Historic trends and future projections of the prevalence of adult excess weight in Scotland, 2003 to 2040: a Bayesian age-period-cohort modelling study

IntroductionThe prevalence of excess weight in Scotland is higher than other UK nations and amongst the highest when compared with European Union countries. The aim of our study was to use historic data to identify and integrate age-period-cohort (APC) effects into projected estimates of the prevalence of excess weight in Scotland. MethodsInterviewer-validated height and weight measurements were obtained for 72,542 adults between 2003 and 2019 from the Scottish Health Survey to calculate body mass index (BMI). Relevant socio-demographic data were also sourced to contribute to modelling and results stratification. Study outcomes were defined as prevalent cases of overweight (BMI [≥] 25) and obesity (BMI [≥] 30). We estimated historic trends in study outcomes by sex and age-group, and projected future trends to 2040, using Bayesian hierarchical APC modelling. ResultsIn 2040, we estimate 3.2 million prevalent adult cases of overweight, of which 1.5 million are cases of obesity. Projections were more pronounced for obesity, compared to overweight, with around an additional 32,000 male cases and 133,000 female cases between 2019 and 2040. Between 2003 and 2019, the proportion of male and female cases of both overweight and obesity aged 65 years and above have increased, a trend projected to further intensify as we move towards 2040. ConclusionLeft unaddressed, we estimate a substantial increase in adult excess weight in Scotland by 2040, particularly for females, compounded by increases in obesity and in the proportion of older cases. These findings are a warning signal of future adverse population health impacts and healthcare service sustainability pressures. Projected estimates are not inevitable and underscore the need to accelerate progress on implementing preventative measures to address the food environment, and on further development of weight management and support services, to improve the health and wellbeing of the Scottish population. Key messagesO_ST_ABSWhat is already known on this topicC_ST_ABSO_LIThe prevalence of excess weight in Scotland is higher than other UK nations and amongst the highest when compared with European Union countries. C_LI What this study addsO_LIIn 2040, we estimate approximately 3.2 million prevalent adult cases of overweight in Scotland, of which 1.5 million are cases of obesity. C_LIO_LIOur study highlights that projections were more pronounced for obesity, compared to overweight, with around 32,000 additional male cases and 133,000 additional female cases between 2019 and 2040. C_LIO_LIUnderpinning these findings were major shifts in the age distribution of cases. Between 2003 and 2019, the proportion of male and female cases of both overweight and obesity aged 65 years and above have increased, a trend projected to further intensify as we move towards 2040. C_LI How this study might affect research, practice, or policyO_LIOur public health foresight study provides insights into a possible future. These findings are not inevitable and underscore the need to accelerate progress on implementing preventative measures to address the food environment, and on further development of weight management and support services, to improve the health and wellbeing of the Scottish population. C_LI