Background: Obesity is a risk factor for a number of chronic diseases. Few longitudinal studies have examined changes in body mass index (BMI [calculated as weight in kilograms divided by the square of the height in meters]).
Objective: To investigate the changes in mean BMI and the prevalence of obesity in a large cohort examined several times during a 20-year period.
Methods: Mean BMI, the percentage of subjects with low BMI (<20 kg/m(2)), and the percentage who were obese (BMI > or =30 kg/m(2)) were determined in a large population of men and women who were examined up to 4 times during a 20-year period (1974-1994/1995). In a longitudinal design, we observed 3541 men who attended all 4 screenings (1974-1994/1995) and 4993 women who attended the last 3 screenings (1979/1980-1994/1995).
Results: The age- (25-49 years) and sex-adjusted mean BMI increased 1 kg/m(2) in men from 1974 to 1994/1995 and 0.9 kg/m(2)in women from 1979/1980 to 1994/1995. In the last survey, subjects aged 25 to 85 years were included. In most age groups, the mean BMI exceeded 25 kg/m(2) and the prevalence of obesity was 10% or higher in men and women aged 45 years or older. In the longitudinal analysis, the mean BMI in men aged 20 to 49 years increased 2.0 kg/m(2) during 20 years of observation and increased 2.4 kg/m(2)in women aged 20 to 49 years during 15 years of observation. The increase in BMI was larger in younger men than in older men.
Conclusions: Body mass index increased in every examined birth cohort (1925-1964) during the 15- to 20-year observation period. Primary prevention of further increased body weight should be a priority.