Effects of smoking on the genetic risk of obesity: the population architecture using genomics and epidemiology study

Gene polymorphisms associated with heterogeneity and senescence characteristics of sarcopenia in chronic obstructive pulmonary disease

BACKGROUND

Sarcopenia, or loss of skeletal muscle mass and decreased contractile strength, contributes to morbidity and mortality in patients with chronic obstructive pulmonary disease (COPD). The severity of sarcopenia in COPD is variable, and there are limited data to explain phenotype heterogeneity. Others have shown that COPD patients with sarcopenia have several hallmarks of cellular senescence, a potential mechanism of primary (age-related) sarcopenia. We tested if genetic contributors explain the variability in sarcopenic phenotype and accelerated senescence in COPD.

METHODS

To identify gene variants [single nucleotide polymorphisms (SNPs)] associated with sarcopenia in COPD, we performed a genome-wide association study (GWAS) of fat free mass index (FFMI) in 32 426 non-Hispanic White (NHW) UK Biobank participants with COPD. Several SNPs within the fat mass and obesity-associated (FTO) gene were associated with sarcopenia that were validated in an independent COPDGene cohort (n = 3656). Leucocyte telomere length quantified in the UK Biobank cohort was used as a marker of senescence. Experimental validation was done by genetic depletion of FTO in murine skeletal myotubes exposed to prolonged intermittent hypoxia or chronic hypoxia because hypoxia contributes to sarcopenia in COPD. Molecular biomarkers for senescence were also quantified with FTO depletion in murine myotubes.

RESULTS

Multiple SNPs located in the FTO gene were associated with sarcopenia in addition to novel SNPs both within and in proximity to the gene AC090771.2, which transcribes long non-coding RNA (lncRNA). To replicate our findings, we performed a GWAS of FFMI in NHW subjects from COPDGene. The SNP most significantly associated with FFMI was on chromosome (chr) 16, rs1558902A > T in the FTO gene (β = 0.151, SE = 0.021, P = 1.40 × 10-12 for UK Biobank |β= 0.220, SE = 0.041, P = 9.99 × 10-8 for COPDGene) and chr 18 SNP rs11664369C > T nearest to the AC090771.2 gene (β = 0.129, SE = 0.024, P = 4.64 × 10-8 for UK Biobank |β = 0.203, SE = 0.045, P = 6.38 × 10-6 for COPDGene). Lower handgrip strength, a measure of muscle strength, but not FFMI was associated with reduced telomere length in the UK Biobank. Experimentally, in vitro knockdown of FTO lowered myotube diameter and induced a senescence-associated molecular phenotype, which was worsened by prolonged intermittent hypoxia and chronic hypoxia.

CONCLUSIONS

Genetic polymorphisms of FTO and AC090771.2 were associated with sarcopenia in COPD in independent cohorts. Knockdown of FTO in murine myotubes caused a molecular phenotype consistent with senescence that was exacerbated by hypoxia, a common condition in COPD. Genetic variation may interact with hypoxia and contribute to variable severity of sarcopenia and skeletal muscle molecular senescence phenotype in COPD.

Smoking Status and Type 2 Diabetes, and Cardiovascular Disease: A Comprehensive Analysis of Shared Genetic Etiology and Causal Relationship

OBJECTIVE

This study aimed to explore shared genetic etiology and the causality between smoking status and type 2 diabetes (T2D), cardiovascular diseases (CVDs), and related metabolic traits.

METHODS

Using summary statistics from publicly available genome-wide association studies (GWASs), we estimated genetic correlations between smoking status and T2D, 6 major CVDs, and 8 related metabolic traits with linkage disequilibrium score regression (LDSC) analysis; identified shared genetic loci with large-scale genome-wide cross-trait meta-analysis; explored potential shared biological mechanisms with a series of post-GWAS analyses; and determined causality with Mendelian randomization (MR).

RESULTS

We found significant positive genetic associations with smoking status for T2D (Rg = 0.170, p = 9.39 × 10^-22), coronary artery disease (CAD) (Rg = 0.234, p = 1.96 × 10^-27), myocardial infarction (MI) (Rg = 0.226, p = 1.08 × 10^-17), and heart failure (HF) (Rg = 0.276, p = 8.43 × 10^-20). Cross-trait meta-analysis and transcriptome-wide association analysis of smoking status identified 210 loci (32 novel loci) and 354 gene-tissue pairs jointly associated with T2D, 63 loci (12 novel loci) and 37 gene-tissue pairs with CAD, 38 loci (6 novel loci) and 17 gene-tissue pairs with MI, and 28 loci (3 novel loci) and one gene-tissue pair with HF. The shared loci were enriched in the exo-/endocrine, cardiovascular, nervous, digestive, and genital systems. Furthermore, we observed that smoking status was causally related to a higher risk of T2D (β = 0.385, p = 3.31 × 10^-3), CAD (β = 0.670, p = 7.86 × 10^-11), MI (β = 0.725, p = 2.32 × 10^-9), and HF (β = 0.520, p = 1.53 × 10^-6).

CONCLUSIONS

Our findings provide strong evidence on shared genetic etiology and causal associations between smoking status and T2D, CAD, MI, and HF, underscoring the potential shared biological mechanisms underlying the link between smoking and T2D and CVDs. This work opens up a new way of more effective and timely prevention of smoking-related T2D and CVDs.

Brain-derived neurotrophic factor gene variants and obesity in former smokers

OBJECTIVE

From genome-wide association studies, brain-derived neurotrophic factor (BDNF) locus on chromosome 11 was the only SNP associated with both smoking and body mass index (BMI) in European, African and Asian population. This study aims to explore the unique genetic predisposition to obesity in former smokers by examining the effects of BDNF on BMI and waist circumference (WC).

METHODS

The study design is case-control study with a cohort validation in supplementary. We included 15,072 ethnic Chinese participants in the Guangzhou Biobank Cohort Study (GBCS) with data of four BDNF SNPs related to both BMI and smoking behavior. We used baseline smoke exposure data in 2003-2007 and follow-up outcomes of general obesity (by BMI) and central obesity (WC) in 2008-2012. Odds ratios (ORs) and 95% confidence intervals (CIs) for general obesity and central obesity associated with these SNPs were derived from logistic regression.

RESULTS

Of 15,072 participants (3169 men and 11,903 women), 1664 (11.0%) had general and 7868 (52.2%) had central obesity. In 1233 former smokers, the rs6265 GG, versus AA, genotype was associated with higher risks of general obesity (OR = 1.79, 95% CI = 1.06-3.01) and central obesity (OR = 2.08, 95% CI = 1.47-2.92) after adjustment. These associations were not significant in never or current smokers. In former heavy (≥20 cigarettes/day) smokers, the rs6265 GG genotype showed a higher odds for general obesity (OR = 2.15, 95% CI = 1.05-4.40), while no association was found in former light (1-9 cigarettes/day) smokers. Similar results were found for the association of rs6265 with central obesity and for the associations of other two BDNF SNPs (rs4923457 and rs11030104) with both general and central obesity.

CONCLUSIONS

We firstly identified the genetic predisposition (BDNF SNPs) to general and central obesity in former smokers, particularly in former heavy smokers. The different associations of the SNPs for general/central obesity in different smoke exposure groups may be related to the competitive performance of the sites and epigenetic modification, which needs further study.

Synergizing Mouse and Human Studies to Understand the Heterogeneity of Obesity

Obesity is routinely considered as a single disease state, which drives a "one-size-fits-all" approach to treatment. We recently convened the first annual University of North Carolina Interdisciplinary Nutrition Sciences Symposium to discuss the heterogeneity of obesity and the need for translational science to advance understanding of this heterogeneity. The symposium aimed to advance scientific rigor in translational studies from animal to human models with the goal of identifying underlying mechanisms and treatments. In this review, we discuss fundamental gaps in knowledge of the heterogeneity of obesity ranging from cellular to population perspectives. We also advocate approaches to overcoming limitations in the field. Examples include the use of contemporary mouse genetic reference population models such as the Collaborative Cross and Diversity Outbred mice that effectively model human genetic diversity and the use of translational models that integrate -omics and computational approaches from pre-clinical to clinical models of obesity. Finally, we suggest best scientific practices to ensure strong rigor that will allow investigators to delineate the sources of heterogeneity in the population with obesity. Collectively, we propose that it is critical to think of obesity as a heterogeneous disease with complex mechanisms and etiologies, requiring unique prevention and treatment strategies tailored to the individual.

Racial Discrimination, Racial Identity, and Obesity in Collegiate African American Women

OBJECTIVE

To investigate relationships among racial discrimination, explicit racial identity, and obesity in young collegiate African American (AA) women aged 18-25.

DESIGN

Researchers recruited 136 women who self-identified as AA from a large Midwestern university. Racial discrimination (RD) was measured using lifetime overt experiences of discrimination, recent microaggressions, and vicarious RD directed towards close others. Explicit racial identity included dimensions of private regard, public regard, and centrality. Generalized obesity (elevated body mass index) and abdominal obesity (increased fat distribution in the midsection) were measured biometrically using kg/m² and waist circumference, respectively. Hierarchical multiple regression was employed to explore main and interaction effects.

RESULTS

After controlling for adverse life events and income, overt RD, recent microaggressions, and private regard directly accounted for variance in both BMI and waist circumference. Public regard and centrality moderated relationships between RD variables and waist circumference.

CONCLUSIONS

RD and racial identity accounted for up to 13% of variance in BMI and waist circumference in main effects models among young collegiate AA women. While obesity is a multifactorial phenomenon, racial discrimination and racial identity may affect observed racial disparities in obesity rates among young women.

Breakfast consumption pattern and its association with overweight and obesity among university students: a population-based study

PURPOSE

To determine the association between breakfast consumption habit and overweight and obesity in a sample of Iranian university students.

METHODS

A sample of 78,905 university students, aged 18 years or older, was recruited from 28 provinces in Iran to assess breakfast consumption pattern. Breakfast consumption habit was evaluated using a pre-tested questionnaire. Weight and height were measured using standard protocol and then body mass index (BMI) was calculated. Overweight (obesity included) and obesity were defined as BMI ≥ 25 and BMI ≥ 30 kg/m², respectively.

RESULTS

Mean age of participants was 21.50 ± 4.01. After controlling for potential confounders, participants who ate breakfast > 4 days/week had 15% lower risk of overweight compared with those who ate < 1 day/week (OR: 0.85, 95% CI 0.78-0.92). Such significant association was also seen in female students (OR: 0.82, 95% CI 0.72-0.93); however, it was marginally significant in male ones (OR: 0.89, 95% CI 0.79-1.00). In addition, a significant inverse association was found between breakfast consumption and obesity (OR: 0.74, 95% CI 0.64-0.85) such that after adjusting for potential confounders, students who consumed breakfast > 4 days/week were 33% less likely to be obese compared with those who consumed it < 1 day/week (OR: 0.67, 95% CI 0.57-0.78). Such significant inverse association was also seen in either gender.

CONCLUSIONS

Breakfast consumption was inversely associated with odds of overweight and obesity in university students.

LEVEL OF EVIDENCE

Level V, cross-sectional descriptive studies.

Sexual Dimorphism of a Genetic Risk Score for Obesity and Related Traits among Chinese Patients with Type 2 Diabetes

BACKGROUND

Obesity is more prevalent in men than in women in China, especially within the middle-aged population.

OBJECTIVES

The present study aims to determine the contribution of sexual dimorphisms to obesity and related traits in terms of the mechanisms involving the obesity-related genetic variants among patients of Chinese Han ancestry with type 2 diabetes.

METHOD

In the Chinese National Diabetes and Metabolic Disorders Study, 2,555 out of 4,036 patients with type 2 diabetes were treatment naive, including 1,142 men and 1,413 women. Single-nucleotide polymorphisms (SNP) from 18 genomic loci previously found to be associated with obesity-related traits were successfully genotyped, and a genetic risk score (GRS) was constructed by summing the risk alleles for obesity.

RESULTS

Single SNP analysis showed that genetic variants in SLC30A10, TMEM18, GNPDA2, PRL, TFAP2B, BDNF, MTCH2, FTO, and MC4R were nominally associated with waist circumference (WC), BMI, and risk for abdominal or general obesity in the untreated patients with type 2 diabetes, as well as in the total group of patients with type 2 diabetes (untreated and treated) (p < 0.05). Interactions between sex and SNP in PRL, MTCH2,and FTO were detected (p < 0.05). In the untreated patients with diabetes, the GRS was nominally associated with WC (β = 0.0032, SE = 0.0011; p = 0.003), BMI (β = 0.0030, SE = 0.0013; p = 0.027), and increased risk for abdominal (OR = 1.08; 95% CI 1.02-1.13; p = 0.004) or general obesity (OR = 1.07; 95% CI 1.02-1.13; p = 0.011) in men but not in women. GRS-sex interactions were detected in the determinant of WC (p = 0.019) and abdominal obesity (p = 0.016). Among patients aged 30-60 years, GRS was found to be significantly associated with WC (β = 0.0050, SE = 0.0016; p = 0.002) and abdominal obesity (OR = 1.10; 95% CI 1.04-1.17; p = 0.001) and nominally associated with BMI (β = 0.0057, SE = 0.0020; p = 0.005) and general obesity (OR = 1.07; 95% CI 1.01-1.14; p = 0.027) in men, whereas in women none of the associations were detected. GRS-sex interactions were present in the determinant of WC (p = 0.015), BMI (p = 0.032), and abdominal obesity (p = 0.012). Among patients aged 60 years or older, neither an association of GRS with obesity-related traits nor GRS-sex interactions were detected.

CONCLUSIONS

Genetic factors contribute to obesity-related traits in a sex-dependent pattern among middle-aged Chinese, and men tend to be more susceptible to the genetic risk of obesity.

Smoking modifies the effect of two independent SNPs rs5063 and rs198358 of NPPA on central obesity in the Chinese Han population

Obesity is the third most risk factors of death in the middle-income and high-income countries. Whether DNA polymorphisms in CORIN and NPPA genes were associated with obesity, and if these associations could be modified by smoking in the Chinese Han population were unknown, hence a group of 1507 participants were recruited and genotyped for 12 tag single-nucleotide polymorphisms (SNPs) of CORIN and NPPA genes. Regression models were used to test the associations of SNPs with obesity. The potential SNP-smoking interactions were detected in regression models. NPPA SNPs rs5063 and rs198358 were associated with the body mass index (BMI) (P = 0.0053 and 0.0037, respectively). Rs198358 was associated with obesity in both univariate- and multivariable-adjusted analyses (P = 0.0138 and 0.0173, respectively). Rs5063 was associated with central obesity in both univariate- and multivariable-adjusted analyses (P = 0.0454 and 0.0361, respectively). Significant interactions between cigarette smoking and rs5063 and rs198358 were detected (P = 0.0019 and 0.0006, respectively). In subgroup analyses, rs5063 and rs198358 were associated with central obesity in smokers (P = 0.0081 and 0.0037, respectively). The results of our study demonstrated that the effect of NPPA SNPs rs5063 and rs198358 on central obesity might be modified by smoking in the Chinese Han population. Further studies are needed to confirm the associations and elucidate the underlying mechanisms.

A hierarchical Bayesian tri-variate analysis on factors associated with anthropometric measures in a large sample of children and adolescents: the CASPIAN-IV study

BACKGROUND

This study aimed to assess determinants of anthropometric measures in a nationally representative sample of Iranian children and adolescents.

METHODS

This nationwide study was conducted among 13,280 students, aged 6-18 years, who were randomly selected from 30 provinces in Iran. Anthropometric measures were determined by calibrated instruments. Demographic and socio-economic (SES) variables, lifestyle behaviors, family history of chronic disease and prenatal factors were studied, as well. A hierarchical Bayesian tri-variate analysis was used to assess the factors associated with obesity measures of the body mass index (BMI), waist-to-height ratio (WHtR) and wrist circumference (WrC).

RESULTS

The results showed that the BMI was associated with SES score, family history of obesity, family history of diabetes mellitus, physical inactivity, screen time, duration of sleep, breakfast consumption, birth weight, breastfeeding, junk food and place of residence (urban-rural). All these factors were also significantly associated with WrC except for consumption of junk food. Many of these factors had a partial but significant relationship with WHtR.

CONCLUSIONS

Various factors contribute to obesity. Preventive and educational programs on manageable factors such as increasing physical activity, eating breakfast and limiting TV or screen time could be helpful in controlling obesity in schoolchildren and reducing associated complications.

Complex Relationship between Obesity and the Fat Mass and Obesity Locus

In the 21st century, obesity has become a serious problem because of increasing obese patients and numerous metabolic complications. The primary reasons for this situation are environmental and genetic factors. In 2007, FTO (fat mass and obesity associated) was the first gene identified through a genome-wide association study (GWAS) associated with obesity in humans. Subsequently, a cluster of single nucleotide polymorphisms (SNPs) in the first intron of the FTO gene was discovered to be associated with BMI and body composition. Various studies have explored the mechanistic basis behind this association. Thus, emerging evidence showed that FTO plays a key role regulating adipose tissue development and functions in body size and composition. Recent prevalent research topic concentrated in the three neighboring genes of FTO: RPGRIP1L, IRX3 and IRX5, as having a functional link between obesity-associated common variants within FTO and the observed human phenotypes. The purpose of this review is to present a comprehensive picture of the impact of FTO on obesity susceptibility and to illuminate these new studies of FTO function in adipose tissue.

Assessing gene-environment interaction effects of FTO, MC4R and lifestyle factors on obesity using an extreme phenotype sampling design: Results from the HUNT study

BACKGROUND

Our aim was to assess the influence of age, gender and lifestyle factors on the effect of the obesity-promoting alleles of FTO and MCR4.

METHODS

The HUNT study comprises health information on the population of Nord-Trøndelag county, Norway. Extreme phenotype participants (gender-wise lower and upper quartiles of waist-hip-ratio and BMI ≥ 35 kg/m2) in the third survey, HUNT3 (2006-08), were genotyped for the single-nucleotide polymorphisms rs9939609 (FTO) and rs17782313 (MC4R); 25686 participants were successfully genotyped. Extreme sampling was chosen to increase power to detect genetic and gene-environment effects on waist-hip-ratio and BMI. Statistical inference was based on linear regression models and a missing-covariate likelihood approach for the extreme phenotype sampling design. Environmental factors were physical activity, diet (artificially sweetened beverages) and smoking. Longitudinal analysis was performed using material from HUNT2 (1995-97).

RESULTS

Cross-sectional and longitudinal genetic effects indicated stronger genetic associations with obesity in young than in old, as well as differences between women and men. We observed larger genetic effects among physically inactive compared to active individuals. This interaction was age-dependent and seen mainly in 20-40 year olds. We observed a greater FTO effect among men with a regular intake of artificially sweetened beverages, compared to non-drinkers. Interaction analysis of smoking was mainly inconclusive.

CONCLUSIONS

In a large all-adult and area-based population survey the effects of obesity-promoting minor-alleles of FTO and MCR4, and interactions with life style factors are age- and gender-related. These findings appear relevant when designing individualized treatment for and prophylaxis against obesity.

The association of cigarette smoking and alcohol drinking with body mass index: a cross-sectional, population-based study among Chinese adult male twins

Background

Obesity is a multifactorial abnormality which has an underlying genetic control but requires environmental influences to trigger. Numerous epidemiological studies have examined the roles of physical inactivity and dietary factors in obesity development. Interactions between obesity-related genes and these lifestyles have also been confirmed. However, less attention has been paid to these complex relationship between cigarette smoking, alcohol drinking and obesity. The purpose of this study was to assess whether cigarette smoking and alcohol drinking were associated with body mass index (BMI), and whether these lifestyle factors modified the genetic variance of BMI.

Methods

Subjects were twins recruited through the Chinese National Twin Registry, aged 18 to 79 years, and the sample comprised 6121 complete male twin pairs. Information on height, weight, cigarette smoking and alcohol drinking status were assessed with self-report questionnaires. The associations of cigarette smoking and alcohol drinking with BMI were evaluated by linear regression models. Further, structure equation models were conducted to estimate whether cigarette smoking and alcohol drinking status modified the degree of genetic variance of BMI.

Results

After adjustment for a variety of socio-demographic and lifestyle factors, former smokers had higher BMI (β = 0.475; 95 % CI, 0.196 to 0.754) whereas moderate to heavy smokers had lower BMI (β = −0.115; 95 % CI, −0.223 to −0.007) when compared with nonsmokers. BMI decreased with increased cigarette pack-years (β = −0.008; 95 % CI, −0.013 to −0.003). These effects still existed substantially in within-MZ twin pair analyses. By contrast, current alcohol drinking had no significant influence on BMI when additionally controlled for shared factors in within-pair analyses. Genetic modification by alcohol drinking was statistically significant for BMI (β = −0.137; 95 % CI, −0.215 to −0.058), with the intake of alcohol decreasing the additive genetic component of BMI.

Conclusions

Cigarette smoking was negatively associated with BMI independent of genetic influences. The influence of genes on BMI was moderated by alcohol drinking, such that for individuals who were regular drinkers, genetic factors became less influential. Our findings highlight gene-alcohol interaction in finding candidate genes of BMI and elucidating the etiological factors of obesity.

Interaction of smoking and obesity susceptibility loci on adolescent BMI: The National Longitudinal Study of Adolescent to Adult Health

BACKGROUND

Adolescence is a sensitive period for weight gain and risky health behaviors, such as smoking. Genome-wide association studies (GWAS) have identified loci contributing to adult body mass index (BMI). Evidence suggests that many of these loci have a larger influence on adolescent BMI. However, few studies have examined interactions between smoking and obesity susceptibility loci on BMI. This study investigates the interaction of current smoking and established BMI SNPs on adolescent BMI. Using data from the National Longitudinal Study of Adolescent to Adult Health, a nationally-representative, prospective cohort of the US school-based population in grades 7 to 12 (12-20 years of age) in 1994-95 who have been followed into adulthood (Wave II 1996; ages 12-21, Wave III; ages 18-27), we assessed (in 2014) interactions of 40 BMI-related SNPs and smoking status with percent of the CDC/NCHS 2000 median BMI (%MBMI) in European Americans (n = 5075), African Americans (n = 1744) and Hispanic Americans (n = 1294).

RESULTS

Two SNPs showed nominal significance for interaction (p < 0.05) between smoking and genotype with %MBMI in European Americans (EA) (rs2112347 (POC5): β = 1.98 (0.06, 3.90), p = 0.04 and near rs571312 (MC4R): β 2.15 (-0.03, 4.33) p = 0.05); and one SNP showed a significant interaction effect after stringent correction for multiple testing in Hispanic Americans (HA) (rs1514175 (TNNI3K): β 8.46 (4.32, 12.60), p = 5.9E-05). Stratifying by sex, these interactions suggest a stronger effect in female smokers.

CONCLUSIONS

Our study highlights potentially important sex differences in obesity risk by smoking status in adolescents, with those who may be most likely to initiate smoking (i.e., adolescent females), being at greatest risk for exacerbating genetic obesity susceptibility.

Interactions of smoking with rs833061 polymorphism on the risk of non-alcoholic fat liver disease in Hubei Han population: a preliminary case-control study

OBJECTIVES

Vascular endothelial growth factor (VEGF) has biological actions on energy homeostasis, inflammation and insulin resistance. The present study aimed to investigate the association between VEGF -460 T/C (rs833061), and +936 C/T (rs3025039) polymorphism and risk of non-alcohol fatty liver disease (NAFLD) in Hubei Han population and to further explore the interactions of smoking with rs833061 and rs3025039.

MATERIALS AND METHODS

341 healthy controls and 246 cases were recruited. Two variants, rs833061 and rs3025039, were genotyped by polymerase chain reaction (PCR)-restriction fragment length polymorphism (RFLP). The unconditional logistic regression (ULR) was performed to assess the association of the two variants with risk of NAFLD. Gene-environment interactions on the risk of NAFLD were preliminarily explored by generalized multifactor dimensionality reduction (GMDR) and further confirmed by ULR methods.

RESULTS

After adjusting for covariates, increased risk of NAFLD was observed in patients carrying CT/CC genotypes in rs833061 and rs3025039 (ORa=1.80, 95% confidence interval (CI): 1.51, 2.36, Pa =0.000; ORa=1.89, 95% CI: 1.41, 2.82, Pa =0.000, respectively). Interaction of smoking with rs833061 was found by GMDR, with maximum prediction accuracy (67.91%) and a maximum cross-validation consistency (10/10). ULR method confirmed that, smoking-positive patients with genotype CT/CC had 4.93 times risk of NAFLD compared to smoking-negative participants with genotype TT (ORadd (a)=4.93, 95% CI: 2.91, 8.54, P add (a)=0.000), which further confirmed synergistic effects.

CONCLUSION

The results indicated that both rs833061 and rs3025039 are associated with NAFLD risk. Furthermore, rs833061 is likely to have an interaction with smoking, and they have synergistic effects on risk of NAFLD in Hubei Han population.

Age plays an important role in the relationship between smoking status and obesity risk: a large scale cross-sectional study of Chinese adults

OBJECTIVE

To study the role of age plays in the relationship between smoking status and obesity in both Chinese men and women.

METHODS

From Chinese Physical and Psychological Database, participants were divided into non-smokers, current smokers, and former smokers. Body mass index (BMI), waist circumference (WC), fat percentage, fat mass, and fat free mass were measured. The mean, standard deviation and frequency of these indicators were calculated for each age bracket. One-way ANOVA and post-hoc test analyses were used to detect the difference among these three groups.

RESULTS

In men, from 19 to 24 years old, BMI, WC and fat free mass of current smokers were higher than that of non-smokers (P<0.01). However, fat mass and fat percentage of current smokers were lower than that of non-smokers but higher than that of former smokers (P<0.01). From 25 to 34 years old, BMI and fat mass of former smokers were higher than non-smokers and current smokers (P<0.01). In addition, WC and fat free mass of non-smokers were lower than that of current smokers and former smokers (P<0.01). From 45 to older, BMI, WC, fat mass, fat free mass and fat percentage of former smokers were higher than that of current smokers (P<0.01). From 55 to older, BMI, WC, fat mass, fat free mass and fat percentage of current smokers were lower than that of non-smokers (P<0.01). In women, smoking status might not be significantly related to obesity (P>0.05).

CONCLUSION

For young men, smoking might have an effect on increasing fat free mass, BMI and WC, and decreasing fat mass and fat percentage. For middle and older men, smoking might have an effect on decreasing fat free mass, fat mass, BMI, WC, and fat percentage. Obesity risk should be paid more attention in smoking cessation programs for those former smokers.

First genome-wide association study in an Australian aboriginal population provides insights into genetic risk factors for body mass index and type 2 diabetes

A body mass index (BMI) >22kg/m² is a risk factor for type 2 diabetes (T2D) in Aboriginal Australians. To identify loci associated with BMI and T2D we undertook a genome-wide association study using 1,075,436 quality-controlled single nucleotide polymorphisms (SNPs) genotyped (Illumina 2.5M Duo Beadchip) in 402 individuals in extended pedigrees from a Western Australian Aboriginal community. Imputation using the thousand genomes (1000G) reference panel extended the analysis to 6,724,284 post quality-control autosomal SNPs. No associations achieved genome-wide significance, commonly accepted as P<5x10^-8. Nevertheless, genes/pathways in common with other ethnicities were identified despite the arrival of Aboriginal people in Australia >45,000 years ago. The top hit (rs10868204 P_genotyped = 1.50x10^-6; rs11140653 P_{imputed_1000G} = 2.90x10^-7) for BMI lies 5’ of NTRK2, the type 2 neurotrophic tyrosine kinase receptor for brain-derived neurotrophic factor (BDNF) that regulates energy balance downstream of melanocortin-4 receptor (MC4R). PIK3C2G (rs12816270 P_genotyped = 8.06x10^-6; rs10841048 P_{imputed_1000G} = 6.28x10^-7) was associated with BMI, but not with T2D as reported elsewhere. BMI also associated with CNTNAP2 (rs6960319 P_genotyped = 4.65x10^-5; rs13225016 P_{imputed_1000G} = 6.57x10^-5), previously identified as the strongest gene-by-environment interaction for BMI in African-Americans. The top hit (rs11240074 P_genotyped = 5.59x10^-6, P_{imputed_1000G} = 5.73x10^-6) for T2D lies 5’ of BCL9 that, along with TCF7L2, promotes beta-catenin’s transcriptional activity in the WNT signaling pathway. Additional hits occurred in genes affecting pancreatic (KCNJ6, KCNA1) and/or GABA (GABRR1, KCNA1) functions. Notable associations observed for genes previously identified at genome-wide significance in other populations included MC4R (P_genotyped = 4.49x10^-4) for BMI and IGF2BP2 P_{imputed_1000G} = 2.55x10^-6) for T2D. Our results may provide novel functional leads in understanding disease pathogenesis in this Australian Aboriginal population.

Modification of genetic influences on adiposity between 36 and 63 years of age by physical activity and smoking in the 1946 British Birth Cohort Study

Background:

Previous studies reporting on the interaction between physical activity and genetic susceptibility on obesity have been cross-sectional and have not considered the potential influences of other lifestyle behaviours. The aim of this study was to examine modification of genetic influences on changes across age in adiposity during mid-adulthood by physical activity and smoking.

Methods:

The sample comprised 2444 participants who were genotyped for 11 obesity variants and had body mass index (BMI), waist circumference-to-height ratio (WHtR), physical activity and smoking measures at 36, 43, 53 and 60–64 years of age. A genetic risk score (GRS) comprising the sum of risk alleles was computed. Structural equation models investigated modification of the longitudinal GRS associations by physical activity (active versus inactive) and smoking (non-smoker versus smoker), using a latent linear spline to summarise BMI or WHtR (multiplied by 100) at the age of 36 years and their subsequent rates of change over age.

Results:

Physical activity at the age of 36 years attenuated the GRS associations with BMI and WHtR at the same age (P-interaction 0.009 and 0.004, respectively). Further, physical activity at the age of 53 years attenuated the GRS association with rate of change in BMI between 53 and 63 years of age (by 0.012 kg m⁻² per year (95% confidence interval (CI): 0.001, 0.024), P-interaction 0.004). Conversely, smoking at the age of 43 years showed a trend towards augmenting the GRS association with rate of change in WHtR between 43 and 63 years of age (by 0.012 (95% CI: 0.001, 0.026), P-interaction 0.07). Estimated GRS effect sizes were lowest at all ages in the healthiest group (e.g., active non-smokers).

Conclusions:

Healthy lifestyle behaviours appeared to attenuate the genetic influence on changes across age in BMI and central adiposity during mid-adulthood. An active lifestyle and not smoking may have additive effects on reducing the genetic susceptibility to obesity in adults.

The bigger picture of FTO: the first GWAS-identified obesity gene

Single nucleotide polymorphisms (SNPs) that cluster in the first intron of fat mass and obesity associated (FTO) gene are associated obesity traits in genome-wide association studies. The minor allele increases BMI by 0.39 kg/m(2) (or 1,130 g in body weight) and risk of obesity by 1.20-fold. This association has been confirmed across age groups and populations of diverse ancestry; the largest effect is seen in young adulthood. The effect of FTO SNPs on obesity traits in populations of African and Asian ancestry is similar or somewhat smaller than in European ancestry populations. However, the BMI-increasing allele in FTO is substantially less prevalent in populations with non-European ancestry. FTO SNPs do not influence physical activity levels; yet, in physically active individuals, FTO's effect on obesity susceptibility is attenuated by approximately 30%. Evidence from epidemiological and functional studies suggests that FTO confers an increased risk of obesity by subtly changing food intake and preference. Moreover, emerging data suggest a role for FTO in nutrient sensing, regulation of mRNA translation and general growth. In this Review, we discuss the genetic epidemiology of FTO and discuss how its complex biology might link to the regulation of body weight.