Adiposity and dementia among Chinese adults: longitudinal study in the China Health and Retirement Longitudinal Study (CHARLS).

Background: Evidence on the age-dependent association between adiposity and risk of dementia in the Chinese population is unclear. We aim to disentangle the association of mid- and late- life adiposity with subsequent dementia risk in Chinese adults and compare ageing trajectories of adiposity between those with/out dementia.

Methods: Dementia was ascertained based on cognitive batteries and the Activity of Daily Living Scale in the China Health and Retirement Longitudinal Study (CHARLS). Adiposity was measured by body mass index (BMI), waist circumference (WC), and waist-to-height ratio (WtHR). We estimated hazard ratio (HR) of adiposity for incident dementia by age groups (i.e. 50-64, and ≥65). Age trajectories of adiposity measures were fitted using a mixed-effect model in a case-control design. The interaction terms of age and dementia were included to examine the difference between cases and controls.

Results: Hazard ratios (HRs) for incident dementia in two age groups (50-64 and ≥65) were estimated in 13,355 participants. Raised mid-life BMI was associated with incident dementia (HR (95% CI): overweight 1.33 (1.03 to 1.73), obesity 1.63 (1.17 to 2.28)). Mid-life abdominal obesity was associated with incident dementia (WC 1.45 (1.15 to 1.84), WtHR 1.44 (1.08 to 1.94)), accounting for ≤24.2% of dementia cases. Among participants developing dementia, adiposity measures were higher in mid-life and declined faster with age, compared to those remaining dementia-free. Late-life adiposity was not associated with dementia risk.

Conclusion: Mid-life but not late-life adiposity was associated with dementia incidence in China. Accelerated weight loss in prodromal dementia is likely to explain the mixed evidence on adiposity and dementia risk in the Chinese population. Rapid decline in adiposity in later life may be an early sign. Reducing mid-life adiposity in the population may mitigate the future dementia burden.