People are generally most likely to die of a heart attack between 6 a.m. and noon, as the body and its systems wake up, and least likely to succumb to heart attacks between midnight and 6 a.m. But that pattern may not hold true for all people, particularly those who suffer from obstructive sleep apnea, a condition affecting up to a quarter of all American adults, in which a blocked airway causes breathing to stop periodically during sleep. Researchers from the Mayo Clinic looked at the timing of death from heart attacks in people with and without obstructive sleep apnea to see if the time of death differed.

What the researchers wanted to know: Are people with obstructive sleep apnea likely to die from heart attack at a different time than others?

What they did: The researchers looked at the medical records of 112 people who had died suddenly of heart attacks between 1987 and 2003 and had been given a polysomnography—a test to measure sleeping patterns—before they died. Thirty-four of the subjects did not have obstructive sleep apnea, though some had other types of sleep apnea. The researchers compared the time of death of those with obstructive sleep apnea to the time of death of those without. Some of the people in the study had been treated with a common therapy for obstructive sleep apnea, though they were not separately analyzed after the researchers concluded the therapy did not impact the time of their deaths.

What they found: People with obstructive sleep apnea were more likely to die between midnight and 6 a.m. than people without the disorder. Forty-six percent of the subjects with obstructive sleep apnea died of heart attack during that time, as compared with 21 percent of the subjects without it. In the general population, other studies have found that about 16 percent of heart attacks happen between midnight and 6 a.m. People with more severe obstructive sleep apnea were more likely to die during the wee hours of the morning than those with moderate cases.

What it means to you: This study is interesting, especially for clinicians who deal with heart attacks and want to look at their causes. The study does not deal with the overall risk of heart attack in people with obstructive sleep apnea—whether it increases risk is still unknown. (But it does suggest there's some link.) If you do want to treat it there are things that can help, some of them as easy as sleeping on your side rather than your back‑so ask your doctor if you are concerned.

Caveats: Because some of the research subjects died in their sleep, it was hard to tell in some cases how sudden the sudden deaths actually were.

Find out more: The American Sleep Apnea Association has lots of information about sleep apnea, including a comprehensive definition.

Also try the National Heart, Lung, and Blood Institutes page on sleep apnea with definitions and treatment options.

Read the article: Gami, A.S. et al. "Day-Night Pattern of Sudden Death in Obstructive Sleep Apnea." New England Journal of Medicine. March 24, 2005, Vol. 352, No. 12, pp. 1206-1214.

Abstract online: http://content.nejm.org