Impact of body roundness index on cognitive decline and cognitive impairment in middle-aged and older adults ≥ 45 years: mediating role of biological aging

Abstract

Abstract The relationship between Body Roundness Index (BRI) and cognitive function in middle-aged and older adults remains unclear. We aimed to explore the association of BRI with cognitive trajectories and incident cognitive impairment and the mediated effect of biological aging. A subset of 8,595 participants (aged 57.71 ± 8.48 years, 52.71% men) from China Health and Retirement Longitudinal Study (CHARLS) were followed up to 9 years. BRI was calculated based on height and waist circumference. Cognitive function was assessed with neuropsychological tests up to 5 times, and cognitive impairment was defined as scoring 1.5 standard deviations below the mean. Biological aging was evaluated using the Klemera-Doubal method for biological age (KDM-BA). Linear mixed-effects models were used to explore the effect of BRI on the annual change in cognitive function. Cox regression, Laplace regression and restricted cubic spline models were used to assess the association between BRI and the occurrence of cognitive impairment. Mediation analyses was performed to assess the role of biological aging in these relationships. During the follow-up, 1,282 (14.9%) developed cognitive impairment. Higher BRI was also associated with a faster decline of global cognition ( β  = − 0.009, 95% confidence interval [CI]: − 0.017 to − 0.007), especially executive function and temporal orientation over time (all P  < 0.05). The multi-adjusted hazard ratio (HR) (95% CI) of BRI for cognitive impairment was 1.12 (1.05–1.19). Each unit increased in BRI led to a 0.41-year earlier onset of 15th percentile difference (PD) in cognitive impairment (95% CI: 0.13–0.68). A J-shaped dose–response relationship on the risk of cognitive impairment was identified with an inflection point of BRI at 4.61. The mediation proportion of BRI affecting cognition decline and occurrence of cognitive impairment through KDM-BA after adjustment was 47.18% and 10.19%, respectively. These findings suggest that levated BRI accelerated the progression of cognitive decline and increased the risk of cognitive impairment onset in middle-aged and older adults. Biological age may partially mediate the association.