Sleep apnea sometimes reduces oxygen levels and can be accompanied by loud snoring. (Canadian Press)

People who snore heavily or have sleep apnea burn more calories when resting when the condition is more severe, researchers have found.

In sleep apnea and other sleep-related breathing disorders, the airways become partially or completely blocked during sleep. Signs include frequent snoring and fatigue during the day. Untreated, sleep apnea can lead to serious health problems, such as an increased risk of heart attack or stroke and accidents.

In the December issue of the Archives of Otolaryngology (head and neck surgery, including ears, nose and throat), Dr. Eric Kezirian of the University of California, San Francisco, and his colleagues measured resting energy expenditure, or the number of calories burned while resting, for 212 adults suspected of having sleep-related breathing disorders.

Obesity is a major risk factor for developing sleep-related breathing problems, and changes in body mass are linked with changes in the severity of sleep-disordered breathing, the researchers noted.

"It is unclear whether weight gain is simply a cause of sleep-disordered breathing or whether sleep-disordered breathing may be associated with alterations in energy metabolism that, in turn, lead to weight gain and complicate the treatment of these two disorders that often coexist," the study's authors wrote.

Resting workout

The researchers found that the average number of calories burned during rest was 1,763 per day. But those who scored the worst on a scale of apnea and disruptions in breathing burned 1,999 calories per day, about 300 more on average than those who scored the lowest.

The difference in calories consumed amounts to a vigorous 30-minute workout at the gym for someone who weighs 155 pounds, according to the Harvard Heart Letter.

Responses of the nervous system may affect the number of calories burned during rest, or energy intake, the researchers suggested.

"This study advances our knowledge concerning sleep-disordered breathing and metabolic rates, but it does not define the connection between sleep-disordered breathing and body weight," they said.

For example, heavy snorers and people with sleep apnea may use more energy struggling to breathe during sleep.

The study also did not take into account whether fatigue limits physical activity levels among people with sleep-disordered breathing.