Age, period and cohort effects on body weight and body mass index in adults: The Doetinchem Cohort Study

To study the development of body weight with ageing, in a general adult population, taking into account possible period and cohort effects. A prospective cohort study with 11 years of follow-up. At baseline and after 6 and 11 years, body weight and height were measured. The Doetinchem Cohort Study, consisting of inhabitants of Doetinchem, a town in a rural area of The Netherlands. In total, 4070 healthy men and women aged 20-59 years at baseline. Increase in BMI with ageing was less profound based on cross-sectional data than based on longitudinal data. More recent-born cohorts had a higher BMI at a given age than cohorts who were born earlier. Increase in mean BMI with ageing was observed in all age groups and was similar for groups with a different educational level. Highest increase in BMI over 11 years was observed in the youngest group, aged 20-29 years at baseline (2.2 [95 % CL 2.0, 2.3] kg/m2), and lowest increase in the oldest group, aged 50-59 years at baseline (1.1 [1.0, 1.3] kg/m2). Findings of the present study using longitudinal data suggest that increase in BMI with ageing is underestimated in all age groups by studying cross-sectional data only. Further, weight gain is present in all educational levels and does not stop at middle age.