Reason to be Happy
Chronic depression may rob you of more than joy: the evidence is piling up that it can also steal your health
What might explain the mind's influence on physical health? Certainly, chronic depression does not encourage a healthy lifestyle. "Depressed individuals don't exercise. They are more likely not to take medication, and it is harder for them to lose weight and stop smoking," says Nancy Frasure-Smith, a professor of psychiatry at the University of Montreal and McGill University who has long studied the link between depression and cardiovascular disease.
The biochemistry. But depression also acts on the body's systems in ways scientists are only beginning to understand. Extra stress hormones are produced, for example--along with chemicals that trigger inflammation. When the hormone cortisol is secreted in response to stress, the body's blood glucose level rises to provide a burst of energy. A depressed brain's constant signal that it's under stress and needs more energy complicates the body's regulation of blood sugar. Might this explain why depression seems to both trigger and exacerbate diabetes?
A stress response may set depressed people up for cardiovascular disease, too--or aggravate it. When the blood-clotting system gets ready for impending injury, sticky cells called platelets go on high alert to slow down bleeding. In depressed people, one study showed, the platelets are more apt to be in this state of readiness. The problem: Clotting is what causes heart attacks and strokes. Chemicals called cytokines flood the bloodstream, as well. These messengers from the immune system cause inflammation, which makes blood vessels thicken and artery-hardening plaques form.
Researchers have also noted another stress reaction: The heart muscles of depressed patients lose flexibility. A normal heart transitions easily between its resting and beating states; more rigid muscle is less able to respond to the changing demands of the body for blood and oxygen. A study published last month in the Journal of the American College of Cardiology found that mental stress caused a more dramatic decrease in blood flow to the heart muscle--or ischemia--than a stress test on a treadmill. All told, stress and depression probably explain "close to 30 percent of the total risk of heart attacks," estimates David Sheps, professor of medicine and associate chief of cardiovascular medicine at the University of Florida.
It's way too soon to make the leap that depression is a direct cause of heart disease akin to smoking or high cholesterol, or that treatment--like quitting cigarettes--can reverse the damage or save lives. Indeed, two big recent studies have failed to show that heart patients live longer when they undergo therapy or take antidepressants. But medicine is intent upon dealing with the mental health of cardiac patients anyway, because people who are not depressed are more likely to lead heart-healthy lives; they exercise, take their medicines, lose weight, and stop smoking. "If you are a patient with heart disease, you need to know what your cholesterol level is, what your blood pressure is, and what diet and exercise program you will need to prevent a second heart attack. You should add to that list whether or not you are depressed," says Richard Stein, director of preventive cardiology at Beth Israel hospital in New York.
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