Association between cumulative average BMI and cognitive decline: a 24-year cohort study

Background: High Body Mass Index (BMI) is linked to poor cognitive performance, yet limited studies have examined the long-term impact of cumulative average BMI (caBMI) on cognitive health. This study explores the association between caBMI and cognitive decline and identifies the critical time window during which caBMI has the strongest association with cognitive decline. Methods: Data were obtained from the Health and Retirement Study (1996–2020). Global cognition was assessed using a standardized composite score of memory and executive function. Cumulative average BMI (caBMI) was computed as the mean of the area under the BMI curve over the follow-up period. Linear mixed models assessed the associations between caBMI and cognitive decline, adjusting for sociodemographic characteristics, lifestyle, and health conditions. Results: Among 8252 cognitively healthy participants (mean age 59.0 [Standard Deviation (SD) = 5.6] years, 58.2% women, mean follow-up 17.5 (SD = 7.0) 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 (−0.0028 SD/year, 95% CI: −0.0034, −0.0021), and memory (−0.0017 SD/year, 95% CI: −0.0023, −0.0011) (all p < 0.001). Year eight was observed as the time point at which caBMI showed the strongest association with declines in global cognition, memory, and executive function. Subgroup analyses revealed that caBMI was associated with greater cognitive decline in older adults (≥ 65 years), compared to the younger adults (50–65 years). Conclusions: caBMI was significantly associated with cognitive decline, with the strongest association observed 8 years later. These findings highlight the importance of long-term weight management and BMI monitoring in cognitive health assessments.