In a study of more than 16,000 average Americans over the age of 50 years, participants who had persistently elevated depressive symptoms for 4 years experienced double the risk of a first-time stroke compared with those who had consistently low depressive symptoms.
Among the 16,178 people who had never had a stroke when they were selected from a nationally representative cohort of around 20,000 Americans (the Health and Retirement Study), there were 1,192 first-time events in the 12 years of the analysis, which took observations of depression symptoms and established stroke risk factors.
For two consecutive interviews across a 4-year period, those people who had answered with a high level of depressive symptoms were more than twice as likely to have a first stroke in the following 2-year period as those who had not reported depression.
Publishing in the Journal of the American Heart Association, the researchers, including lead author Paola Gilsanz, ScD, a Harvard University research fellow, used measures of depression based on yes/no answers given to survey questions about whether there were, in the previous week:
- Feelings of being depressed
- Of everything being an effort
- Sleep problems
- An inability “to get going”
- Feelings of loneliness.
Yes/no answers against whether or not respondents enjoyed life, felt sad, or were happy made up the other three elements of the eight-item depression scale, believed to be an accurate research test for depression.
Dr. Gilsanz, based at Harvard’s T.H. Chan School of Public Health in Boston, MA, says: “Our findings suggest that depression may increase stroke risk over the long term.”
The depression scores were surveyed every 2 years for the 12 years between 1998 and 2010, and the study found that stroke risk remained elevated even among participants whose depressive symptoms went away between interviews – particularly for women.
Dr. Gilsanz talks about the delayed link observed between depression and stroke:
“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.
We were surprised that changes in depressive symptoms seem to take more than 2 years to protect against or elevate stroke risk.”
Another finding of the study was that the stroke link to depression was stronger for when people were under 65 years of age compared with the risk when depression happened during older age.
The authors discuss potential mechanisms that need to be proven to explain the links they have observed between depression and stroke, but are firmer about an idea that the “effects occur over the longer term through accumulated damage” – describing possible short-term effects linked to depression as less likely.
This is because the researchers “saw little differential in stroke risk prediction by short-term increases or decreases in depressive symptoms.”
Maria Glymour, ScD, senior author and an associate professor of epidemiology and biostatistics at the School of Medicine of the University of California, San Francisco, says:
“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.”
On the long-term reasons discussed by the authors that might be potential mechanisms between depression and stroke, they cite links in ‘depressive types’ to various physiological risk factors for stroke that develop slowly over time and “can promote vascular disease and create a substrate for thrombotic or embolic events” (the blood clot forming at the brain site or traveling to it after formation elsewhere).
These longer-term culprits for a potential mechanism include hypertension (high blood pressure), dysregulation of the autonomic nervous system and increased inflammatory responses.
A potential indirect link for stroke from relationships between depression and behavioral risk is also considered by the authors – the lifestyle factors of smoking and physical inactivity that increase the danger of stroke could be more likely in depression.
A study published in the journal Stroke last year also found a link to depression. The rates of full and mini-stroke were compared between people of different psychological profiles and, as we reported in July 2014, an increased risk of stroke was linked to chronic stress, and depressive symptoms in particular.