It is estimated that depressed people with heart disease are 70% more likely to experience coronary events (e.g., heart attack , death) than people who are not depressed. In fact, depression has recently been listed as one of the nine major modifiable risk factors for heart attack worldwide. While it is clear that depression increases the risk of adverse outcomes in people with heart disease, researchers do not yet know why.

In two new studies—one in the November 28, 2005 issue of the Archives of Internal Medicine and another in the November 2005 issue of the American Journal of Psychiatry —researchers attempted to identify possible reasons for the link between depression and adverse outcomes in heart disease patients. They found that those who were depressed were more likely to skip their medications and have elevated levels of the stress hormone, norepinephrine, than those who were not depressed.

About the Study

Both studies examined patients from the Heart and Soul study, which is looking at the relationship between psychological factors and health outcomes in people with heart disease. All of the participants had been diagnosed with heart disease and took part in a day-long examination that included a health interview, cardiac testing, and a 24-hour urine sample collection. In these studies, researchers adjusted their analyses for other factors thought to contribute to the risk of heart disease complications, including age, ethnicity, education, social support, and heart disease severity .

The first study ( Archives of Internal Medicine ) evaluated medication adherence in 940 participants, 22% of whom were depressed. The researchers asked the participants how often they took their medications as prescribed. They found that, compared to non-depressed participants, depressed patients were more than twice as likely to take medications incorrectly, forget to take them or decide to skip them.

In the second study ( American Journal of Psychiatry ), researchers examined the levels of the stress hormones norepinephrine, epinephrine, and dopamine in the urine samples of 598 participants, 18% of whom were depressed. They found that depressed participants had higher levels of norepinephrine than participants who were not depressed. Thirty-two percent of the depressed participants compared with 23% of non-depressed participants had the highest levels of norepinephrine. Depression was not associated with epinephrine or dopamine levels.

Both studies were limited because they relied on the participants’ recollection of their medication adherence and compliance with the collection of urine samples. And neither study could determine whether skipping medications or high levels of norepinephrine causes coronary events, only that they are more prevalent in depressed patients.

How Does This Affect You?

These studies suggest that, among patients with heart disease, poor medication adherence and high levels of the stress hormone, norepinephrine, are more common in those who suffer from depression. While the cause of the higher risk of coronary events in depressed heart disease patients is still unclear, it is certainly plausible that skipping medications and being stressed could increase the risks of heart attacks and death.

All patients with heart disease and their families should be watchful of signs of depression, which should never be taken lightly. The good news is that depression can be safely and effectively treated in patients with even advanced heart disease. If you or a member of your family seems depressed, do not ride it out. Talk with your doctor, who can evaluate and treat your symptoms, or refer you to someone who can help.