancer is a malignant tumor with a high incidence, it is vital to identify modifiable and avoidable risk factors for primary prevention, which can significantly lower the risk of cancer by preventing exposure to hazards and altering risky behavior. Some observational studies suggest that an increase in docosahexaenoic acid (DHA) consumption can reduce lung cancer risk. However, interpretation of these observational findings is difficult due to residual confounding or reverse causality. To evaluate the link between DHA and lung cancer, we have undertaken this analysis to examine the causal association between DHA and the risk of lung cancer using a two-sample Mendelian randomization (MR) framework.

METHODS

We performed a two-sample MR analysis to evaluate the causal effect of plasma DHA levels on lung cancer risk. For the exposure data, we extracted genetic variants as instrumental variables (IVs) that are strongly associated with DHA from a large-scale genome-wide association study (GWAS). We obtained the corresponding effect estimates for IVs on the risk of lung cancer with 11,348 cases and 15,861 controls. Finally, we applied Mendelian randomization analysis to obtain preliminary MR results and performed sensitivity analyses to verify the robustness of our results.

RESULTS

According to the primary MR estimates and further sensitivity analyses, a higher serum DHA level was associated with a higher risk of lung cancer [OR = 1.159, 95% CI (1.04-1.30), P = 0.01]. For lung adenocarcinoma, the results also showed a close correlation between the DHA level and lung adenocarcinoma [OR = 1.277, 95% CI (1.09-1.50), P = 0.003], but it was not statistically significant for squamous cell carcinoma [OR = 1.071, 95% CI (0.89-1.29), P = 0.467].

CONCLUSIONS

Our study revealed that plasma DHA is positively associated with the risk of lung cancer overall, especially for lung adenocarcinoma. This study provides new information to develop dietary guidelines for primary lung cancer prevention.

Causal relationship between insomnia and tuberculosis: A bi-directional Mendelian randomization analysis

Previous observational studies appear to have established a bi-directional association between sleep disorders and tuberculosis. However, their conclusions are prone to be biased by confounding effects and reverse causation due to the nature of observational studies. Mendelian randomization (MR) approach provides unconfounded estimates of causal effects and overcomes the limitations of observational studies. We performed a bi-directional MR analysis to clarify whether there existed a causal effect of insomnia on tuberculosis, or tuberculosis on insomnia. In forward-direction MR, we chose genome-wide significant (P < .5 × 10-8) and independent (r2 < 0.001) single-nucleotide polymorphisms (SNPs) as instrumental variants (IVs), then extracted effect estimates of these IVs in tuberculosis genome-wide association study (GWAS) dataset to explore causal effect of genetically proxied insomnia on tuberculosis using inverse variance-weighted (IVW), MR-Egger, and weighted median methods. Additionally, we examined robustness and pleiotropy of effect estimates by heterogeneity and sensitivity analysis. Similarly, we investigated causal effect of genetically proxied tuberculosis on insomnia in reverse-direction MR. We revealed no causal relationship between genetically proxied insomnia and tuberculosis using 15 SNPs in forward-direction MR (IVW OR 5.305 [0.100-281.341], P = .410) and reverse-direction MR analysis (ORs and P values were not applicable due to no eligible SNPs in GWAS), with insignificant heterogeneity (Q = 22.6, I2 < 0.001, P = .066) and pleiotropy (intercept = 0.032, SE = 0.057, P = .592) in effect estimates. Our bi-directional MR analysis affirms no causal effect of insomnia on tuberculosis, or tuberculosis on insomnia.

Cancer in twin pairs discordant for smoking: The Nordic Twin Study of Cancer

The discordant twin pair study design is powerful to control for familial confounding. We employed this approach to investigate the associations of smoking with several cancers. The NorTwinCan study combines data from the Danish, Finnish, Norwegian and Swedish twin and cancer registries. Follow‐up started when smoking status was determined and ended at cancer diagnosis confirmed by information in the cancer registry, death or end of follow‐up. We classified the participants as never (n = 59 093), former (n = 21 168) or current (n = 47 314) smokers. We pooled data from twin pairs where one co‐twin was diagnosed with any of the following tobacco‐related cancers: esophagus, kidney, larynx, liver, oral cavity, pancreas, pharynx or urinary bladder, while their co‐twin had none of those. Lung cancer was included in further analysis. We used Cox regression allowing for pair‐specific baseline functions to estimate hazard ratios (HRs) with 95% confidence intervals (CIs). For tobacco‐related cancer sites, we recorded 7379 cases during median 27 years of follow‐up. The analyses based on individual twins showed that former (HR 1.31, 95% CI: 1.17‐1.48) and current (HR 2.14 [1.95‐2.34]) smokers are at increased risk to develop one of cancers listed above, compared to never smokers. Among 109 monozygotic twin pairs discordant for cancer and smoking, the HR was 1.85 (95% CI: 1.15‐2.98) among current smokers and 1.69 (1.00‐2.87) among former smokers when compared to their never smoking co‐twin. Thus, associations of smoking with several cancers were replicated for discordant identical twin pairs. Analyses based on genetically informative data provide evidence consistent with smoking causing multiple cancers.

Causal associations between dietary antioxidant vitamin intake and lung cancer: A Mendelian randomization study

Background

Oxidative stress is currently considered to be closely related to the occurrence of respiratory tumors, especially lung cancer. Many observational studies have shown that increased antioxidant intake can reduce the risk of lung cancer, but the results are still controversial. Therefore, we performed a two-sample Mendelian randomized (MR) analysis to clarify the causal relationship between antioxidant vitamins and lung cancer.

Methods

To assess the causal effect of dietary antioxidant vitamin intake on lung cancer, we conducted a two-sample MR analysis and we extracted single-nucleotide polymorphisms (SNPs) that are associated with antioxidants from genome-wide association studies (GWASs) of the UK biobank. We gathered summary data for lung cancer from the International Lung Cancer Consortium (ILCCO), including 11,348 cases and 15,861 controls, and applied the inverse-variance weighted (IVW) method as the primary MR analysis, and performed a sensitivity analysis to verify the results.

Results

The results showed that higher dietary retinol intake was causally associated with lung cancer overall [odds ratio (OR) = 1.844, 95% CI, 1.359-2.502, p = 0.00009], squamous cell lung cancer (OR = 2.162, 95% CI, 1.117-4.183, p = 0.022), and lung adenocarcinoma (OR = 1.706, 95% CI, 1.084-2.685, p = 0.021). Additionally, carotene was positively correlated with lung adenocarcinoma (OR = 1.510, 95% CI, 1.002-2.276, p = 0.049). However, there was a non-significant relationship between the intake of other dietary antioxidants (vitamin C and vitamin E) and lung cancer.

Conclusion

Our research showed that dietary retinol intake has an adverse impact on lung cancer, and carotene might increase the risk of adenocarcinoma. This highlights the importance of revealing the underlying mechanisms of dietary antioxidant vitamins in lung cancer and delivers an important health message that dietary antioxidant vitamin intake may not be necessary for the prevention of lung cancer. It also provides a basis for future research.

Identifying modifiable risk factors of lung cancer: Indications from Mendelian randomization

Background

Lung cancer is the major cause of mortality in tumor patients. While its incidence rate has recently declined, it is still far from satisfactory and its potential modifiable risk factors should be explored.

Methods

We performed a two-sample Mendelian randomization (MR) study to investigate the causal relationship between potentially modifiable risk factors (namely smoking behavior, alcohol intake, anthropometric traits, blood pressure, lipidemic traits, glycemic traits, and fasting insulin) and lung cancer. Besides, a bi-directional MR analysis was carried out to disentangle the complex relationship between different risk factors. Inverse-variance weighted (IVW) was utilized to combine the estimation for each SNP. Cochrane’s Q value was used to evaluate heterogeneity and two methods, including MR-Egger intercept and MR-PRESSO, were adopted to detect horizontal pleiotropy.

Results

Three kinds of smoking behavior were all causally associated with lung cancer. Overall, smokers were more likely to suffer from lung cancer compared with non-smokers (OR = 2.58 [1.95, 3.40], p-value = 2.07 x 10⁻¹¹), and quitting smoking could reduce the risk (OR = 4.29[2.60, 7.07], p-value = 1.23 x 10⁻⁸). Furthermore, we found a dose-response relationship between the number of cigarettes and lung cancer (OR = 6.10 [5.35, 6.96], p-value = 4.43x10^-161). Lower HDL cholesterol could marginally increase the risk of lung cancer, but become insignificant after Bonferroni correction (OR = 0.82 [0.68, 1.00], p-value = 0.045). In addition, we noted no direct causal relationship between other risk factors and lung cancer. Neither heterogeneity nor pleiotropy was observed in this study. However, when treating the smoking behavior as the outcome, we found the increased BMI could elevate the number of cigarettes per day (beta = 0.139[0.104, 0.175], p-value = 1.99x10^-14) and a similar effect was observed for the waist circumference and hip circumference. Additionally, the elevation of SBP could also marginally increase the number of cigarettes per day (beta = 0.001 [0.0002, 0.002], p-value = 0.018).

Conclusion

Smoking behavior might be the most direct and effective modifiable way to reduce the risk of lung cancer. Meanwhile, smoking behavior can be affected by other risk factors, especially obesity.