Risk factors associated with body mass index increase in men at 28 years follow-up.

Background: Several studies have reported a general increase in body mass index (BMI).

Aim: To identify factors influencing BMI changes at 28 years follow-up.

Design: Prospective screening study.

Methods: The cohort of the Oslo I study of 1972/73 had another screening in 2000 (Oslo II). We present data for these men, and men from Oslo I who participated in five similar studies during 1996-2001. In all, 7157 men aged 20-49 years at first screening attended two health screenings, and complete data were available for 7104. BMI change from 1972/73 to 2000 was the dependent variable in multiple regression analyses.

Results: The percentage with obesity (BMI > or = 30) increased overall from 2.5% to 13.5%. The overall mean (SD) BMI increased from 24.2 (2.6) kg/m2 to 26.2 (3.4) kg/m2. The increase was largest (3.9 (2.5) kg/m2) among men aged 20-24 in 1972/73 and least (1.6 (2.5) kg/m2) in those aged 45-49 years. No age trend was observed for those with BMI > or = 30.0 kg/m2 in 1972/3. On multiple regression analysis, increasing triglycerides, systolic blood pressure, age and non-fasting glucose, decreasing physical activity and not smoking were all significantly related to increasing BMI. Having stopped smoking was also related to increased BMI. Daily smoking in both 1972/73 and 2000, and daily smoking in 2000 but not in 1972/73, were inversely related to increased BMI.

Discussion: There was a substantial increase in BMI, with the largest increase in the younger men, except in those who were already obese at first screening. Overall, obesity increased by 11% in the study period and was associated with multiple life-style factors.