Body mass index increases differently in population subgroups: projections for Finland to 2040

Abstract Background Obesity is an increasing public health concern globally. In Finland, obesity has become notably more prevalent over the past decades. In this study, we analysed trends in the distribution of body mass index (BMI) and its categories (normal weight, overweight, obesity) among the Finnish population by sex, age (25-44 and 45-65 years) and educational groups (low, medium and high) from 1997 to 2023, and projected these trends up to 2040. Methods Data were obtained from six cross-sectional health examination surveys conducted between 1997 and 2023 (n = 30,441). BMI was derived from measured height and weight. The analysis was stratified by sex, age group and educational level. Projections to 2040 were made using a multiple imputation approach with polytomous regression models based on historical trends and national population forecasts. Results BMI increased in all subgroups, but not evenly across the BMI distribution. The proportion of individuals with high BMI values increased rapidly, while the share of those with low BMI remained almost the same. The trends in obesity were increasing among women and men aged 25-44 and 45-64 years and across all educational groups. Obesity remained more prevalent among those with low education, from 1997 to 2023, but the recent increase among highly educated women was so steep that, if the trend continues, both low- and high-educated women will have obesity prevalences of around 45% by 2040, whereas middle-educated women will have only around 27%. Low-, middle- and high-educated men would have obesity prevalences of around 38, 45 and 31% in 2040, respectively. Conclusions The increasing trends in obesity pose significant challenge for public health in Finland. These subgroup-specific findings highlight the need for targeted measures to address obesity. Effective public health strategies and policies are essential to mitigate the future burden of obesity-related health concerns, especially among young adults. Key messages • The study highlighted the growing obesity problem in Finland, with BMI increasing across all examined subgroups. • Targeted public health strategies are needed to address obesity, especially among young adults.