Elucidation of causal direction between asthma and obesity: a bi-directional Mendelian randomization study

Trends in disease burden and risk factors of asthma from 1990 to 2019 in Belt and Road Initiative countries: evidence from the Global Burden of Disease Study 2019

This study outlines asthma burden trends across age, sex, regions and risk factors in 'Belt and Road' (B&R) countries from 1990 to 2019 using the Global Burden of Disease Study 2019 data. Incidence, mortality, prevalence, years lived with disability (YLDs), disability-adjusted life years (DALYs) and risk factors for asthma were measured. India, China and Indonesia bore the heaviest burden in 2019. Despite the significant decline in the average annual percent change for age-standardized mortality and years of life lost from 1990 to 2019, increases were observed in several East Asian, Central Asian, North African and Middle Eastern countries between 2010 and 2019. For both sexes, YLDs decreased in most B&R countries but increased in Montenegro, Saudi Arabia, Armenia, Vietnam and Oman. YLDs in Georgia, the United Arab Emirates and Albania increased in males but decreased in females. YLDs increased for those aged <15 years in Central Asia and Europe, while China's 50-74-year age group showed the lowest YLD change. High body mass index (BMI) led to increased YLDs in East, Central and Southeast Asia; North Africa; and the Middle East. Conclusively, asthma burden varies significantly by country. Tailoring control efforts to specific regions, sex and high BMI could enhance asthma management.

Association of psoriasis with allergic multimorbidity of asthma, rhinitis, and eczema among adolescents: a cross-sectional study

BACKGROUND

Associations between psoriasis and allergic diseases (asthma, rhinitis, and eczema) in children have been reported in a limited number of studies, and the association between psoriasis and multimorbidity (co-occurrence) of allergic diseases remains unclear. Hence, this study aimed to assess the association between psoriasis and the co-occurrence of asthma, rhinitis, and eczema in adolescents.

METHODS

This school-based cross-sectional study enrolled adolescents (n = 3,864) aged 11-14 years. Parents completed a questionnaire on doctor-diagnosed psoriasis as well as symptoms and clinical history of asthma, rhinitis, and eczema. Eight nonoverlapping groups comprising single and co-occurring current (past 12 months) asthma, rhinitis, and eczema were identified. A multinomial logistic regression model was used to estimate the adjusted odds ratios (aOR) and 95% confidence intervals (CI).

RESULTS

In the analytical sample (n = 3,710; 1,641 male and 2,069 female participants), 3.5% reported doctor-diagnosed psoriasis, and 15.7%, 15.0%, and 10.3% had current asthma, rhinitis, and eczema symptoms, respectively. Doctor-diagnosed psoriasis was associated with "asthma only" (aOR = 2.11, 95% CI: 1.15-3.89), "eczema only" (6.65, 4.11-10.74), "asthma + eczema" (5.25, 2.36-11.65), "rhinitis + eczema" (3.60, 1.07-12.15), and "asthma + rhinitis + eczema" (7.38, 2.93-18.58). Doctor-diagnosed psoriasis was not statistically significantly associated with "rhinitis only" (1.42, 0.71--2.84) and "asthma + rhinitis" (1.78, 0.69-4.56).

CONCLUSION

Our findings indicate that psoriasis is associated with the co-occurrence of allergic diseases among adolescents. However, further studies are required to investigate which biological mechanisms may be shared between psoriasis and allergic diseases.

Factors associated with having uncontrolled asthma in rural Appalachia

BACKGROUND

Chronic respiratory disease disproportionately affects residents of Appalachia, particularly those residing in Central Appalachia. Asthma is particularly burdensome to Central Appalachian residents regarding cost and disability. Improving our understanding of how to mitigate these burdens requires understanding the factors influencing asthma control among individuals with asthma living in Central Appalachia, specifically rural Kentucky.

METHODS

This community-based, cross-sectional epidemiologic study used survey data to identify characteristics associated with uncontrolled and controlled asthma. The designation of "uncontrolled asthma" was based on a self-report of ≥ 2 asthma exacerbations in the past year. Individuals with ≤ 1 or no exacerbations were considered to have controlled asthma. Chi-square or Fisher exact tests assessed the association between categorical variables and asthma control categories. Logistic regression was conducted to determine the impact of factors on the likelihood of uncontrolled asthma.

RESULTS

In a sample of 211 individuals with self-reported asthma, 29% (n = 61, 46 females) had uncontrolled asthma. Predictors of uncontrolled asthma included depression (odds ratio 2.61, 95% CI 1.22-5.61, p = .014) and living in multi-unit housing (odds ratio 4.99, 95% CI 1.47-16.96, p = .010) when controlling for age, sex, financial status, and occupation. Being overweight or obese was not a predictor of uncontrolled asthma. Physical activity and BMI did not predict the likelihood of uncontrolled asthma.

CONCLUSION

This study highlights significant challenges rural communities in Appalachian Kentucky face in managing asthma. Factors like depression, housing conditions, and a lack of self-management strategies play pivotal roles in asthma control in this population.

The association between waist circumference and adult asthma attack using nationally representative samples

AIMS

This study aims to explore the relationship between waist circumference and asthma attack in adults.

METHODS

In this cross-sectional study, we analysed data from 5,530 U.S. adults diagnosed with asthma. Participants were categorized into two groups based on their experience of asthma attacks: with or without asthma attacks. We employed adjusted weighted logistic regression models, weighted restricted cubic splines, subgroup and sensitivity analyses to assess the association between waist circumference and asthma attack.

RESULTS

The median age of all participants was 43 years, and the median waist circumference was 98.9 cm, with a median BMI was 28.50 kg/m2. Participants in the asthma attack group had significantly higher waist circumferences than those in the non-attack group (P < 0.001). After full adjustment for body mass index-defined obesity, age, gender, race, education levels, poverty income ratio levels, smoking status, and metabolic syndrome, every 5 cm increase in waist circumference exhibited a 1.06 times higher likelihood of asthma attack probability. The weighted restricted cubic spline analysis demonstrated an increased risk of asthma attacks with rising waist circumference. Subgroup analyses confirmed this relationship across various groups differentiated by gender, age, and smoking status. When applying a stricter definition of asthma attack, the weighted logistic regression models showed robust association between waist circumference and asthma attack.

CONCLUSION

Waist circumference is an independent predictor of asthma attacks. Our findings underscore the importance of waist circumference measurement in evaluating the risk of asthma attacks.

The associations between asthma and common comorbidities: a comprehensive Mendelian randomization study

Background

Asthma is a chronic respiratory disease and is often associated with multiple comorbidities. The causal relationship between asthma and these comorbidities is still unclear. This study aimed to investigate the association between genetically predicted asthma and common comorbidities.

Methods

After searching PubMed and GWAS summary statistics, we identified 26 comorbidities of asthma. The causal relationship between asthma and comorbidities was assessed in two independent GWASs by bidirectional Mendelian randomization, followed by validation of the results using a multivariate Mendelian randomization analysis and several sensitivity analyses.

Results

In the bidirectional Mendelian randomization analysis, chronic sinusitis [odds ratio (OR) = 1.54, p = 1.40 × 10-5], atopic dermatitis (OR = 1.36, p = 9.37 × 10-21), allergic conjunctivitis (OR = 2.07, p = 4.32 × 10-6), and allergic rhinitis (OR = 1.53, p = 5.20 × 10-6) were significantly associated with increased asthma risk. Hyperthyroidism (OR = 1.12, p = 0.04) had a potential increased risk for asthma. For the reverse direction, asthma showed significant associations with an increased risk of chronic obstructive pulmonary disease (OR = 1.24, p = 2.25 × 10-9), chronic sinusitis (OR = 1.61, p = 5.25 × 10-21), atopic dermatitis (OR = 2.11, p = 1.24 × 10-24), allergic conjunctivitis (OR = 1.65, p = 6.66 × 10-35), allergic rhinitis (OR = 1.90, p = 2.38 × 10-57), and a potential higher risk of allergic urticaria (OR = 1.25, p = 0.003).

Conclusion

This study suggested a significant bidirectional association of chronic sinusitis, atopic dermatitis, allergic conjunctivitis, and allergic rhinitis with asthma. In addition, hyperthyroidism was associated with an increased risk of asthma and asthma increased the risk of chronic obstructive pulmonary disease and allergic urticaria.

Age at menarche and asthma onset among US girls and women: findings from NHANES, 2001-2018

PURPOSE

To quantitatively estimate the association of age at menarche with the risk of childhood- and adult-onset asthma separately.

METHODS

A retrospective cohort study of 24,282 US girls and women was conducted using continuous National Health and Nutrition Examination Survey (NHANES) data from 2001 to 2018, and Cox proportional hazards regression models with censoring ages of 19 and 79 years were employed to separately estimate hazard ratios of childhood- and adult-onset asthma associated with age at menarche.

RESULTS

Each one-year increase in age at menarche was significantly associated with a 16% (hazard ratio [HR] = 0.84; 95% confidence interval [CI]: 0.77-0.91) decrease in the risk of childhood-onset asthma. Compared with age at menarche of 12-14 years, we observed a 56% (HR = 1.56; 95% CI: 1.19-2.04) increased risk of childhood-onset asthma for early menarche (age at menarche < 12 years) and a 40% (HR = 0.60; 95% CI: 0.32-1.10) decreased risk for late menarche (age at menarche ≥ 15 years). No significant association was noted between age at menarche and adult-onset asthma.

CONCLUSIONS

Early menarche may represent a risk factor for childhood-onset asthma, which indicates the need for timely and effective management of individuals with early menarche to prevent asthma.

The Medical Burden of Obesity and Overweight in the US Military: Association of BMI with Clinically Diagnosed Medical Conditions in United States Military Service Members

BACKGROUND

A high BMI is associated with various medical conditions, notably type 2 diabetes, cardiovascular disease, and mental health disorders. In the US military, BMI increased linearly between 1975 and 2015.

OBJECTIVE

This cross-sectional study investigated the associations between BMI and a comprehensive range of clinically diagnosed medical conditions (CDMCs) in US military service members (SMs).

METHODS

A stratified random sample of SMs (n=26,177) completed an online questionnaire reporting their height, weight, and demographic/lifestyle characteristics. Medical conditions for 6 mo before questionnaire completion were obtained from a comprehensive military electronic medical surveillance system and grouped into 39 CDMCs covering both broad (largely systemic) and specific medical conditions. BMI was calculated as weight/height2 (kg/m2). The prevalence of CDMCs was compared among normal weight (<25.0 kg/m2), overweight (25.0-29.9 kg/m2), and obese (≥30 kg/m2) SMs.

RESULTS

After multivariable adjustment for demographic/lifestyle characteristics, higher BMI was associated with higher odds of a diagnosed medical condition in 30 of 39 CDMCs, with all 30 displaying dose-response relationships. The 5 major CDMCs with the largest odds ratios comparing obese to normal weight were endocrine/nutritional/metabolic diseases (OR=2.67, 95%CI=2.24-3.15), nervous system diseases (odds ratio [OR]=2.59, 95%CI=2.32-2.90), circulatory system diseases (OR=2.56, 95%CI=2.15-3.06), musculoskeletal system diseases (OR=1.92, 95%CI=1.76-2.09), and mental/behavioral disorders (OR=1.69, 95%CI=1.51-1.90). Compared with normal weight SMs, overweight or obese SMs had a higher number of CDMCs (1.8±1.9 vs. 2.0±2.0 and 2.5±2.3, mean ± standard deviation, respectively, P<0.01).

CONCLUSIONS

In a young, physically active population, higher BMI was associated with a host of medical conditions, even after adjustment for demographic/lifestyle characteristics. The US Department of Defense should improve nutrition education and modify other factors that contribute to overweight and obesity. This study demonstrates that the medical burden of obesity is substantial in overweight and obese SMs.

Obesity and risk for respiratory diseases: a Mendelian randomization study

Background

No existing comprehensive Mendelian randomization studies have focused on how obesity affects respiratory diseases.

Methods

BMI and waist circumference, mainly from the UK Biobank, and 35 respiratory diseases from the FinnGen Biobank were subjected to Mendelian randomization analyses. In this study, the inverse variance weighting method was used as the predominant analysis method and was complemented by MR-Egger and weighted median methods. Horizontal pleiotropy and potential outliers were detected by employing the MR-PRESSO method.

Results

This study indicated that obesity rises the possibility of acute upper respiratory infections (BMI: OR=1.131, p<0.0001; WC: OR=1.097, p=0.00406), acute sinusitis (BMI: OR=1.161, p=0.000262; WC: OR=1.209, p=0.000263), acute pharyngitis (WC: OR=1.238, p=0.0258), acute laryngitis and tracheitis (BMI: OR=1.202, p=0.0288; WC: OR=1.381, p=0.00192), all influenza (BMI: OR=1.243, p=0.000235; WC: OR=1.206, p=0.0119), viral pneumonia (WC: OR=1.446, p=0.000870), all pneumoniae (BMI: OR=1.174, p <0.0001; WC: OR=1.272, p <0.0001), bacterial pneumoniae (BMI: OR=1.183, p=0.000290; WC: OR=1.274, p<0.0001), acute bronchitis (BMI: OR=1.252, p <0.0001; WC: OR=1.237, p=0.000268), acute unspecified lower respiratory infection (BMI: OR=1.303, p=0.000403), chronic tonsils and adenoids diseases (BMI: OR=1.236, p <0.0001; WC: OR=1.178, p=0.000157), chronic laryngotracheitis and laryngitis (WC: OR=1.300, p=0.00785), COPD (BMI: OR=1.429, p <0.0001; WC: OR=1.591, p <0.0001), asthma (BMI: OR=1.358, p <0.0001; WC: OR=1.515, p <0.0001), necrotic and suppurative conditions of lower respiratory tract (WC: OR=1.405, p=0.0427), pleural effusion (BMI: OR=1.277, p=0.00225; WC: OR=1.561, p<0.0001), pleural plaque (BMI: OR=1.245, p=0.0312), other diseases of the respiratory system (BMI: OR=1.448, p <0.0001; WC: OR=1.590, p <0.0001), and non-small cell lung cancer (BMI: OR=1.262, p=0.00576; WC: OR=1.398, p=0.00181). This study also indicated that obesity decreases the possibility of bronchiectasis (BMI: OR=0.705; p=0.00200).

Conclusion

This study revealed that obesity increases the risk of the majority of respiratory diseases (including 20 of all 35 respiratory diseases) and that obesity decreases the risk of bronchiectasis.

Mendelian Randomization Analysis Reveals a Complex Genetic Interplay among Atopic Dermatitis, Asthma, and Gastroesophageal Reflux Disease

Rationale: Gastroesophageal reflux disease (GERD) is commonly associated with atopic disorders, but cause-effect relationships remain unclear. Objectives: We applied Mendelian randomization analysis to explore whether GERD is causally related to atopic disorders of the lung (asthma) and/or skin (atopic dermatitis [AD]). Methods: We conducted two-sample bidirectional Mendelian randomization to infer the magnitude and direction of causality between asthma and GERD, using summary statistics from the largest genome-wide association studies conducted on asthma (Ncases = 56,167) and GERD (Ncases = 71,522). In addition, we generated instrumental variables for AD from the latest population-level genome-wide association study meta-analysis (Ncases = 22,474) and assessed their fidelity and confidence of predicting the likely causal pathway(s) leading to asthma and/or GERD. Measurements and Main Results: Applying three different methods, each method revealed similar magnitude of causal estimates that were directionally consistent across the sensitivity analyses. Using an inverse variance-weighted method, the largest effect size was detected for asthma predisposition to AD (odds ratio [OR], 1.46; 95% confidence interval [CI], 1.34-1.59), followed by AD to asthma (OR, 1.34; 95% CI, 1.24-1.45). A significant association was detected for genetically determined asthma on risk of GERD (OR, 1.06; 95% CI, 1.03-1.09) but not genetically determined AD on GERD. In contrast, GERD equally increased risks of asthma (OR, 1.21; 95% CI, 1.09-1.35) and AD (OR, 1.21; 95% CI, 1.07-1.37). Conclusions: This study uncovers previously unrecognized causal pathways that have clinical implications in European-ancestry populations: 1) asthma is a causal risk for AD, and 2) the predisposition to AD, including asthma, can arise from specific pathogenic mechanisms manifested by GERD.

Relationship among genetic variants, obesity traits and asthma in the Taiwan Biobank

BACKGROUND AND OBJECTIVE

Obesity and asthma impose a heavy health and economic burden on millions of people around the world. The complex interaction between genetic traits and phenotypes caused the mechanism between obesity and asthma is still vague. This study investigates the relationship among obesity-related polygenic risk score (PRS), obesity phenotypes and the risk of having asthma.

METHODS

This is a matched case-control study, with 4 controls (8288 non-asthmatic) for each case (2072 asthmatic). Data were obtained from the 2008-2015 Taiwan Biobank Database and linked to the 2000-2016 National Health Insurance Research Database. All participants were ≥30 years old with no history of cancer and had a complete questionnaire, as well as physical examination, genome-wide single nucleotide polymorphisms and clinical diagnosis data. Environmental exposure, PM_2.5, was also considered. Multivariate adjusted ORs and 95% CIs were calculated using conditional logistic regression stratified by age and sex. Mediation analysis was also assessed, using a generalised linear model.

RESULTS

We found that the obese phenotype was associated with significantly increased odds of asthma by approximately 26%. Four obesity-related PRS, including body mass index (OR=1.07 (1.01-1.13)), waist circumference (OR=1.10 (1.04-1.17)), central obesity as defined by waist-to-height ratio (OR=1.09 (1.03-1.15)) and general-central obesity (OR=1.06 (1.00-1.12)), were associated with increased odds of asthma. Additional independent risk factors for asthma included lower educational level, family history of asthma, certain chronic diseases and increased PM_2.5 exposure. Obesity-related PRS is an indirect risk factor for asthma, the link being fully mediated by the trait of obesity.

CONCLUSIONS

Obese phenotypes and obesity-related PRS are independent risk factors for having asthma in adults in the Taiwan Biobank. Overall, genetic risk for obesity increases the risk of asthma by affecting the obese phenotype.

The bidirectional association between wheezing and obesity during adolescence and the beginning of adulthood in the 1993 birth cohort, Pelotas, Brazil

Objective: To analyze the bidirectional association between wheezing and obesity during adolescence and the beginning of adulthood in a cohort in southern Brazil. Methods: This prospective longitudinal study used data from the 1993 birth cohort in Pelotas, Brazil. The following outcome variables were measured at 22 years of age: self-reported wheezing during the last 12 months and obesity (BMI = 30 kg/m2). The following exposure variables were measured at ages 11, 15, and 18: self-reported wheezing (no wheezing or symptom presentation in 1, 2, or 3 follow-ups) and obesity (non-obese or obese in 1, 2, or 3 follow-ups). Crude and adjusted logistical regression stratified by sex were used in the analyses. The reference category was defined as participants who presented no wheezing or obesity. Results: A total of 3,461 participants had data on wheezing and 3,383 on BMI. At 22 years of age, the prevalence of wheezing was 10.1% (95%CI: 9.1; 11.2), and obesity, 16.2% (95%CI: 15.0; 17.6). In females, the presence of wheezing in two follow-ups revealed a 2.22-fold (95%CI: 1.36; 3.61) greater chance of developing obesity at 22 years of age. Meanwhile, the presence of obesity in two follow-ups resulted in a 2.03-fold (95%IC: 1.05; 3.92) greater chance of wheezing at 22 years of age. No associations were found between wheezing and obesity in males. Conclusions: The obtained data suggest a possible positive bidirectional association between wheezing and obesity, with greater odds ratios in the wheezing to obesity direction in females and in the category of occurrence of exposure in two follow-ups.

Causal risk factors for asthma in Mendelian randomization studies: A systematic review and meta-analysis

BACKGROUND

Several risk factors for asthma have been proposed; however, the causality of these associations is sometimes unclear. Mendelian randomization is a powerful epidemiological approach that can help elucidate the causality of risk factors. The aim of the present study was to identify causal risk factors for asthma through Mendelian Randomization studies.

METHODS

A systematic search of PubMed and EMBASE was conducted, to identify studies investigating risk factors for asthma or respiratory allergies through Mendelian Randomization. When two or more studies investigated the same risk factor a meta-analysis was conducted. Of 239 studies initially identified, 41 were included.

RESULTS

A causal association between adiposity and adult asthma risk was found in 10 out of 12 studies with a summary risk ratio of 1.05 per kg/m2 increase in BMI (95% CI: 1.03-1.07). Puberty timing (n = 3), alcohol (n = 2), and linoleic acid (n = 1) had causal effects on asthma risk, while vitamins/minerals (n = 6) showed no consistent effect on asthma. The effect of smoking on adult asthma conflicted between studies. Several of the significant associations of asthma with immune related proteins (n = 5) and depression (n = 2) investigated through multiple traits analyses could generally benefit from replications in independent datasets.

CONCLUSION

This systematic review and meta-analysis found evidence for causal effects of adiposity, puberty timing, linoleic acid, alcohol, immune related proteins, and depression on risk of asthma.

Obesity-related biomarkers underlie a shared genetic architecture between childhood body mass index and childhood asthma

Obesity and asthma are both common diseases with high population burden worldwide. Recent genetic association studies have shown that obesity is associated with asthma in adults. The relationship between childhood obesity and childhood asthma, and the underlying mechanisms linking obesity to asthma remain to be clarified. In the present study, leveraging large-scale genetic data from UK biobank and several other data sources, we investigated the shared genetic components between body mass index (BMI, n = 39620) in children and childhood asthma (n_case = 10524, n_control = 373393). We included GWAS summary statistics for nine obesity-related biomarkers to evaluate potential biological mediators underlying obesity and asthma. We found a genetic correlation (Rg = 0.10, P = 0.02) between childhood BMI and childhood asthma, whereas the genetic correlation between adult BMI (n = 371541) and childhood asthma was null (Rg = -0.03, P = 0.21). Genomic structural equation modeling analysis further provided evidence that the genetic effect of childhood BMI on childhood asthma (standardized effect size 0.17, P = 0.009) was not driven by the genetic component of adult BMI. Bayesian colocalization analysis identified a shared causal variant rs12436181 that was mapped to gene AMN using gene expression data in lung tissue. Mendelian randomization showed that the odds ratio of childhood asthma for one standard deviation higher of childhood BMI was 1.13 (95% confidence interval: 0.96-1.34). A systematic survey of obesity-related biomarkers showed that IL-6 and adiponectin are potential biological mediators linking obesity and asthma in children. This large-scale genetic study provides evidence that unique childhood obesity pathways could lead to childhood asthma. The findings shed light on childhood asthma pathogenic mechanisms and prevention.

Association of weight change patterns across adulthood with incident asthma: a retrospective cohort study

This study aimed to investigate the relationship between weight change patterns across adulthood and the risk of incident asthma later in life using data from the National Health and Nutrition Examination Survey (NHANES) 2001-2018. In this retrospective cohort study, asthma was defined by self-report questionnaires, and age at diagnosis was used to estimate the time of asthma onset. Based on BMI at 25 years old (young adulthood) and BMI at 10 years before the survey (middle adulthood), patterns of weight change were divided into five categories including stable normal, non-obese to obese, obese to non-obese, maximum overweight and stable obese. A total of 27,359 participants (female 13,582, 49.6%) were enrolled in this study and during a mean follow-up of 9.8 years, 1035 subjects occurred asthma. After adjusting for age, gender, race, education, family income and smoking status, participants changing from non-obese to obese, stable obese had significantly higher risks of incident asthma than those with normal weight during adulthood (HR1.70, 95% CI 1.35-2.15, P < 0.0001; HR 1.66, 95% CI 1.21-2.19 P = 0.0019, respectively). The findings suggested that maintaining normal weight during adulthood may be important for preventing incident asthma in later life.

Burden of rare coding variants reveals genetic heterogeneity between obese and non-obese asthma patients in the African American population

Background

Asthma is a complex condition largely attributed to the interactions among genes and environments as a heterogeneous phenotype. Obesity is significantly associated with asthma development, and genetic studies on obese vs. non-obese asthma are warranted.

Methods

To investigate asthma in the minority African American (AA) population with or without obesity, we performed a whole genome sequencing (WGS) study on blood-derived DNA of 4289 AA individuals, included 2226 asthma patients (1364 with obesity and 862 without obesity) and 2006 controls without asthma. The burden analysis of functional rare coding variants was performed by comparing asthma vs. controls and by stratified analysis of obese vs. non-obese asthma, respectively.

Results

Among the top 66 genes with P < 0.01 in the asthma vs. control analysis, stratified analysis by obesity showed inverse correlation of natural logarithm (LN) of P value between obese and non-obese asthma (r = − 0.757, P = 1.90E−13). Five genes previously reported in a genome-wide association study (GWAS) on asthma, including TSLP, SLC9A4, PSMB8, IGSF5, and IKZF4 were demonstrated association in the asthma vs. control analysis. The associations of IKZF4 and IGSF5 are only associated with obese asthma; and the association of SLC9A4 is only observed in non-obese asthma. In addition, the association of RSPH3 (the gene is related to primary ciliary dyskinesia) is observed in non-obese asthma.

Conclusions

These findings highlight genetic heterogeneity between obese and non-obese asthma in patients of AA ancestry.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-022-02039-0.

Robust inference of bi-directional causal relationships in presence of correlated pleiotropy with GWAS summary data

To infer a causal relationship between two traits, several correlation-based causal direction (CD) methods have been proposed with the use of SNPs as instrumental variables (IVs) based on GWAS summary data for the two traits; however, none of the existing CD methods can deal with SNPs with correlated pleiotropy. Alternatively, reciprocal Mendelian randomization (MR) can be applied, which however may perform poorly in the presence of (unknown) invalid IVs, especially for bi-directional causal relationships. In this paper, first, we propose a CD method that performs better than existing CD methods regardless of the presence of correlated pleiotropy. Second, along with a simple but yet effective IV screening rule, we propose applying a closely related and state-of-the-art MR method in reciprocal MR, showing its almost identical performance to that of the new CD method when their model assumptions hold; however, if the modeling assumptions are violated, the new CD method is expected to better control type I errors. Notably bi-directional causal relationships impose some unique challenges beyond those for uni-directional ones, and thus requiring special treatments. For example, we point out for the first time several scenarios where a bi-directional relationship, but not a uni-directional one, can unexpectedly cause the violation of some weak modeling assumptions commonly required by many robust MR methods. We also offer some numerical support and a modeling justification for the application of our new methods (and more generally MR) to binary traits. Finally we applied the proposed methods to 12 risk factors and 4 common diseases, confirming mostly well-known uni-directional causal relationships, while identifying some novel and plausible bi-directional ones such as between body mass index and type 2 diabetes (T2D), and between diastolic blood pressure and stroke.

Mendelian Randomization: A Review of Methods for the Prevention, Assessment, and Discussion of Pleiotropy in Studies Using the Fat Mass and Obesity-Associated Gene as an Instrument for Adiposity

Pleiotropy assessment is critical for the validity of Mendelian randomization (MR) analyses, and its management remains a challenging task for researchers. This review examines how the authors of MR studies address bias due to pleiotropy in practice. We reviewed Pubmed, Medline, Embase and Web of Science for MR studies published before 21 May 2020 that used at least one single-nucleotide polymorphism (SNP) in the fat mass and obesity-associated (FTO) gene as instrumental variable (IV) for body mass index, irrespective of the outcome. We reviewed: 1) the approaches used to prevent pleiotropy, 2) the methods cited to detect or control the independence or the exclusion restriction assumption highlighting whether pleiotropy assessment was explicitly stated to justify the use of these methods, and 3) the discussion of findings related to pleiotropy. We included 128 studies, of which thirty-three reported one approach to prevent pleiotropy, such as the use of multiple (independent) SNPs combined in a genetic risk score as IVs. One hundred and twenty studies cited at least one method to detect or account for pleiotropy, including robust and other IV estimation methods (n = 70), methods for detection of heterogeneity between estimated causal effects across IVs (n = 72), methods to detect or account associations between IV and outcome outside thought the exposure (n = 85), and other methods (n = 5). Twenty-one studies suspected IV invalidity, of which 16 explicitly referred to pleiotropy, and six incriminating FTO SNPs. Most reviewed MR studies have cited methods to prevent or to detect or control bias due to pleiotropy. These methods are heterogeneous, their triangulation should increase the reliability of causal inference.

Using Mendelian randomization as the cornerstone for causal inference in epidemiology

Mendelian randomization (MR) is attracting considerable critical attention. This paper aimed to explore the characteristics of the publications of MR, to reach an insight in this field and prospect the future trend. A bibliometric analysis was performed to identify published MR-related research. The articles were selected from the Web of Science Core Collection database. Excel 2019, VOSviewer 1.6.9, and CiteSpace 5.7.R3 were used to analyze the information. A total of 1783 papers of MR were identified, and the first included literature appeared in 2003. A total of 2829 institutions from 72 countries participated in the relevant research, while the UK contributed to 852 articles and were in a leading position. The most productive institution was the University of Bristol, and Smith GD who has posted the most articles (n=202) was also from there. The Int J Epidemiol (100 publications, 6861 citations) was the most prolific and high citation journal. Related topics of frontiers will still focus on coronary heart disease, diabetes, cancer, psychiatric disorder, body mass index, and lifestyle factors. We summarized the publication information of MR-related literature from 2003 to 2020, including country and institution of origin, authors, and publication journal. We analyzed former research hotspots in the field of MR and predicted future areas of interest. Exposures and outcomes detected in this paper will be the hotspots and frontiers of research in the next few years.

Obesity, Inflammation, and Severe Asthma: an Update

Purpose of Review

Obesity-associated difficult asthma continues to be a substantial problem and, despite a move to address treatable traits affecting asthma morbidity and mortality, it remains poorly understood with limited phenotype-specific treatments. The complex association between asthma, obesity, and inflammation is highlighted and recent advances in treatment options explored.

Recent Findings

Obesity negatively impacts asthma outcomes and has a causal link in the pathogenesis of adult-onset asthma. Imbalance in the adipose organ found in obesity favours a pro-inflammatory state both systemically and in airways. Obesity may impact currently available asthma biomarkers, and obesity-associated asthma specific biomarkers are needed. Whilst surgical weight loss interventions are associated with improvements in asthma control and quality of life, evidence for pragmatic conservative options are sparse. Innovative approaches tackling obesity-mediated airway inflammation may provide novel therapies.

Summary

The immunopathological mechanisms underlying obesity-associated asthma require further research that may lead to novel therapeutic options for this disease. However, weight loss appears to be effective in improving asthma in this cohort and focus is also needed on non-surgical treatments applicable in the real-world setting.

Asthma in Youth and Early-onset Type 2 Diabetes: A Nationwide Study of 1.72 Million Israeli Adolescents

BACKGROUND

The prevalence of both asthma and early-onset diabetes is on the rise; however, the association between them remains unclear. We examined a possible association of asthma at adolescence with type 2 diabetes in young adulthood.

METHODS

This is a nationwide, population-based study of 1 718 541 Israeli adolescents (57% males; mean age 17.3 years; range 16-19 years), examined before compulsory military service between 1992 and 2016, with data linked to the Israeli National Diabetes Registry. Asthma diagnosis and severity were determined by a board-certified pulmonologist and based on spirometry tests.

RESULTS

Type 2 diabetes developed in 58/9090 (0.64%), 507/97 059 (0.52%), 114/23 332 (0.49%), and 7095/1 589 060 (0.44%) persons with moderate-to-severe, mild, inactive, and no history of asthma, respectively, during a mean follow-up >13 years. The respective odds ratios (ORs) were 1.33 (95% CI, 1.02-1.74), 1.17 (1.06-1.28), and 1.09 (0.9-1.31), considering those without asthma history as the reference, in a model adjusted for birth year, sex, body mass index, and other sociodemographic variables. The association persisted when the analysis accounted for coexisting morbidities, and when persons without asthma, individually matched by age, sex, birth year, and body mass index were the reference. Both mild and moderate-to-severe asthma were associated with type 2 diabetes before age 35 years: ORs 1.18 (1.05-1.34) and 1.44 (1.05-2.00), respectively. The strength of the association was accentuated over time. The effect was unchanged when adjusted for oral and inhaled glucocorticoid use.

CONCLUSION

Adolescents with active asthma have higher risk to develop type 2 diabetes. This seems related to disease severity, independent of adolescent obesity status, apparent before age 35 years, and more pronounced in recent years.

Childhood patterns of overweight and wheeze and subsequent risk of current asthma and obesity in adolescence

BACKGROUND

Obesity and asthma in childhood often co-occur. Few studies have examined this relationship using repeated measures of body mass index (BMI) or asthma symptoms (such as wheeze).

OBJECTIVE

We compared two analytic approaches for repeated measures data to investigate this relationship.

METHODS

Our baseline sample consisted of 1277 children enrolled in a Boston-area cohort with BMI or wheeze at age 1 year and no missing covariates. We used latent class growth models (LCGM) and inverse probability weighting (IPW) of marginal structural models to examine the extent to which presence of overweight across childhood was associated with early adolescent current asthma, and conversely of repeated measures of wheeze across childhood with early adolescent obesity.

RESULTS

Using LCGM, a "persistent" childhood overweight class (vs "never") was associated with higher risk of asthma in early adolescence (RR 1.9; 95% CI 1.1, 3.0), while "persistent" childhood wheeze (vs "never") was associated with higher risk of obesity in early adolescence (RR 2.7; 95% CI 1.0, 6.4) after adjusting for baseline covariates. An IPW analysis treating childhood overweight and wheeze as time-varying exposures and adjusting for baseline and time-varying covariates resulted in weaker and less precise associations of "persistent" (vs "never") overweight with adolescent asthma (RR 1.3; 95% CI 0.3, 3.0), and of "persistent" (vs "never") wheeze with adolescent obesity (RR 2.3; 95% CI 0.4, 5.3).

CONCLUSION

Our point estimates from both approaches suggest an association between "persistent" childhood overweight and adolescent asthma, and between "persistent" childhood wheeze and adolescent obesity. LCGM results were stronger and more precise, whereas IPW results were less conclusive with wider 95% confidence intervals containing the null. The precision gained from LCGM may be at the expense of bias, and the use of both approaches helps to shed some light on this tradeoff.

Evaluating the Causal Association Between Educational Attainment and Asthma Using a Mendelian Randomization Design

Asthma is a common chronic respiratory disease. In the past 10 years, genome-wide association study (GWAS) has been widely used to identify the common asthma genetic variants. Importantly, these publicly available asthma GWAS datasets provide important data support to investigate the causal association of kinds of risk factors with asthma by a Mendelian randomization (MR) design. It is known that socioeconomic status is associated with asthma. However, it remains unclear about the causal association between socioeconomic status and asthma. Here, we selected 162 independent educational attainment genetic variants as the potential instruments to evaluate the causal association between educational attainment and asthma using large-scale GWAS datasets of educational attainment (n = 405,072) and asthma (n = 30,810). We conducted a pleiotropy analysis using the MR-Egger intercept test and the MR pleiotropy residual sum and outlier (MR-PRESSO) test. We performed an MR analysis using inverse-variance weighted, weighted median, MR-Egger, and MR-PRESSO. The main analysis method inverse-variance weighted indicated that each 1 standard deviation increase in educational attainment (3.6 years) could reduce 35% asthma risk [odds ratio (OR) = 0.65, 95% confidence interval (CI) 0.51–0.85, P = 0.001]. Importantly, evidence from other MR methods further supported this finding, including weighted median (OR = 0.55, 95% CI 0.38–0.80, P = 0.001), MR-Egger (OR = 0.48, 95% CI 0.16–1.46, P = 0.198), and MR-PRESSO (OR = 0.65, 95% CI 0.51–0.85, P = 0.0015). Meanwhile, we provide evidence to support that educational attainment protects against asthma risk dependently on cognitive performance using multivariable MR analysis. In summary, we highlight the protective role of educational attainment against asthma. Our findings may have public health applications and deserve further investigation.

Association Between Environmental Factors and Asthma Using Mendelian Randomization: Increased Effect of Body Mass Index on Adult-Onset Moderate-to-Severe Asthma Subtypes

Although asthma is one of the most common chronic diseases throughout all age groups, its etiology remains unknown, primarily due to its heterogeneous characteristics. We examined the causal effects of various environmental factors on asthma using Mendelian randomization and determined whether the susceptibility to asthma due to the causal effect of a risk factor differs between asthma subtypes, based on age of onset, severity of asthma, and sex. We performed Mendelian randomization analyses (inverse variance weighted, weighted median, and generalized summary-data-based Mendelian randomization) using UK Biobank data to estimate the causal effects of 69 environmental factors on asthma. Additional sensitivity analyses (MR-Egger regression, Cochran’s Q test, clumping, and reverse Mendelian randomization) were performed to ensure minimal or no pleiotropy. For confirmation, two-sample setting analyses were replicated using BMI SNPs that had been reported by a meta-genome-wide association study in Japanese and European (GIANT) populations and a genome-wide association study in control individuals from the UK Biobank. We found that BMI causally affects the development of asthma and that the adult-onset moderate-to-severe asthma subtype is the most susceptible to causal inference by BMI. Further, it is likely that the female subtype is more susceptible to BMI than males among adult asthma cases. Our findings provide evidence that obesity is a considerable risk factor in asthma patients, particularly in adult-onset moderate-to-severe asthma cases, and that weight loss is beneficial for reducing the burden of asthma.

Weight gain from early to middle adulthood increases the risk of incident asthma later in life in the United States: a retrospective cohort study

Background

Data describing the effects of weight change across adulthood on asthma are important for the prevention of asthma. This study aimed to investigate the association between weight change from early to middle adulthood and risk of incident asthma.

Methods

Using data from the National Health and Nutrition Examination Survey (NHANES), we performed a nationally retrospective cohort study of the U.S. general population. A total of 20,771 people aged 40–74 years with recalled weight at young and middle adulthood were included in the cohort. Four weight change groups were categorized: stable non-obesity, non-obesity to obesity, obesity to non-obesity, and stable obesity. Hazard ratios (HRs) and 95% confidence intervals (CIs) relating weight change to incident asthma over 10 years of follow-up were calculated using Cox models adjusting for covariates.

Results

Compared with the stable non-obesity group, the HRs of incident asthma were 1.63 (95% CI = 1.29 to 2.07, P < 0.001) for the non-obesity to obesity group, 1.41 (95% CI = 0.97 to 2.05, P = 0.075) for stable obesity group, and 1.21 (95% CI = 0.41 to 3.62, P = 0.730) for the obesity to non-obesity group. In addition, participants who gained more than 20 kg from young to middle adulthood had a HR of 1.53 (95% CI = 1.15 to 2.03, P = 0.004), compared with those whose weight remained stable (weight change within 2.5 kg).

Conclusions

Weight gain from early to middle adulthood was associated with higher risk of incident asthma as compared to those who maintained normal weight. Thus, maintaining normal weight throughout adulthood might be important for the primary prevention of adult-onset asthma.

Supplementary Information

The online version contains supplementary material available at 10.1186/s12931-021-01735-7.

Impaired Respiratory Health and Life Course Transitions From Health to Chronic Lung Disease

Primary prevention and interception of chronic lung disease are essential in the effort to reduce the morbidity and mortality caused by respiratory conditions. In this review, we apply a life course approach that examines exposures across the life span to identify risk factors that are associated with not only chronic lung disease but also an intermediate phenotype between ideal lung health and lung disease, termed "impaired respiratory health." Notably, risk factors such as exposure to tobacco smoke and air pollution, as well as obesity and physical fitness, affect respiratory health across the life course by being associated with both abnormal lung growth and lung function decline. We then discuss the importance of disease interception and identifying those at highest risk of developing chronic lung disease. This work begins with understanding and detecting impaired respiratory health, and we review several promising molecular biomarkers, predictive symptoms, and early imaging findings that may lead to a better understanding of this intermediate phenotype.

The Effects of Asthma on the Association Between Pulmonary Function and Obesity: A 16-Year Longitudinal Study

Background

Asthma and obesity are important public health issues around the world. Obesity is considered a risk factor associated with the severity and incidence of asthma. We investigated the relationships between poor pulmonary function (defined by forced vital capacity (FVC) and percentage of predicted FVC (FVC%)) and obesity.

Methods

This is a retrospective longitudinal study using the MJ health examination database in Taiwan from 2000 to 2015. There were 160,609 participants aged ≥20 years with complete obesity indicators and lung function data, and having at least two visits. A generalized estimation equation (GEE) model was applied to estimate the association between lung function and obesity.

Results

BMI was the best indicator to predict poor pulmonary function for our participants. Results of BMI are presented as an example: Obesity (body mass index (BMI) ≥27.0 kg/m²) is significantly associated with lower FVC [adjusted coefficients (β) for asthmatics: -0.11 L (95% CI: -0.14, -0.08); adjusted β for non-asthmatics: -0.08 L (-0.09, -0.08)] and FVC% [adjusted β for asthmatics: -1.91% (95% CI: -2.64, -1.19); adjusted β for non-asthmatics: 1.48% (-1.63, -1.33)]. Annual change of BMI (ΔBMI/year) is an independent risk factor for decreased FVC [adjusted β for asthmatics: -0.030 L (-0.048, -0.013); adjusted β for non-asthmatics: -0.019 L (-0.022, -0.016)] and FVC% [adjusted β for non-asthmatics: -0.603% (-1.063, -0.142); adjusted β for non-asthmatics: -0.304% (-0.393, -0.214)], and is significantly associated with accelerated FVC decline [adjusted β of ΔFVC/year and ΔFVC %/year for asthmatics: -0.038 L (-0.054, -0.022) and -0.873% (-1.312, -0.435); adjusted β of ΔFVC/year and ΔFVC %/year for non-asthmatics: -0.033 L (-0.042, -0.024) and -0.889% (-1.326, -0.452)].

Conclusion

Obesity is significantly associated with decreased lung function, and asthmatics had a higher risk than non-asthmatics.

A life course approach to elucidate the role of adiposity in asthma risk: evidence from a Mendelian randomisation study

BACKGROUND

Adiposity is associated with asthma although studies do not usually explore the inter-related role of childhood and adult adiposity in asthma risk using a life course perspective.

METHODS

We conducted a Mendelian randomisation (MR) study using genetic instruments for childhood body mass index (BMI) (n=47 541), childhood obesity (n=29 822) and adult BMI (n=681 725) applied to the UK Biobank (n=401 837), with validation in a genome-wide association study of asthma (GABRIEL, n=5616). We used inverse variance weighting and other sensitivity analyses to examine the relationship between adiposity and asthma risk. We assessed mediation using multivariable Mendelian randomisation (MVMR) analysis.

RESULTS

Childhood BMI was related to asthma in the UK Biobank (OR 1.10 per SD increase, 95% CI 0.99 to 1.22). Adult BMI was associated with asthma risk (OR 1.33 per SD increase, 95% CI 1.25 to 1.43). Analyses in GABRIEL gave directionally consistent results but with wide CI. The relationship between childhood obesity and asthma risk was less clear in both data sources. MVMR suggested the relation of childhood BMI with asthma risk was largely mediated via adult BMI.

CONCLUSION

Adiposity in childhood likely cause asthma, but the effect is primarily mediated via adult BMI.

Advances in understanding and reducing the burden of severe asthma in children

Severe asthma in children is rare, accounting for only a small proportion of childhood asthma. After addressing modifiable factors such as adherence to treatment, comorbidities, and adverse exposures, children whose disease is not well controlled on high doses of medication form a heterogeneous group of severe asthma phenotypes. Over the past decade, considerable advances have been made in understanding the pathophysiology of severe therapy-resistant asthma in children. However, asthma attacks and hospital admissions are frequent and mortality is still unacceptably high. Strategies to modify the natural history of asthma, prevent severe exacerbations, and prevent lung function decline are needed. Mechanistic studies have led to the development of several biologics targeting type 2 inflammation. This growing pipeline has the potential to reduce the burden of severe asthma; however, detailed assessment and characterisation of each child with seemingly severe asthma is necessary so that the most effective and appropriate management strategy can be implemented. Risk stratification, remote monitoring, and the integration of multiple data sources could help to tailor management for the individual child with severe asthma.

Polymorphic Inversions Underlie the Shared Genetic Susceptibility of Obesity-Related Diseases

The burden of several common diseases including obesity, diabetes, hypertension, asthma, and depression is increasing in most world populations. However, the mechanisms underlying the numerous epidemiological and genetic correlations among these disorders remain largely unknown. We investigated whether common polymorphic inversions underlie the shared genetic influence of these disorders. We performed an inversion association analysis including 21 inversions and 25 obesity-related traits on a total of 408,898 Europeans and validated the results in 67,299 independent individuals. Seven inversions were associated with multiple diseases while inversions at 8p23.1, 16p11.2, and 11q13.2 were strongly associated with the co-occurrence of obesity with other common diseases. Transcriptome analysis across numerous tissues revealed strong candidate genes for obesity-related traits. Analyses in human pancreatic islets indicated the potential mechanism of inversions in the susceptibility of diabetes by disrupting the cis-regulatory effect of SNPs from their target genes. Our data underscore the role of inversions as major genetic contributors to the joint susceptibility to common complex diseases.

Association of Healthy Lifestyle With Years Lived Without Major Chronic Diseases

Importance

It is well established that selected lifestyle factors are individually associated with lower risk of chronic diseases, but how combinations of these factors are associated with disease-free life-years is unknown.

Objective

To estimate the association between healthy lifestyle and the number of disease-free life-years.

Design, Setting, and Participants

A prospective multicohort study, including 12 European studies as part of the Individual-Participant-Data Meta-analysis in Working Populations Consortium, was performed. Participants included 116 043 people free of major noncommunicable disease at baseline from August 7, 1991, to May 31, 2006. Data analysis was conducted from May 22, 2018, to January 21, 2020.

Exposures

Four baseline lifestyle factors (smoking, body mass index, physical activity, and alcohol consumption) were each allocated a score based on risk status: optimal (2 points), intermediate (1 point), or poor (0 points) resulting in an aggregated lifestyle score ranging from 0 (worst) to 8 (best). Sixteen lifestyle profiles were constructed from combinations of these risk factors.

Main Outcomes and Measures

The number of years between ages 40 and 75 years without chronic disease, including type 2 diabetes, coronary heart disease, stroke, cancer, asthma, and chronic obstructive pulmonary disease.

Results

Of the 116 043 people included in the analysis, the mean (SD) age was 43.7 (10.1) years and 70 911 were women (61.1%). During 1.45 million person-years at risk (mean follow-up, 12.5 years; range, 4.9-18.6 years), 17 383 participants developed at least 1 chronic disease. There was a linear association between overall healthy lifestyle score and the number of disease-free years, such that a 1-point improvement in the score was associated with an increase of 0.96 (95% CI, 0.83-1.08) disease-free years in men and 0.89 (95% CI, 0.75-1.02) years in women. Comparing the best lifestyle score with the worst lifestyle score was associated with 9.9 (95% CI 6.7-13.1) additional years without chronic diseases in men and 9.4 (95% CI 5.4-13.3) additional years in women (P < .001 for dose-response). All of the 4 lifestyle profiles that were associated with the highest number of disease-free years included a body-mass index less than 25 (calculated as weight in kilograms divided by height in meters squared) and at least 2 of the following factors: never smoking, physical activity, and moderate alcohol consumption. Participants with 1 of these lifestyle profiles reached age 70.3 (95% CI, 69.9-70.8) to 71.4 (95% CI, 70.9-72.0) years disease free depending on the profile and sex.

Conclusions and Relevance

In this multicohort analysis, various healthy lifestyle profiles appeared to be associated with gains in life-years without major chronic diseases.

Association between sleep duration and asthma in different weight statuses (CHNS 2009-2015)

PURPOSE

Inadequate sleep duration affects asthma and weight. The associations among sleep duration, asthma, and different weight statuses in the Chinese population need to be further determined.

METHODS

The study included 32,776 Chinese adults from the China Health and Nutrition Survey during 2009-2015. Self-reported sleep duration was classified into three groups: ≤ 6 h (short), 7 to 8 h (optimal), and ≥ 9 h (long). Age, sex, smoking, drinking alcohol, and residence location were adjusted as potential confounding factors in a generalized estimating equations model.

RESULTS

The prevalence of asthma in the Chinese population was approximately 1.17% (383/32,776). Asthmatics were associated with shorter sleep duration and higher indices of central obesity (mean waist circumference, waist to height ratio, and conicity index) than the population without asthma. After adjusting for potential confounding factors, odds ratios (ORs) indicated positive associations between sleep duration and asthma (short vs optimal, adjusted OR = 1.74, 95%CI 1.33, 2.26; and long vs optimal, adjusted OR = 1.51, 95%CI 1.18, 1.93). When stratified by weight status, the participants with central obesity showed highest prevalence of asthma among the three sleep duration groups. With the adjustment of confounding factors, underweight and obesity grouped by waist to height ratio and conicity index remained associated with higher risk of asthma among short and long sleepers than in optimal sleepers.

CONCLUSIONS

Short and long sleepers with central obesity and underweight status were associated with significantly higher prevalence of asthma than optimal sleepers in Chinese adults.

Pediatric obesity-related asthma: A prototype of pediatric severe non-T2 asthma

Childhood obesity contributes to many diseases, including asthma. There is literature to suggest that asthma developing as a consequence of obesity has a nonallergic or non-T2 phenotype. In this review, obesity-related asthma is utilized as a prototype of non-T2 asthma in children to discuss several nonallergic mechanisms that underlie childhood asthma. Obesity-related asthma is associated with systemic T helper (Th)1 polarization occurring with monocyte activation. These immune responses are mediated by insulin resistance and dyslipidemia, metabolic abnormalities associated with obesity, that are themselves associated with pulmonary function deficits in obese asthmatics. As in other multifactorial diseases, there is both a genetic and an environmental contribution to pediatric obesity-related asthma. In addition to genetic susceptibility, differential DNA methylation is associated with non-T2 immune responses in pediatric obesity-related asthma. Initial investigations into the biology of non-T2 immune responses have identified the upregulation of genes in the CDC42 pathway. CDC42 is a RhoGTPase that plays a key role in Th cell physiology, including preferential naïve Th cell differentiation to Th1 cells, and cytokine production and exocytosis. Although these novel pathways are promising findings to direct targeted therapy development for obesity-related asthma to address the disease burden, there is evidence to suggest that dietary interventions, including diet modification, rather than caloric restriction alone, decrease disease burden. Adoption of a diet rich in micronutrients, including carotenoids and 25-OH cholecalciferol, a vitamin D metabolite, may be beneficial since these are positively correlated with pulmonary function indices, while being protective against metabolic abnormalities associated with the obese asthma phenotype.

Adiposity and asthma in adults: a bidirectional Mendelian randomisation analysis of The HUNT Study

BACKGROUND

We aimed to investigate the potential causal associations of adiposity with asthma overall, asthma by atopic status or by levels of symptom control in a large adult population and stratified by sex. We also investigated the potential for reverse causation between asthma and risk of adiposity.

METHODS

We performed a bidirectional one-sample Mendelian randomisation (MR) study using the Norwegian Nord-Trøndelag Health Study population including 56 105 adults. 73 and 47 genetic variants were included as instrumental variables for body mass index (BMI) and waist-to-hip ratio (WHR), respectively. Asthma was defined as ever asthma, doctor-diagnosed asthma and doctor-diagnosed active asthma, and was further classified by atopic status or levels of symptom control. Causal OR was calculated with the Wald method.

RESULTS

The ORs per 1 SD (4.1 kg/m²) increase in genetically determined BMI were ranged from 1.36 to 1.49 for the three asthma definitions and similar for women and men. The corresponding ORs for non-atopic asthma (range 1.42-1.72) appeared stronger than those for the atopic asthma (range 1.18-1.26), but they were similar for controlled versus partly controlled doctor-diagnosed active asthma (1.43 vs 1.44). There was no clear association between genetically predicted WHR and asthma risk or between genetically predicted asthma and the adiposity markers.

CONCLUSIONS

Our MR study provided evidence of a causal association of BMI with asthma in adults, particularly with non-atopic asthma. There was no clear evidence of a causal link between WHR and asthma or of reverse causation.