Severe sleep apnea raises the risk of dying early by 46 per cent, US researchers have reported, but said people with milder sleep-breathing problems do not share that risk.

They said people with severe breathing disorders during sleep were more likely to die from a variety of causes than similar people without such sleep disorders. The risks are most obvious in men aged 40 to 70, Naresh Punjabi of Johns Hopkins University in Baltimore and colleagues found.

Sleep apnea is caused by a collapse of the upper airway during sleep. Strong snoring can be a symptom but what makes apnea different are numerous brief interruptions in breathing.

Sleep apnea is closely linked with obesity, high blood pressure, heart failure and stroke, but researchers have not been able to clearly quantify how much more likely it makes a person to die.

Punjabi's team studied 6,400 men and women for an average of eight years. Those who started with major sleep apnea were 46 per cent more likely to die from any cause, regardless of age, sex, race, weight or smoking, they reported in the Public Library of Science journal PLoS Medicine.

Men aged 40 to 70 with severe sleep-disordered breathing were twice as likely to die from any cause as healthy men the same age, they reported in a study.

"Among men, 42.9 per cent did not have sleep-disordered breathing, 33.2 per cent had mild disease, 15.7 per cent had moderate disease, and 8.2 per cent had severe disease," they wrote.

They said about 25 per cent of the women had mild sleep apnea, 8 per cent had moderate disease and 3 per cent had severely disordered breathing.

The researchers, funded by the National Heart, Lung, and Blood Institute of the National Institutes of Health, said people with milder sleep-breathing disorders were not more likely to die early.

The NHLBI estimates 12 million adult Americans have sleep apnea, but most are not diagnosed or treated. The National Sleep Foundation puts the number at 18 million.

"In severe sleep apnea a patient's airway is blocked while the patient suffers for 20 to 30 seconds and wakes up.

When it becomes this frequent -- 30 times per hour -- about every two minutes it is severe sleep apnea and can become a problem," said Dr David Rapoport of New York University, who worked on the study.

"The best treatment for sleep apnea is weight loss."

However, the most successful treatment can be a nasal CPAP (continuous positive airway pressure) mask that applies pressure to help keep the airways of a patient open while they sleep, allowing normal breathing," he added in a statement.

"Another possible helpful treatment is surgery. That may include tonsil removal," said Rapoport. "A mouth guard that pulls a patient's mouth forward is another option.”

A small Canadian company, Victhom Human Bionics, has filed a patent on a new device to detect sleep apnea, which must usually be diagnosed in a sleep lab and Medtronic Inc. makes sleep apnea devices. – Reuters