During the first three months after a stroke, survivors are about eight times more likely to experience depression than their peers who didn't experience a stroke, a large Danish study suggests.

Researchers analyzed data on a large group of stroke patients and compared them to similar people who didn't have a stroke.

Within two years after a stroke, 25 percent of patients had a diagnosis of depression, with more than half the diagnoses coming within the first three months.

By comparison, slightly less than 8 percent of the people who didn't have a stroke had a depression diagnosis during the study, and less than a quarter of these cases were found within the first three months of the study.

"The frequency of depression in stroke patients is also much higher as compared to patients experiencing other acute somatic events such as a heart attack," said senior study author Dr. Merete Osler of Copenhagen University in Denmark.

"It seems that some imbalance in the brain induced by the stroke may cause stroke patients to be more susceptible to depression," Osler added by email.

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More than 30 million people worldwide live with a stroke diagnosis, Osler and colleagues note in JAMA Psychiatry.

Depression afterward is common.

As in people who don't have a stroke, the risk for depression increases with age and is also greater for women, individuals who live alone or have less education, and people with diabetes or a history of mental health problems, the authors point out.

To see how stroke may influence the risk of depression, researchers examined data from seven Danish nationwide registries on 157,243 people aged 15 and older hospitalized for the first time with a stroke from 2001 to 2011, and 160,236 similar people without stroke.

Overall, more than 34,000 stroke survivors and more than 11,000 people who didn't have a stroke were diagnosed with depression during two years of follow-up.

Researchers also looked at how depression influenced survival.

For people without a stroke, depression was associated with nearly three-times higher odds of death from any cause during the study period. For stroke survivors, depression was linked to an 89 percent greater likelihood of death during the study.

The heightened death risk was most pronounced with recent onset depression, the study also found.

One limitation of the study, however, is that a depression diagnosis was often identified based on patients filling prescriptions for antidepressants, the authors note. This might not reflect all cases of depression or capture the severity of the condition.

Even so, the findings suggest that doctors, patients and families need to be alert for depression and other mood disorders after a stroke, Dr. Craig Anderson, executive director of the George Institute for Global Health at the University of Sydney, Australia, wrote in an accompanying editorial.

"We know that it is very common - one in three stroke survivors suffer from some form of depression - and that it adversely impacts on recovery and increases the risks of recurrent stroke and other serious cardiovascular events and death," Anderson said by email.

"We know it is difficult to diagnose because patients have problems with speech and memory, and their physical disability, and there is uncertainty how to best manage the condition," Anderson added.

Often, doctors may take a watchful waiting approach for a few weeks after depression symptoms first surface, followed by psychological counseling or antidepressants, Anderson said.

Patients and families should speak up if they suspect a mental health issue.

"Depression is common and it is ok to feel flat and down after a stroke," Anderson said. "However, sometimes this can be more serious and require treatment."