Secular trends in body mass index by birth cohort in eastern Finland from 1972 to 1997

OBJECTIVE: To describe changes in body mass index (BMI) with age over a 25 y period, and to investigate whether those changes differed by birth cohort , gender or education. DESIGN: Six cross-sectional population surveys repeated in eastern Finland every fifth year between 1972 and 1997. Synthetic birth cohorts were create d by dividing subjects into twelve 5 y groups according to birth year. SUBJECTS: Independent random samples from the national population register including men and women aged 25 - 64 y, the final sample comprising 18 439 men and 19 501 women. The oldest birth cohort included subjects born in 191 3 - 1917 and the youngest were born in 1968 - 1972. MEASUREMENTS: Weight and height were measured, and data on educational leve l were collected by a self-administered questionnaire. RESULTS: A BMI increase with age was more prominent in women (4.2 kg/m(2) i n 25 y) than in men (3.3 kg/m(2) in 25 y), and was very similar in all birt h cohorts. In men, the BMI increase with age varied across cohorts. Among b irth cohorts participating in each survey, the BMI increase over the 25 y p eriod was most prominent (3.9 kg/m(2) in 25 y) in men born between 1943 and 1947. Among all birth cohorts, the strongest upward trend (0.2 kg/m(2) per year) was observed in men born between 1953 and 1957. CONCLUSIONS: Weight gain with age has remained unchanged in women over the 25 y period, whereas in men, the younger the birth cohort, the more promine nt was the BMI increase with age.