"This study tells us that if you have a high depression screening score, you have more than a two-fold increase in risk of stroke," said AHA spokesperson Dr. Philip Gorelick, medical director of Mercy Health in Grand Rapids, Michigan. "Furthermore, in the follow up period, if the depression symptoms resolve, you still have 66% risk of having a stroke."
The study was conducted by a group of public health researchers at Harvard, University of California San Francisco, the University of Washington and University of Minnesota, who looked at data from over 16,000 people age 50 and older gathered over a dozen years for the Health and Retirement study
. Every two years between 1998 and 2010, people were quizzed about their depressive symptoms, their stroke history and their behaviors that might put them at risk for stroke.
"We already knew that people with depression, or even symptoms of depression, had higher stroke risk," said lead author Paola Gilsanz. "What we didn't know is whether if the symptoms of depression went away, the stroke risk would also go away."
"We were surprised that for this group of people, with symptoms of depression at one interview but not the second interview, stroke risk remained significantly elevated (by about 66%) compared to people who had not had symptoms of depression at either interview," said co-author Maria Glymour. "We expected the stroke risk would be back to baseline."
Researchers aren't sure why the risk doesn't diminish. Depression is known to be related to unhealthy behaviors that increase cardiovascular risk, such as physical inactivity and smoking, but Glymour doesn't believe these fully explain their findings.
"Another set of possible pathways are biological changes including increased platelet activity, inflammation and cardiometabolic conditions such as hypertension, hyperlipidemia and diabetes," said Glymour.
Gorelick told CNN he isn't surprised by the findings. "I think the depression may have been going on for longer than we realize, so the risk factors have been taking hold over a period of time," he said. "So I'm not surprised that even after symptoms of depression are remitting, there is still a risk. It makes sense to me."
Gorelick said he's glad to see the focus on the connection between cardiovascular risk and depression, and hopes the message gets out to the medical community.
"A lot of practitioners are really not aware of this relationship," said Gorelick. "If you have a patient who is depressed, you'd better be careful, because the depression is going to be a marker that your patient is going to be at risk for stroke and heart attack."
"In some more advanced medical practices," said Gorelick, "what we are now doing is screening for depression, and if you have depression and another cardiovascular risk factor, then these patients are getting very intensive risk management from a team, and the team is now including psychiatrists."
Glymour agrees with the need for action. "Because this is the first study to look at changes in depressive symptoms in this way, we need replication of findings in independent samples and with people of different age groups," she said. "The surprising results make such replications even more urgent."