Having trouble sleeping? If so, you could have a moderately higher risk of having a myocardial infarction, according to research reported in Circulation: Journal of the American Heart Association.

In a recent study, the risk of myocardial infarction in people with insomnia ranged from 27 percent to 45 percent greater than for people who rarely experienced trouble sleeping.

Researchers related myocardial infarction risks to three major insomnia symptoms. Compared to people who reported never or almost never having these problems, people who:

• Had trouble falling asleep almost daily in the last month had a 45 percent higher myocardial infarction risk;
• Had problems staying asleep almost every night in the last month had a 30 percent higher myocardial infarction risk; and
• Didn't wake up feeling refreshed in the morning more than once a week had a 27 percent higher myocardial infarction risk.

"Sleep problems are common and fairly easy to treat," said Lars Erik Laugsand, M.D., lead researcher and internist from the Norwegian University of Science and Technology Department of Public Health in Trondheim. "So it's important that people are aware of this connection between insomnia and myocardial infarction and talk to their doctor if they're having symptoms."

Myocardial infarction risk also increases with each additional insomnia symptom, researchers said.

The study was based on 52,610 Norwegian adults who answered questions about insomnia as part of a national health survey in 1995-97. Researchers examined hospital records and Norway's National Cause of Death Registry to identify 2,368 people who had first-time myocardial infarctions during the following 11 years.

The researchers used survival analysis to adjust for factors that could influence the results such as age, sex, marital status, education level, blood pressure, cholesterol, diabetes, weight, exercise and shift work. They also considered depression and anxiety, both of which can cause insomnia.

Up to 33 percent of people in the general population experience at least one insomnia symptom, according to researchers. Previous smaller studies have linked insomnia to heart disease, including high blood pressure and myocardial infarctions. Every year, about 785,000 Americans have a first-time myocardial infarction.

It's unclear why insomnia is linked to higher myocardial infarction risk. Some suggest sleep problems affect myocardial infarction risk factors such as high blood pressure and inflammation.

Researchers didn't adjust for obstructive sleep apnea, and results may not apply to worldwide because daylight hours and sleep patterns differ from Norwegians, said Laugsand, noting that further study is needed.

Co-authors are Lars J. Vatten, M.D., Ph.D.; Carl Platou, M.D. and Imre Janszky, M.D., Ph.D. Individual author disclosures are on the manuscript.