Independent and combined effects of depressive symptoms and cardiometabolic risk factors on dementia incidence: a cross-country comparison in England, the United States and China.

BACKGROUND

Depression and cardiometabolic conditions are suggested as modifiable risk factors for dementia, yet their combined impact remains unclear. This study assessed the independent and combined effects of depressive symptoms and cardiometabolic conditions on dementia incidence in England, the US and China.

METHODS

The sample comprised 4472 participants aged 50 and older from the English Longitudinal Study of Ageing (ELSA), 5021 from Health and Retirement Study (HRS), and 8925 from China Health and Retirement Longitudinal Study (CHARLS). Depressive symptoms were assessed using the Center for Epidemiological Studies-Depression scale. Cardiometabolic factors included central obesity, low high-density-lipoprotein (HDL) cholesterol, systolic and diastolic blood pressure (BP), hyperglycemia, diabetes, and inflammation. Dementia incidence was estimated using confounder-adjusted Cox proportional hazards regressions, and pooled estimates were obtained using random-effects meta-analysis.

RESULTS

A total of 1218 individuals developed dementia over a median of 6.8-12.2 years. Depressive symptoms (ELSA: HR = 1.47 [95 % CI = 1.09-2.00]; HRS: HR = 1.68 [95 % CI = 1.33-2.13]; CHARLS: HR = 1.35 [95 % CI = 1.12-1.64]) and elevated systolic BP (ELSA: HR = 1.51 [95 % CI = 1.17-1.95]; HRS: HR = 1.48 [95 % CI = 1.24-1.79]; CHARLS: HR = 1.26 [95 % CI = 1.05-1.52]) were linked to dementia risk in all countries. While cardiometabolic multimorbidity (≥2 conditions) was not associated with dementia risk, those with the highest cardiometabolic index (≥4 conditions) had a greater risk of dementia in all samples (ELSA: HR = 1.82 [95 % CI = 1.01-3.26]; HRS: HR = 1.85 [95 % CI = 1.02-3.35]; CHARLS: HR = 1.65 [95 % CI = 1.18-2.30]).

CONCLUSION

Depressive symptoms are independently linked to dementia risk, while having multiple cardiometabolic conditions further increases this risk, especially when co-occurring with depressive symptoms in both Western and Chinese populations.