Study reveals that persistent depression may increase stroke risk even after the symptoms of depression go away.

As if depression isn’t serious enough, it’s now linked to stroke.

Research published this week in the Journal of the American Heart Association reveals that persistent depression may double the risk of stroke in adults over 50 years old. Stroke risk also remains higher even after symptoms of depression go away.

The National Institute of Mental Health (NIMH) defines persistent depressive disorder as a depressed mood that lasts for at least two years.

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

“This study adds to a body of literature that shows an association between depressive symptoms and stroke,” Gilsanz said. “What our research adds is evidence that these effects take time to accumulate, but we still have many questions to answer about how and why this happens.”

Gilsanz added that unraveling this mystery will help reduce the link between depression and stroke, so people who recover from depression do not have lingering health effects.

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The researchers used data from 16,178 participants who were 50 years of age and older and who had been interviewed every two years between 1998 and 2010 as part of the Health and Retirement Study, which was supported by the National Institute on Aging and the Social Security Administration.

Participants answered questions about depressive symptoms, history of stroke, and stroke risk factors.

The study documented 1,192 strokes over 12 years and discovered that people with high depressive symptoms at two consecutive interviews were more than twice as likely to have a first stroke compared to people without depression at either interview.

They also found that people who had depressive symptoms at the first interview but not the second had a 66 percent higher stroke risk.

Gilsanz said that evaluating how changes in depressive symptoms over time may be associated with strokes allowed researchers to understand if the risk of stroke increases after elevated depressive symptoms start or if risk goes away when depressive symptoms fade.

“We were surprised to see that people who only recently reported symptoms of depression did not seem to have higher risk of stroke, but people who previously had symptoms of depression, but they later resolved, seemed to remain at higher risk of stroke for at least the next two years,” said Gilsanz. “This suggests that changes in depressive symptoms may take more than two years to influence risk of stroke.”

Researchers did not evaluate whether depressive symptoms diminished because of treatment or for other reasons. However, they said the findings suggest that treatment, even if effective for depression, may not have immediate benefits for stroke risk.

Researchers also suggested that diminished depression may have a stronger effect on women than men. However, recent onset of depression was not associated with higher stroke risk.

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The NIMH reports that nearly 7 percent of adults in the United States experience major depressive disorder in any given year.

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.

Because this is the first study to examine changes in depressive symptoms in this way, Gilsanz says the next step is to examine if these findings remain true in different samples, across different age groups, and with people whose symptoms went away for different reasons.

“The surprising result that people have elevated risk of stroke even when their symptoms of depression get better make such replications even more urgent. In order to be better able to design interventions to prevent depression related strokes, future research should continue to examine the possible biological and behavioral pathways linking the two,” said Gilsanz.

She also points out that some researchers argue that this association is actually due to subclinical vascular disease in the brain causing both depression and stroke.

“Future studies to tease this out, for example incorporating brain imaging or other research designs, may be able to address this concern,” Gilsanz said.

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