Genetic and environmental effects on weight gain from young adulthood to old age and its association with body mass index in early young adulthood: an individual-based pooled analysis of 16 twin cohorts.

introductionGenetic and environmental factors contribute to weight gain, but how these effects change over adulthood is largely unknown. We examined how genetic factors influence BMI changes from young adulthood to old age and how this change relates to BMI in early adulthood. DATA AND

methodsData from 16 longitudinal twin cohorts, including 111,370 adults (56% women) and 55,657 complete twin pairs (42% monozygotic), were pooled. The data were divided into three stages (young adulthood-early middle age, late middle age, and old age). BMI changes were calculated via linear mixed effects and delta slope methods. Genetic and environmental contributions to these changes and their correlations with BMI in early young adulthood were estimated through structural equation modeling.

resultsThe average BMI increase per year was 0.18 kg/m² in men and 0.15 kg/m² in women during young adulthood-early middle age (18-50 years), decreasing to ≤0.07 kg/m² at older ages. Genetic effects contributed to variance of BMI changes during young adulthood-early middle age (men a² = 0.29; women a² = 0.26) and less so in late middle age (51-64 years) (men a² = 0.05; women a² = 0.16) and old age ( > 65 years) (men a² = 0.13; women a² = 0.18). Most variation was explained by non-shared environmental effects (e² = 0.71-0.95 in men and e²= 0.74-0.84 in women). In men, greater BMI during early young adulthood (18-30 years) was associated with lower BMI changes later in life (r = -0.22 to -0.13), and the association was driven by genetic (r

conclusionGenotype influences BMI changes across adulthood, with its effect varying by age and sex. Environmental effects are the main drivers of adult BMI changes, highlighting the role of modifiable factors in long-term weight regulation.