As if anyone needed more proof that life is unfair: It is becoming increasingly clear that depression not only makes you feel miserable, but can also damage your heart.
On top of that, a heart attack or other cardiovascular ailments can trigger depression.
Together, the conditions can significantly increase your chances of dying. Chronic depression doubles the probability of having a first heart attack or stroke. "That's about the same risk as smoking," says Dr. Daniel Ford, a professor at the Johns Hopkins School of Medicine and an expert on mental health and heart disease.
People who have a heart attack and then become depressed are three times more likely to die than patients without melancholy. And studies that show 30 percent to 40 percent of heart attack patients, and half of those who undergo bypass surgery, subsequently get depressed.
Yet many doctors and patients remain unaware of the heart-head connection, and post-heart attack depression remains seriously underdiagnosed. This week, the Journal of the American Medical Association published a review of the subject to remind doctors of the close relationship between the two conditions.
"Cardiologists tend to ignore the possibility of depression. I think that's a fundamental mistake," says Dr. Mandeep R. Mehra, chairman of the cardiology department at the University of Maryland Medical Center. To help change this, he will soon unveil a behavioral cardiology program to focus on the psychological and psychiatric facets of heart disease.
The topic received attention last week as a result of the suicide of prominent publisher Philip Merrill. The 72-year-old former diplomat had undergone bypass surgery last year. His family indicated that he was apparently despondent over the deterioration of his health. It is not clear, however, whether his plummeting mood was directly related to the heart procedure.
The links between heart and brain remain mysterious, but scientists are beginning to unravel the relationship. Among the culprits are inflammation, dysfunctional neurotransmitters, excess stress hormones and that old standby, existential dread.
Part of the explanation is probably behavior: Depressed people tend not to take good care of themselves. They smoke more, drink more alcohol, exercise less, and are more obese than those without depression. "People who are depressed engage in all kinds of behavior that is unhealthy," says Willem J. Kop, a psychologist at the Uniformed Services University of the Health Sciences in Bethesda.
And after a heart attack, many patients become fully aware for the first time of their own mortality. The prospect of death, and fear that the damaged heart will significantly constrict one's remaining life, can cause deep unhappiness.
"The individual is facing the grim reaper," says Dr. Douglas Clarke, a cardiologist at St. Joseph Medical Center in Towson. "This is a paradigm shift. It's a real life-changer."
But depression after heart disease is not solely because of psychological crisis. Scientists studying the topic suspect that heart attack and heart disease may subtly damage the brain, making some people more vulnerable to depression. University of Maryland at Baltimore County psychologist Shari Waldstein, who studies cardiovascular disease and the brain, says a heart ailment can impair blood flow to the brain. "The brain doesn't get enough oxygen or nutrients," she says.
Others suspect that post-heart attack depression may stem from a flood of inflammatory proteins. During and after an attack, the body releases large amounts of inflammation-triggering molecules. These substances tell the body that a serious injury has occurred, and also help the healing process.
Some scientists think that depression after heart attack may be an adaptive reaction by the body, an attempt to ensure that the injury isn't worsened through overexertion. "[The depression] may be a mechanism to keep the animal from venturing out," says University of Washington psychology professor Wayne Katon.
Studies have found that people with depression have increased levels of some inflammatory chemicals. "These proteins may actually evoke a behavioral response characterized by lack of interest and lethargy," says Duke University psychologist Edward Suarez.
Dr. Nancy Frasure-Smith, a professor of psychiatry at McGill University in Montreal, is among those who think inflammation plays a key role. In a study published last year in the American Journal of Psychiatry, she found that depressed heart attack patients have higher levels of certain inflammatory chemicals than heart attack patients who were not depressed. "Inflammation may in fact create symptoms of depression," she says.
Researchers have made more progress in teasing out the other side of the issue, how chronic depression can lead to heart disease. The two conditions share many features and, in some people, may have a common origin.
Here, too, inflammation may play an important part. Even in the absence of prior heart disease, depression alone seems to produce low-level inflammation throughout the body. Over the course of years or decades, this condition can damage blood vessels, and eventually, the heart itself.
"The more inflamed your system is, the more likely you are to have atherosclerosis," says Kop. Atherosclerosis, hardening of the arteries, often leads to heart attack because the organ must work harder to pump blood to narrowed vessels, and because stiffened pieces of the vessel wall can break off to form blood clots.
Depression also affects the heart in other ways. Those with the illness tend to constantly produce high levels of cortisol, a hormone that puts the body on alert for an imminent threat. In the face of real danger, cortisol is useful: it speeds up heart rate, helps the body conserve energy and increases alertness. But the hormone becomes harmful when it inundates the body regularly, as happens in depression. It can cause high blood pressure, and increase levels of insulin, abdominal fat and "bad" cholesterol, all of which damage the cardiovascular system.
"Chronically high cortisol is bad for your heart," says Carol Shively, a psychologist at the Wake Forest University School of Medicine in Winston-Salem, N.C.
She is focusing her work on another potential explanation: serotonin. For decades, scientists have known that many if not most people with depression have unusually low levels of this neurotransmitter. (Antidepressants such as Prozac work by increasing the amount of serotonin available to the brain.) Increasingly, researchers are discovering that serotonin may also affect the cardiovascular system. Low serotonin levels seem to raise heart rate, which could contribute to heart disease by increasing blood pressure.
Shively studies depressed macaques. She has found that these monkeys have reduced serotonin in the brain areas that control mood, as well those that regulate heart rate.
"High heart rate and low serotonin are closely associated with one another," she says. Over years, these low-serotonin animals tend to develop atherosclerosis.
Serotonin also has another cardiovascular effect: It makes platelets, the cells that help blood clot, less clumpy. In other words, the lower your serotonin level, the thicker your blood; and the thicker your blood, the harder it is for the heart to pump.
"People who are depressed have abnormally sticky platelets," says Johns Hopkins professor of medicine Dr. Roy Ziegelstein, who has studied heart disease and mood for more than a decade.
Some researchers suspect that Prozac and other serotonin-boosting drugs might actually help patients with cardiovascular ailments.
The idea has not been studied in humans. But Shively thinks the theory is plausible, and is giving antidepressants to a group of macaques to see whether the medicine can ward off heart disease.
Such research underscores the bond between brain and body. Smith, the McGill professor, says researchers are finding more links between the two.
"The mind and the body are very integrated. There's not really a distinction between the two," she says. "If something goes wrong with the brain, that affects the body. If something goes wrong with the body, that affects the brain."