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Gene x environment interaction of vigorous exercise and body mass index among male Vietnam-era twins

¹ From the Weight Control and Diabetes Research Center, Brown Medical School and The Miriam Hospital, Providence, RI (JMM, DSB, and RRW); the Center for Statistical Sciences, Brown Medical School, Providence, RI (GDP); the Department of Psychology, Boston University, Boston, MA (MJL); the Harvard Institute of Psychiatric Epidemiology and Genetics, the Departments of Epidemiology and Psychiatry, Boston, MA (MJL); and the Harvard Medical School, Department of Psychiatry at the Massachusetts Mental Health Center, Boston, MA (MJL).

² Supported by NIH grant HL-72819 (to JMM).

³ Reprints not available. Address correspondence to JM McCaffery, Weight Control and Diabetes Research Center, 196 Richmond Street, Providence, RI 02903. E-mail: jeanne_mccaffery{at}brown.edu.

Background: Secular trends over the past several decades suggest an environmental influence on body mass index (BMI). However, twin models that incorporate a gene-environment correlation and gene x environment interaction have not been applied to elucidate specific environmental factors that affect the heritability of BMI.

Objective: Our aim was to determine whether one putative environmental predictor of obesity, vigorous exercise, shows evidence of a gene-environment correlation or gene x environment interaction with BMI among twins.

Design: Twin structural equation modeling was used to examine a gene-environment correlation and a gene x environment interaction of vigorous exercise with BMI among 2710 monozygotic and 2327 dizygotic male-male twin pairs from the Vietnam Era Twin Registry—a national registry of twin pairs who served in the military during the Vietnam War era.

Results: Vigorous exercise significantly modified the additive genetic component of BMI, which indicated a gene x environment interaction (P < 0.001). BMI showed the greatest genetic influence among those who did not report vigorous exercise, with diminished genetic influence among those who did. Furthermore, vigorous exercise had a small but significant environmental effect on BMI (P = 0.006)—a finding confirmed among monozygotic co-twins discordant for vigorous exercise.

Conclusions: Genetic influences on BMI are lower among those who report vigorous exercise. Consistent with an emerging literature, this suggests that vigorous exercise may mitigate some of the genetic influence on obesity. Molecular genetic studies of obesity should consider incorporating measures of behavioral and demographic factors to maximize the identification of novel obesity genes.

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