Association between Cumulative BMI and Cognitive Decline: a 24-Year Cohort Study

Background: High Body Mass Index (BMI) is linked to poor cognitive performance, yet few studies have examined the long-term impact of cumulative BMI (cBMI) on cognitive health. This study explores the association between cBMI and cognitive decline and identifies the critical time window when cBMI has the strongest impact. Methods: Data were obtained from the Health and Retirement Study (1996–2020). Cognitive health was assessed using a standardized composite score of memory and executive function. Cumulative BMI was calculated as the area under the curve of BMI over time, and cumulative average BMI (caBMI) was computed as the mean of cBMI values over the follow-up period. Linear mixed models assessed the associations between caBMI and cognitive decline, adjusting for sociodemographic and health factors. Results: Among 8,252 cognitively healthy participants (mean age 58.6 years, 58.3% women, mean follow-up 17.5 years), a 100-unit increase in caBMI was significantly associated with faster cognitive decline: global cognition (-0.0030 SD/year, 95% CI: -0.0036, -0.0024), executive function (-0.0029 SD/year, 95% CI: -0.0038, -0.0021), and memory (-0.0017 SD/year, 95% CI: -0.0023, -0.0011) (all p < 0.001). Year eight was identified as the time point at which the association between caBMI showing the strongest decline rates in global cognition, memory, and executive function. Subgroup analyses revealed that caBMI was related to greater cognitive decline in older adults (≥ 65 years). Conclusions: caBMI was significantly associated with cognitive decline, with the largest impact observed eight years later. These findings highlight the importance of long-term weight management and BMI monitoring in cognitive health assessments.