Lifestyle the key to raised CVD risk in depression
The two-year mortality risk for CHD patients is more than doubled if they have symptoms of depression.1 A prospective cohort study from California has found that the association between depressive symptoms and adverse cardiovascular events can be mostly explained by poor health behaviour, especially physical inactivity.
A total of 1,017 participants with stable CHD were followed up for an average of 4.8 years. The PHQ-9 was used to record baseline depressive symptoms. Echocardiography was used to determine baseline disease severity and a number of proposed biological mediators were carefully measured. Potential behavioural mediators were assessed by self-report questionnaires.
Participants with depressive symptoms (PHQ-9 ?10) had an age-adjusted annual rate of cardiovascular events of 10% compared with a rate of 6.7% among the remaining participants (HR 1.50). The HR was reduced to 1.31 after adjustment for comorbid conditions and disease severity.
Confounders or potential mediators were defined as those variables which altered the effect size by more than 5%. Of the potential biological mediators, only C-reactive protein (CRP) levels met this criterion. Adjustment for CRP reduced the HR slightly to 1.24. Of the potential behavioural mediators, smoking and physical activity changed the effect size by 10.9% and a substantial 31.7% respectively. After further adjustment for smoking and exercise, there was no longer a significant association between depressive symptoms and cardiovascular events (HR 1.05).
The 50% greater rate of cardiovascular events for participants with baseline depressive symptoms is low compared with previous studies, but consistent with evidence that the potency of depression as a risk factor may have declined over the past 20 years.3
It is more surprising that no significant association was found between past month major depressive disorder (identified using the Computerised Diagnostic Interview Schedule for the DSM-IV) and cardiovascular events (HR 1.08). It may be that the PHQ-9 is a better measure of physical inactivity than the diagnostic interview.
An underpowered trial of antidepressant treatment post-myocardial infarction found no evidence of benefit 18 months later either in the prevalence of depression or in the incidence of cardiac events.4 The authors of the present study suggest that exercise interventions may prove to be more effective because they directly target an important mechanism linking depression to cardiovascular events.
Perhaps we should abandon screening for depression in CHD patients and replace this with screening for physical inactivity, linked to the provision of local exercise therapy schemes.
Whooley MA, de Jonge P, Vittinghoff E et al. Depressive symptoms, health behaviors, and risk of cardiovascular events in patients with coronary heart disease. JAMA 2008;300:2379-88Reviewer
Dr Phillip Bland