Abstract
Background and objectivesThere is no doubt that the dramatic worldwide increase in obesity prevalence is due to changes in environmental factors. However, twin studies suggest that genetic differences are responsible for the major part of the variation in body mass index (BMI) and other measures of body fatness within populations. Several recent studies suggest that the genetic effects on adiposity may be stronger when combined with presumed risk factors for obesity. We tested the hypothesis that a higher prevalence of obesity and overweight and a higher BMI mean is associated with a larger genetic variation in BMI.MethodsThe data consisted of self-reported height and weight from two Danish twin surveys in 1994 and 2002. A total of 15,017 monozygotic and dizygotic twin pairs were divided into subgroups by year of birth (from 1931 through 1982) and sex. The genetic and environmental variance components of BMI were calculated for each subgroup using the classical twin design. Likewise, the prevalence of obesity, prevalence of overweight and the mean of the BMI distribution was calculated for each subgroup and tested as explanatory variables in a random effects meta-regression model with the square root of the additive genetic variance (equal to the standard deviation) as the dependent variable.ResultsThe size of additive genetic variation was positively and significantly associated with obesity prevalence (p = 0.001) and the mean of the BMI distribution (p = 0.015). The association with prevalence of overweight was positive but not statistically significant (p = 0.177).ConclusionThe results suggest that the genetic variation in BMI increases as the prevalence of obesity, prevalence of overweight and the BMI mean increases. The findings suggest that the genes related to body fatness are expressed more aggressively under the influence of an obesity-promoting environment.
Highlights
The prevalence of obesity has increased at epidemic rates in most parts of the world in the last decades, and in the USA recent data show that more than a third of all men and women are obese [1,2]
The results suggest that the genetic variation in body mass index (BMI) increases as the prevalence of obesity, prevalence of overweight and the BMI mean increases
The findings suggest that the genes related to body fatness are expressed more aggressively under the influence of an obesity-promoting environment
Summary
The prevalence of obesity has increased at epidemic rates in most parts of the world in the last decades, and in the USA recent data show that more than a third of all men and women are obese [1,2]. It has been suggested that part of the discrepancy between heritability and the genetic variation from currently identified genes could be attributable to interaction effects between genetic loci, i.e. epistatic effects, or interaction between genes and the environment The latter implies that the effect of genes depend upon the environmental exposure and vice versa. Fat and carbohydrate intake has been found to interact with the FTO gene on BMI [15] These results all suggest that genetic effects on adiposity are modifiable by environmental influences. The research is still at an early stage and it is possible that the discovered interactions apply to other genetic loci and environmental factors than physical activity, fat and carbohydrate intake On this background we tested the more general hypothesis that the genetic variance component of BMI is higher in populations with a higher prevalence of obesity, a higher prevalence of overweight and a higher mean BMI.
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