Intra-individual changes in body weight in population-based cohorts during four decades: the Finnish FINRISK study.

Background: The aim of the study was to evaluate trends in intra-individual weight changes over the last four decades in Finland.
Methods: Within the eight FINRISK surveys conducted during the years 1972-2007, we identified individuals who had participated, by chance in at least two surveys. First, individuals aged 25-54 years who had undergone a health examination within 10 years of the first examination (n = 2033) were categorized into five cohorts covering different time periods, and the annual weight change was calculated at follow-up. Second, for each individual aged 25-69 years the longest possible follow-up time (5-35 years) was identified (n = 3443), and the corresponding annual weight change was evaluated.
Results: Comparing the five cohorts from different time periods, the annual increase in body weight among men between 25- and 54-year old remained stable in the range of 0.27-0.47 kg per year over the decades, whereas women belonging to the most recent cohorts (the 1990s) gained weight at 0.53-0.63 kg per year, which is more than double the oldest cohort's weight gain of 0.24 kg. Overall, the annual increase in weight was around 0.3 kg in both sexes. The younger participants had a stronger tendency to gain weight than the older, and those with BMI < 25 kg/m(2) gained more than overweight or obese individuals.
Conclusion: The amount of intra-individual annual increase in body weight among men remained stable over the decades, while it increased among women. The tendency to gain weight was most pronounced among the youngest and among those initially leanest.