THURSDAY, Nov. 15, 2007 (HealthDay News) -- Depression is known to hike the risk of cardiovascular disease, but don't put all the blame on any concurrent rise in inflammation.
So concludes a study led by Dr. Viola Vaccarino, a professor of medicine at Emory University, in Atlanta.
That means that it's back to the drawing board in terms of unraveling the depression-heart disease link, according to Vaccarino.
"That depression is a factor in cardiovascular disease is clear. What is not clear is what kind of mechanism is involved," she said.
The Emory group, as well as researchers from five other medical institutions, studied the possible role of inflammation in a group of 559 women who were referred for heart tests because of blockage in a coronary artery. All the women had a standard test for depression at the start of the study and were followed for an average of about six years.
They were divided into three groups on the basis of those tests: those who clearly were depressed by diagnosis and previous treatment; those who might be depressed because of either a diagnosis or treatment; and those who had no indicator of depression.
The researchers made frequent measurements of two molecules linked to the inflammatory response -- C-reactive protein (CRP) and interleukin-6.
There were 79 major events of cardiovascular disease during the study, 23 of them fatal.
As expected, the incidence of such events was 2.5 times higher in women with depression. There was no comparable increase in women classified as possibly depressed.
The team found that women diagnosed as depressed had a 70 percent higher level of C-reactive protein and a 25 percent higher level of interleukin-6 compared to women who were not depressed. Women classified as possibly depressed had elevated levels of both markers, but to a lesser extent.
The bottom line, according to the researchers, was that while inflammation was tied to heart risk, it failed to explain most of the cardiovascular danger posed by depression.
"Despite being associated with each other, depression and inflammation predicted future events for the large part independently," the researchers wrote. "Thus, despite a clear relationship between depression and inflammation, the latter plays only a minor role in the higher risk of adverse outcomes for women with depression."
The finding is something of as surprise, said Dr. David S. Sheps, professor of medicine at the University of Florida at Gainesville, a member of the research team.
"We know from other studies that there is a relationship between depression and elevation of certain inflammatory molecules, but no one knows for sure what the mechanism is," Sheps said.
"What is clear is that inflammation does not play a substantial role," Vaccarino said. "We need to look at other things. Perhaps there is a change in the ability of platelets to aggregate." Platelets are blood cells that can form clots to block arteries. "And there could be other pathways," she said.
There's more on C-reactive protein and heart disease at the American Heart Association.