Environmental determinants of body mass index trajectories: results from a longitudinal Swedish study

Exposure to natural environments is thought to benefit mental and physical health. A better understanding of the interplay between the individual and the environment in relation to public health is imperative in light of the joint biodiversity, climate, and health crises. This study aimed to 1) identify Body Mass Index (BMI) trajectories in the Scania Public Health Cohort (SPHC), 2) characterise trajectories in terms of sociodemographics, lifestyle, health and living environments and 3) study the associations between BMI trajectories and green qualities of the environment. The SPHC was established in southern Sweden (Scania) in 2000. Participants (n = 13581 at baseline, 18-80 years old) responded to 4 surveys (2000-2016) including questions on sociodemographics, lifestyle and health. Residential coordinates were linked to the Scania Outdoor Environment Database (ScOut) comprising perceived sensory dimensions. “Diverse”, “serene” and “natural” dimensions were summed up to obtain the Scania Green Score. Sex-specific BMI trajectories, identified using group-based trajectory modeling, were compared using multinomial regression, adjusted for main confounders. Five trajectories were identified with similar shapes in men and women. Stable-normal (1) and stable-overweight (2) trajectories exhibited slow linear BMI increase. Fluctuating-overweight (3) and fluctuating-obesity (4) trajectories showed BMI increase followed by decrease, starting from overweight or obesity. The increasing-obesity (5) trajectory showed a persistent increase towards obesity. Trajectories were associated with socioeconomic and lifestyle factors. The highest proportions of university education and lowest proportions of sedentary lifestyle were found in the stable trajectories (1-2). Economic strain was highest in (5). Preliminary analyses showed no clear associations between Scania Green Score at baseline and trajectory membership. BMI trajectories were associated with socioeconomic and lifestyle factors.