It isn't called a broken heart for nothing. Numerous studies have found an association between depression and cardiac problems, including arrhythmias, heart attacks, strokes, etc. Some studies have found associations between worsening outcomes in heart disease in patients who develop depression (for example, depression following a heart attack) while others have found such worsened outcomes simply if one has a history of depression-even if the depression happened years ago..
Surveying 10000 people over the age of 60, a recent study found that a single episode of depression at any point in one's life predisposed the individual to future coronary heart disease. Surprisingly, the number of episodes did not change the risk-having one depression was as bad as having six. What was also surprising was how significant the association was. Nicotine use and obesity both increase the risk of heart disease one and a half times, but depression was found to be even worse than those conditions-it doubled the risk.
If you want a further surprising result, it is this: anxiety disorders did not increase the risk.
What are the possible explanations? One could be that depression causes an increase or decrease in cardiac-related chemicals: for example, depression increases stress hormones and inflammatory cytokines, both which can facilitate heart disease. An alternative explanation is that it is what depression causes you to do that leads to heart disease.
It appears that there are two important parameters that determine the risk between depression and heart disease: first, whether the cardiac disorder is sudden and acute (such as a heart attack), or stable and chronic (such as ongoing coronary atherosclerosis.) The next parameter is the subtype of depression that predominates: somatic or cognitive. Somatic symptoms include poor sleep and poor appetite, while cognitive symptoms include feelings of guilt and the inability to enjoy pleasurable experiences (known as anhedonia).
Looked at in this way, it appears that somatic symptoms have an association with acute cardiac pathology, while cognitive symptoms are associated with chronic conditions.
This would be useful information. For example, certain types of medications are better at treating somatic symptoms, and others are better for cognitive symptoms. But there was one additional finding in the recent research: when lifestyle factors that predispose cardiac problems (such as smoking, obesity, male gender, poor diet, poor exercise, etc.) were controlled, the association between somatic symptoms and heart rate effects in coronary heart disease disappeared. In other words, it was these other comorbidities that led to the somatic symptoms of depression.
So the take home points are these: depression leads to heart disease in some way, either directly or indirectly, and even one episode can be harmful. Depression may also predispose one to behaviors which lead to cardiac disease: smoking, overeating, sedentary lifestyle, etc. Finally, having certain lifestyles and behaviors which can predispose to cardiac disease may also lead to depression itself.