Is the relationship between syndromes of depression and dementia temporal? The MRC-ALPHA and Hefei-China studies

BACKGROUND: Recent studies have shown a temporal association between depressive symptoms and cognitive decline. However, the relationship between syndromes of depression and dementia is unknown. METHOD: A total of 1736 people aged > or = 65 years in China and 5222 older people in the UK were interviewed using the Geriatric Mental State Examination (GMS) and reinterviewed at follow-up. Five levels of syndromes of depression and dementia were diagnosed using the Automated Geriatric Examination for Computer Assisted Taxonomy (AGECAT). RESULTS: Although there were fewer depressive syndromes in Chinese than British participants, both populations showed a similarly high level of syndromes of dementia (organic disorder) (20% for women, 14% for men). There was a significant cross-sectional correlation between syndrome levels of depression and dementia (correlation coefficients: 0.141-0.248 for Chinese, 0.168-0.248 for British). This was maintained for different age, gender and people with and without cardiovascular disease (CVD). The relationship between syndromes of baseline depression and follow-up dementia was less substantial: the correlation coefficient was 0.075 95% confidence interval (CI) 0.021-0.128 for the Chinese sample at the 1-year follow-up, and 0.093 (95% CI 0.061-0.125) for the British at the 2-year follow-up and 0.093 (95% CI 0.049-0.130) at the 4-year follow-up. This relationship disappeared in participants without baseline organic syndromes. In a multiple adjusted logistic regression analysis, an increased risk of organic syndromes seemed to be associated with baseline, mainly in the highest level of, depressive syndromes. CONCLUSIONS: The relationship between syndromes of depression and dementia might be temporal. The lack of an obvious dose-response relationship between baseline depressive syndromes and follow-up dementia syndromes suggests that the causal relationship between depression and dementia needs further investigation.