Trends in all-cause and cause-specific mortality by BMI levels in England, 2004-2019: a population-based primary care records study.

Background: In the UK, obesity rates are rising concurrently with declining mortality rates. Yet, there is limited research on the shifts of mortality trends and the impact of obesity-related mortality. In this study, we examine mortality trends and the cause-specific proportional composition of deaths by body mass index. Methods: We used primary healthcare records from the Clinical Practice Research Datalink between 2004 and 2019, linked to national death registration data. There were 880,683 individuals with at least one BMI measurement and a 5-year survival period. We used discrete Poisson regression and joinpoint analysis to estimate the all-cause and cause-specific mortality rate and significance of the trends. Findings: Between January 1, 2004, and December 31, 2019, all-cause mortality rates declined in the obese category by 3% on average per year (from 23.3 to 14.6 deaths per 1000 person years) in males and 2% on average per year (from 12.5 to 9.4 deaths per 1000 person years) in females. Cardiovascular disease mortality declined 7% on average per year (from 12.4 to 4.4 deaths per 1000 person years) in males and 4% on average per year (from 5.5 to 3.0 deaths per 1000 person years) in females in the obese category. Increases in mortality rates from neurological conditions occurred in all BMI categories in males and females. By the end of the study, cancers became the primary contributor of death in males in all BMI categories and females in the overweight category. Interpretation: There have been significant declines in all-cause and cardiovascular disease mortality in males and females, leading to a diversification of mortality, with cancers contributing to the highest proportion of deaths and increases in causes such as neurological and respiratory conditions. Further screening, prevention, and treatment implementation for a broader set of diseases is necessary for continued mortality improvements. Funding: Imperial College London, Science Foundation Ireland.