Studies Try to Tease Apart the Links Between Depression and Heart Disease

By NICHOLAS BAKALAR
17 dec 2008--People who are depressed are literally sick at heart: they have a significantly increased risk for cardiovascular disease, and no one knows exactly why. Now three new studies have tried to explain this, and they arrive at subtly different conclusions.

The first, led by Dr. Mary A. Whooley of the Veterans Affairs Medical Center in San Francisco, studied 1,017 patients with coronary artery disease for an average of more than four years. Although the study found an association of depression with heart disease, when researchers statistically corrected for other medical conditions, disease severity and physical inactivity, the association disappeared.

They concluded with a relatively straightforward explanation: depression leads to physical inactivity, and lack of exercise increases the risk for heart disease. The study appears in the Nov. 26 issue of The Journal of the American Medical Association.

A second study, published Tuesday in The Journal of the American College of Cardiology, provides a different perspective. It included more than 6,500 healthy men and women with an average age of 51. Researchers tested them for depressive symptoms and followed them for an average of more than seven years.

This study, too, found that behavioral issues like smoking and inactivity were the strongest factors in the increased risk for heart disease among people who are depressed or anxious, accounting for 65 percent of the difference in risk. But they also found that depressed people had higher rates of hypertension and higher levels of C-reactive protein, and that these two physiological factors together accounted for about 19 percent of the increased risk. Mark Hamer, a senior researcher at University College London, was the lead author.

While these two studies suggest that the mechanism by which depression exerts its effect is mostly or entirely through poor health behaviors, a third study, in the December issue of The Archives of General Psychiatry, found that something else might be even more important.

This paper, whose senior author was Dr. Brenda Penninx, a professor of psychiatry at VU University in Amsterdam, studied 2,088 well-functioning adults ages 70 to 79. It found no difference in physical activity between those who were depressed and those who were not.

But it did find that depressive symptoms were associated with an increase in visceral fat accumulation — the pot belly that is a known risk factor for cardiovascular illness. This suggests that there is a biological mechanism that links depression with physiological changes independent of how much a person exercises.

To further complicate matters, Dr. Penninx suggested that her physically healthy subjects might have a different kind of depression. “There is now quite a lot of evidence that among heart attack patients, the physical symptoms of depression are more prevalent,” she said, “which suggests that their depression is different from that seen in an otherwise healthy sample.”

For now, Dr. Hamer, of London, offered what might be the last word on the complicated relationship between depression and heart disease.

“It’s really quite difficult to understand,” he said.