"We didn't know whether depression, per se, could increase the risk of stroke, but now we have conclusive and compelling evidence that it can," says study researcher An Pan, PhD, research scientist at the Harvard School of Public Health in Boston.
The new findings should serve as a call to action to diagnose and treat depression, experts tell WebMD.
"Depression affects quality of life, heart disease, and stroke risk," says Ralph Sacco, MD. He is chair of neurology at the University of Miami Miller School of Medicine and the immediate past president of the American Heart Association.
"Depression is prevalent and is probably underdetected and undertreated. So this is another reason to think about monitoring people for depression and getting them the proper treatment," he says. Sacco was not involved in the new study.
The new analysis included 28 studies of more than 300,000 people. During a follow-up period that ranged for two to 29 years, there were 8,478 strokes. Depressed people turned out to be 45% more likely to experience any type of stroke than those who were not depressed. They were also at a 55% increased risk for dying from that stroke.
The new findings appear in the Journal of the American Medical Association.
Why Depression Is Linked to Stroke Risk
So how does depression increase stroke risk? There are many theories.
It may be that people who are depressed don't take care of themselves. They tend to eat less healthfully and get less exercise. They may also smoke and engage in other unhealthy behaviors that set them up for strokes.
People who are depressed are also less likely to take their medication as prescribed. This may include blood pressure or cholesterol-lowering drugs. Both high blood pressure and high cholesterol levels are risk factors for stroke.
There are a few other possibilities as well. The same inflammation markers in the bloodstream that set the stage for stroke may also play a role in causing depression. What's more, antidepressants have been linked to stroke risk, too.
Those people who took antidepressants in the new study were more likely to have a stroke than those who were not taking medication to treat their depression. This doesn't mean that the drugs cause strokes. It may be that people who take medication have more severe depression.
"People with depressive disorders or symptoms are more likely to develop a stroke over the course of their lives," says Jeffrey M. Lyness, MD. He is a professor of psychiatry at the University of Rochester Medical Center.
"Depression could be both chicken and egg," he says in an email. "Just because one precedes the other does not necessarily mean that one causes the other."
Depression and stroke are associated with other conditions, including diabetes and high blood pressure. "It might be that the true 'egg' that underlies both depression and stroke for some patients are those other conditions," Lyness says.