MONTREAL — Primary care patients with asthma face a significantly increased risk of developing depression, compared with the nonasthmatic population, according to the findings of a large, longitudinal study.
Furthermore, the combination of asthma and depression carries significantly increased mortality, reported Dr. Paul Walters of the Institute of Psychiatry, King's College, London.
Taken together, the findings suggest that it may be useful for family physicians to consider screening their asthmatic patients for depression, he said at the annual meeting of the North American Primary Care Research Group.
In a previous study, Dr. Walters and his colleagues found that asthma was the third-largest predictor of antidepressant prescriptions in the United Kingdom (Br. J. Psychiatry 2008; 193:235–9).
“We expected there to be a higher rate of antidepressant use with chronic illnesses, but we didn't expect to see this with asthma,” he said.
The current longitudinal cohort study, designed to explore the association between asthma and depression, identified 11,275 asthmatic patients with no history of depression and an equal number of control subjects, matched for age and sex from the United Kingdom's General Practice Research Database.
During a 10-year follow-up period, the incidence of depression was significantly higher in the group with asthma, compared with controls (22.4 versus 13.8 per 1,000 person-years); after adjustment for age, sex, chronic illness, and smoking, the odds ratio for depression among asthmatic patients remained elevated (1.5).
Looking next at the asthmatic patients only, the researchers noted those with comorbid depression had an elevated mortality ratio (1.87), compared with those with asthma alone. “So, if you've got asthma and you're depressed, then you're almost twice as likely to die than if you've just got asthma,” explained Dr. Walters.
He acknowledged that “we don't have any information on cause of death, so we're not able to say if it was due to asthma-related reasons or depression-related reasons or a combination of both.”
For clues as to why asthmatic patients face a higher risk for depression, the researchers explored the issue of disease severity, using medication use as a marker. Comparison of asthmatic patients who were depressed to those who were not depressed showed no significant differences in the use of medication overall, suggesting that disease severity was similar in both groups, he said.
The biggest difference between the groups was in their frequency of primary care visits (8.3 visits a year for depressed patients versus 5.3 for nondepressed patients). One possible explanation for this association may be that “if a patient goes to their [general practitioner] more often, they're more likely to get their depression diagnosed,” Dr. Walters said in an interview.
Another explanation, however, is that a patient's subjective experience of asthma symptoms might be quite different from objective medical assessments. “It could be that the objective measure of asthma, the peak flow rate, doesn't actually relate to how the person with asthma feels, so the depression comes because their asthma doesn't feel like it's getting better.”
Dr. Walters had no conflicts of interest to report.