Because of combining the conclusion of 17 studies on depression and stroke, researchers discovered that people who suffered depression at one point in their lives were third times more likely to experience stroke in the future compared to the people who never got depressed in their entire lives.

According to Maria Glymour, a professor at the Harvard School of Public Health, the analysis looks decidedly convincing.

However, it is not clear if depression causes the risk of the increased risk of stroke. The study does not also tell if the two diseases have the same underlying causes.

An earlier study by Glymour and her colleagues got integrated in the latest research, led by Dr. Li-Qiang Qin at Soochow University in China.

Qin’s group collected data from 17 studies, which have a total of over 200,000 participants. The research looked at whether people with depression were more likely to suffer a stroke compared to people who did not have symptoms of the mood disorder.

All of the studies started with people who never experience a stroke before, and followed them for anywhere from three to 29 years.

Two studies give details about the depression that got tied to a lower risk of stroke, and another two found just about no difference in risk between those with depression and those without.

The other 13 studies demonstrated an increased risk of stroke for people who shad suffer from depression. As the team combines the result of all the 17 studies, they discovered that the risk of stroke was 34 percent higher among those with depression.

Stroke is considered as the third-leading causes of death in the United States. Some 800,000 Americans — or 26 out of every 10,000 – endure a stroke yearly, based on the records of Centers for Disease Control and Prevention.

A 34 percent rise in the number of strokes would heighten the count to 35 out of every 10,000 people.

A study conducted at an earlier time this year, which pooled the outcomes of 28 research projects on stroke and depression, also discovered an increased risk of stroke among people who had depression problem before, (see Reuters Health story of September 21, 2011).

Neither study determined whether one disease causes the other, and Glymour guesses that the connection between stroke and depression has something to do with unhealthy behaviors.

The study authors also note the association of depression with other diseases development such as diabetes and hypertension, also considered as risk factors for stroke.