Individual and environmental determinants of body mass index trajectories: results from a longitudinal study in Southern Sweden

Exposure to natural environments is thought to benefit mental and physical health, but current evidence is mixed, and underlying mechanisms remain unclear. Considering the joint biodiversity, climate, and health crises, a better understanding of the interplay between individuals and their environment is imperative. 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, (3) study the associations between natural dimensions of residential environment and BMI trajectories. The SPHC was established in southern Sweden in 2000. Participants (n = 13 581 at baseline, 18–80 years old) responded to four surveys (2000–2016), including sociodemographic, lifestyle and health questions. Residential coordinates were linked to the Scania outdoor Environment Database, which comprised perceived sensory dimensions of residential areas, eight dimensions of the outdoor environment that have previously been identified as important to support people’s health. An adapted version of the Perceived Sensory Dimension Score (PSD3-score) was computed by summing up three dimensions related to the natural environment. Sex-specific BMI trajectories, identified using group-based trajectory modelling, were compared using adjusted multinomial regression. Five BMI trajectories were identified with similar shapes in men and women. Two trajectories started in the normal/overweight categories and were relatively stable over time, while the other three were close to or above the commonly used threshold for obesity. Overall, more favourable socioeconomic and lifestyle factors were observed within non-obese trajectories. The PSD3-score varied geographically across Scania, but for the selected environmental characteristics, little differences were observed in relation to BMI trajectories. For this population, our findings suggest that lifestyle and socioeconomic factors are more important than outdoor environment features for the long-term bodyweight and obesity development.