Association of body mass index, waist circumference, (abdominal) overweight and obesity with sex- and age-specific cognitive function over time—the Doetinchem Cohort Study

Background: Having obesity is a risk factor for cognitive decline and dementia. It remains unclear whether timing of obesity during someone’s lifespan affects this association. Aim: To study the association of body mass index (BMI), waist circumference (WC), and having (abdominal) overweight and obesity with cognitive function and decline, and whether these associations were modified by age. Methods: 3873 participants (aged 45–70 at baseline, 52% women) from the Doetinchem Cohort Study were included, with up to six repeated measures. Participants were classified as having (abdominal) obesity if they had a BMI ≥30 kg/m² or WC ≥102 cm (men) or ≥88 cm (women). Domain scores for global cognition, memory, flexibility, and processing speed were calculated by standardizing individual test scores at baseline. Associations of time-dependent BMI, WC, and (abdominal) overweight and obesity with cognitive function and decline were studied using linear mixed models. Models were sex-stratified and adjusted for socio-demographic, lifestyle, and mental health factors. Modification by age (≤ or >55 years at baseline) was evaluated using interaction terms. Results: Higher BMI and WC were associated with worse level of cognition (all domains). For both sexes, the smallest difference was for global cognition (BMI) and processing speed (WC), the largest for flexibility (BMI) and memory (WC). Furthermore, having (abdominal) obesity, compared to a healthy BMI/WC, was consistently associated with worse memory function in both sexes. Effect sizes were generally larger for categorical WC compared to categorical BMI. In men, abdominal obesity was associated with accelerated decline in processing speed (all ages), and with accelerated decline in global cognition and flexibility (> 55 years). Conclusions: In both sexes, higher BMI and WC were consistently associated with worse cognition. WC-based overweight and obesity showed larger effect sizes with cognition than BMI-based overweight and obesity. Only in men, associations with cognitive decline and effect modification by age were observed.