Long-term depression may double stroke risk despite treatment

"Our findings suggest that depression may increase stroke risk over the long term," said Paola Gilsanz, Sc.D., study lead author and Yerby Postdoctoral Research Fellow at Harvard University's T.H. Chan School of Public Health in Boston, Mass.

Researchers used data from 16,178 participants (ages 50 and older) who had been interviewed as part of the Health and Retirement Study about depressive symptoms, history of stroke, and stroke risk factors every two years in 1998-2010.

The study documented 1,192 strokes over 12 years. Compared to people without depression at either interview:

• People with high depressive symptoms at two consecutive interviews were more than twice as likely to have a first stroke.
• People who had depressive symptoms at the first interview but not the second had a 66 percent higher stroke risk.

Researchers did not evaluate whether depressive symptoms diminished because of treatment or for other reasons; but findings suggest that treatment, even if effective for depression, may not have immediate benefits for stroke risk. Researchers also suggest that diminished depression may have a stronger effect on women than men. However, recent onset of depression was not associated with higher stroke risk.

"Looking at how changes in depressive symptoms over time may be associated with strokes allowed us to see if the risk of stroke increases after elevated depressive symptoms start or if risk goes away when depressive symptoms do," Gilsanz said. "We were surprised that changes in depressive symptoms seem to take more than two years to protect against or elevate stroke risk."

Previous research has shown that depression is associated with an increased risk of high blood pressure, abnormalities of the autonomic nervous system and increased inflammatory responses. Depression might trigger underlying vascular problems, including infection or atrial fibrillation, and depressed people are also more likely to smoke and be less physically active.

"Although we now know that depression strongly predicts stroke on par with many other major stroke risk factors, we still need research to understand exactly why this link occurs and whether we can potentially reduce stroke risk by treating depression," said Maria Glymour, Sc.D., study senior author and an associate professor of epidemiology and biostatistics at the University of California, San Francisco School of Medicine.