Sex-Differential Associations Between Body Mass Index and the Incidence of Dementia

Little is known about the sex differences in the association between body mass index (BMI) and dementia in late life.

Therefore, this retrospective cohort study aimed to analyze associations between BMI and dementia in older women and men separately in general practices in Germany.

This study included patients followed in one of 832 general practices in Germany between 2006 and 2019 (index date: first visit date). Study variables included dementia (dependent variable), BMI (independent variable), age, sex, and comorbidities (control variables). Kaplan-Meier curves and adjusted Cox regression analyses were conducted to analyze associations between BMI and the 10-year incidence of dementia in women and men, separately.

There were 296,767 patients included in this study (mean [standard deviation] age 70.2 [5.9] years; 54.3% women). The proportion of underweight, normal weight, overweight, and obesity was 0.9%, 25.5%, 41.5%, and 32.1%, respectively. The 10-year incidence of dementia significantly decreased with increasing BMI, from 11.5% in women with underweight to 9.1% in those with obesity (log-rank p < 0.001). Respective figures in men were 12.0% and 8.2% (log-rank p < 0.001). In women, only overweight (versus normal weight) was significantly associated with dementia (HR = 0.93, 95% CI = 0.88-0.97). In contrast, in men, the only BMI category significantly associated with the incidence of dementia was underweight (HR = 1.58, 95% CI = 1.11-2.25).

In this study conducted in Germany, overweight was negatively associated with dementia in women, whereas there was a positive underweight-dementia relationship in men. More data are needed to confirm or refute these findings in other settings.