Severity of depression and risk for subsequent dementia: cohort studies in China and the UK

BACKGROUND: Depression and dementia often exist concurrently. The associations of depressive syndromes and severity of depression with incident dementia have been little studied. AIMS: To determine the effects of depressive syndromes and cases of depression on the risk of incident dementia. METHOD: Participants in China and the UK aged > or =65 years without dementia were interviewed using the Geriatric Mental State interview and re-interviewed 1 year later in 1254 Chinese, and 2 and 4 years later in 3341 and 2157 British participants respectively (Ageing in Liverpool Project Health Aspects: part of the Medical Research Council - Cognitive Function and Ageing study). RESULTS: Incident dementia was associated with only the most severe depressive syndromes in both Chinese and British participants. The risk of dementia increased, not in the less severe cases of depression but in the most severe cases. The multiple adjusted hazard ratio (HR)=5.44 (95% CI 1.67-17.8) for Chinese participants at 1-year follow-up, and HR=2.47 (95% CI 1.25-4.89) and HR=2.62 (95% CI 1.18-5.80) for British participants at 2- and 4-year follow-up respectively. The effect was greater in younger participants. CONCLUSIONS: Only the most severe syndromes and cases of depression are a risk factor for dementia.