Variation in the heritability of body mass index based on diverse twin studies: a systematic review

Summary Objectives Over the past three decades, twin studies have shown variation in the heritability of obesity. This study examined the difference of body mass index ( BMI ) heritability ( BMI ‐ H ) by population characteristics, such as sex, age, time period of observation and average BMI , as well as by broad social‐environmental factors as indicated by country‐level gross domestic product ( GDP ) per capita and GDP growth rate. Methods Twin studies that reported BMI ‐ H and were published in E nglish from J anuary 1990 to F ebruary 2011 after excluding those with disease, special occupations or combined heritability estimates for country/ethnic groups were searched in P ub M ed. 32 studies were identified from F inland (7), the U nited K ingdom (6), the U nited S tates (3), D enmark (3), C hina (3), N etherlands (2), S outh K orea (2), S weden (2) and four from other countries. Meta‐regression models with random effects were used to assess variation in BMI ‐ H . Results Heterogeneity of BMI ‐ H is significantly attributable to variations in age (<20, 20–55 and ≥56 years), time period of observation (i.e. year of data collection), average BMI and GDP (≤$20,000, $20,001–26,000 and >$26,000). BMI ‐ H was higher in adolescents (<20 years), in studies done in past years, and in populations with higher average BMI s or higher GDP per capita (≥$26,000) than their counterparts. Consistent lowering effects of high GDP growth rate (>median) on BMI ‐ H were shown through stratified analyses by GDP . BMI ‐ H was lower in countries of mid‐level GDP , particularly those experiencing rapid economic growth. Conclusions BMI ‐ H is sensitive to age, time period of observation, average BMI , GDP and rapid economic growth.