title: The association of cigarette smoking and alcohol drinking with body mass index: a cross-sectional, population-based study among Chinese adult male twins.
abstract: 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.
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, 100191, China.
authors.forename: Chunxiao
authors.initials: C
authors.lastname: Liao
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, 100191, China. gaowenjing1979@gmail.com.
authors.forename: Wenjing
authors.initials: W
authors.lastname: Gao
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, 100191, China.
authors.forename: Weihua
authors.initials: W
authors.lastname: Cao
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, 100191, China.
authors.forename: Jun
authors.initials: J
authors.lastname: Lv
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, 100191, China.
authors.forename: Canqing
authors.initials: C
authors.lastname: Yu
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, 100191, China.
authors.forename: Shengfeng
authors.initials: S
authors.lastname: Wang
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, 100191, China.
authors.forename: Bin
authors.initials: B
authors.lastname: Zhou
authors.affiliation: Qingdao Center for Diseases Control and Prevention, Qingdao, 266033, China.
authors.forename: Zengchang
authors.initials: Z
authors.lastname: Pang
authors.affiliation: Zhejiang Center for Disease Control and Prevention, Hangzhou, 310051, China.
authors.forename: Liming
authors.initials: L
authors.lastname: Cong
authors.affiliation: Beijing Center for Disease Control and Prevention, Beijing, 100013, China.
authors.forename: Zhong
authors.initials: Z
authors.lastname: Dong
authors.affiliation: Shanghai Center for Disease Control and Prevention, Shanghai, 200336, China.
authors.forename: Fan
authors.initials: F
authors.lastname: Wu
authors.affiliation: Jiangsu Center for Disease Control and Prevention, Nanjing, 210009, China.
authors.forename: Hua
authors.initials: H
authors.lastname: Wang
authors.affiliation: Sichuan Center for Disease Control and Prevention, Chengdu, 610041, China.
authors.forename: Xianping
authors.initials: X
authors.lastname: Wu
authors.affiliation: Tianjin Center for Disease Control and Prevention, Tianjin, 300011, China.
authors.forename: Guohong
authors.initials: G
authors.lastname: Jiang
authors.affiliation: Qinghai Center for Disease Control and Prevention, Xining, 810007, China.
authors.forename: Xiaojie
authors.initials: X
authors.lastname: Wang
authors.affiliation: Harbin Medical University, Harbin, 150081, China.
authors.forename: Binyou
authors.initials: B
authors.lastname: Wang
authors.affiliation: Department of Epidemiology and Biostatistics, School of Public Health, Peking University, Beijing, 100191, China. lmlee@vip.163.com.
authors.forename: Liming
authors.initials: L
authors.lastname: Li
mesh_terms: D000293:Adolescent; D000328:Adult; D000368:Aged; D000428:Alcohol Drinking / Q000453:epidemiology* / Q000235:genetics; D015992:Body Mass Index; D002681:China / Q000453:epidemiology; D003430:Cross-Sectional Studies; D006801:Humans; D008019:Life Style; D008297:Male; D008875:Middle Aged; D009765:Obesity / Q000453:epidemiology* / Q000235:genetics; D012042:Registries; D012307:Risk Factors; D012907:Smoking / Q000453:epidemiology* / Q000235:genetics; D011795:Surveys and Questionnaires; D014427:Twins / Q000706:statistics & numerical data; D055815:Young Adult
keywords: Alcohol drinking; Body mass index; Gene-environment interaction; Smoking; Twin studies