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PAPERS:
Ruoling Chen, Zhi Hu, Li Wei, Xia Qin, Cherie McCracken, and John R. Copeland
Severity of depression and risk for subsequent dementia: cohort studies in China and the UK
The British Journal of Psychiatry 2008; 193: 373-377 [Abstract] [Full text] [PDF]
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[Read eLetter] Depression and dementia
Shubh M Singh   (6 November 2008)

Depression and dementia 6 November 2008
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Shubh M Singh,
Assistant Professor, Psychiatry
Gian Sagar Medical College, Banur, Punjab, India-140601

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Re: Depression and dementia

shubhmohan{at}gmail.com Shubh M Singh

Chen et al (1) conclude that a dose-response association exists between severity of depression and the risk of subsequent development of dementia. However certain methodological issues need to be considered. Firstly, were the Chinese and British cohorts comparable? As per Copeland et al (2), the patients in the MRC-ALPHA study were drawn from family practitioner lists and included those living in nursing homes whereas the Chinese cohort was derived wholly from the community. The nature of the British cohort would suggest a predisposition to increased rates of physical and depressive comorbidity even before entry into the study. Secondly, are the numbers enough? For instance, the Chinese cohort had only 4 patients with level 4 depression out of which 3 developed dementia. While, the HR is 5.05, the CI is quite wide (1.56-16.3). The conclusions drawn should be supported by a power analysis as there may be a danger of a type 1 error in concluding that severity of depression is related to subsequent dementia. Thirdly, organic syndromes were significantly more prevalent in those with level 4 depression as compared to those with level 3 depression in the MRC-ALPHA patients. When these cases are excluded, the CI of the HR for level 1, 2 and 3 depression overlap (level 1: 0.84-2.21, level 2: 0.52-1.40, level 3: 0.53-1.44 and level 4: 1.00-3.57) which would indicate that while the differences in subsequent development of dementia in patients with differing severity of depression are suggestive, these are not significant. The development of subsequent dementia may have been related to the pre-existing and progressive organic insult rather than depression per se. While this study is important and timely, the results and implications thereof are suggestive rather than conclusive.

1. Chen R, Hu Z, Wei L,Qin X, McCracken C, Copeland JR. Severity of depression and risk for subsequent dementia: cohort studies in China and the UK Br J Psychiatry. 2008;193:373-7. 2. Copeland J, McCracken C, Dewey ME, Wilson KC, Gilmore C, Scott A, Larkin BA. Undifferentiated dementia, Alzheimer's disease and vascular dementia: age- and gender-related incidence in Liverpool. The MRC-ALPHA Study. Br J Psychiatry. 1999;175:433-8.