People with insomnia face a 27 to 45 percent higher risk of heart attack, says a new Norwegian study.
About one-third of people report having trouble sleeping and should see a doctor for help, urged the authors of the study published in Circulation, a journal of the American Heart Association.
"Sleep problems are common and fairly easy to treat," said Lars Erik Laugsand, lead researcher 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 heart attack and talk to their doctor if they're having symptoms."
The data came from 52,610 Norwegian adults who answered a national survey about their insomnia symptoms in 1995-97.
Over the next 11 years, researchers identified 2,368 people who had their first heart attacks, via hospital records and Norway's National Cause of Death Registry.
After adjusting for factors such as age, sex, marital status, education level, blood pressure, cholesterol, diabetes, weight, exercise, shift work, depression and anxiety, researchers found the highest boost in risk among the most troubled sleepers.
When they compared data from people who said they usually slept fine to people who said they had trouble falling asleep almost daily over the course of the last month, they saw a 45 percent higher risk in the sleepless group.
Those who said they could fall asleep but not stay asleep all night showed a 30 percent higher risk of heart attack than the group that slept well.
And those who said they did not wake up feeling refreshed showed a 27 percent higher risk.
The researchers did not adjust their data for obstructive sleep apnea, a condition that arises when air flow is interrupted during sleep, and cautioned that particular sleep patterns among the Norwegian sample may not make the data immediately applicable to other populations.
However, similar links between insomnia and cardiovascular disease have been suggested in previous studies on US populations.
"It is becoming increasingly evident that insomnia is a significant modifiable risk factor for cardiovascular disease," said Girardin Jean-Louis, an associate professor in the Department of Medicine at SUNY Downstate Medical Center, who was not involved in the study.
Jean-Louis said more research was needed, but noted that some sleep conditions like short sleep and obstructive sleep apnea bear two of the same biomarkers as cardiovascular disease -- C-reactive protein and interleukin-6 -- which are proteins linked to inflammation.
The body's regulatory cycle for sleeping and wakefulness, known as circadian rhythms, could also play a role, according to Edward Fisher, professor of cardiovascular medicine at New York University.
"It is known that animals with disrupted circadian rhythms develop metabolic changes that, if they occurred in people, would increase heart disease risk," said Fisher, who also was not a part of the study.
"Overall, independent of the exact mechanism, the association shown seems plausible, and is yet another reason to do as the authors advise -- seek professional help for better sleep," he added.
"Besides improving the general quality of life, it might even provide cardiovascular benefits."