Re: Depression as a risk factor for ischaemic heart disease in men: population based case-control study
Hippisley-Cox et al. conducted a case control study suggesting that depression is linked to ischaemic heart disease (IHD). It is obviously important to consider whether this link actually exists. We do, however, question the validity of the result of this study. Our two main concerns are: firstly, considering all important confounding variables, and, secondly, the relative timing of the two diagnoses.
There is some evidence that obesity is linked to both depression and IHD, and thus omitting BMI from the multivariate analysis may confound the results. Obviously, collection of data on BMI has been a limitation of a case control study. Another problem with the design has been the exact timing of diagnosis of IHD and depression, where the diagnosis of IHD and depression was assumed to precede that of depression if both occurred in the same year.
Therefore, we suggest that a prospective study following patients with depression will be a more appropriate study design. This will enable all relevant data to be collected, accounting for differences in BMI and other factors such as exercise, family history and serum lipids. This will also ensure that for each case the diagnosis of depression precedes that of IHD.
Bisher Kawar, Richard Latham and Alison Macrae
Department of Epidemiology and Public Health, University of Newcastle.
Tel. 0191 222 8754
Fax. 0191 222 8211
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Competing interests: No competing interests