Sleep apnea, a disorder that can cause sufferers to temporarily stop breathing while snoozing, has long been associated with obesity. Paradoxical new findings suggest an ironic benefit: the worse the disease gets, the more calories patients burn.

"It's something of a silver lining," says Eric Kezirian, director of the division of sleep surgery at the University of California, San Francisco, whose research appears in today's Archives of Otolaryngology-Head & Neck Surgery. "It's not hurting in certain areas, but may be hurting in other areas."

Kezirian measured resting energy expenditure, or how many calories 212 patients with sleep apnea burned when they were awake but not exercising. He extrapolated the five-minute measurement to a full day, concluding that patients with the worst sleep apnea burned 1,999 calories in a day, compared with 1,626 by those with milder forms.

While the overall difference in energy expenditure isn’t huge, cumulatively it may help some patients lose weight, he says. But the downside, Kezirian adds, is that the ramped up metabolism that comes with worse sleep apnea has side effects including high blood pressure, increased risk of stroke and heart attack.

The relationship between sleep apnea and metabolic changes isn’t fully understood. Weight gain may contribute to the disorder, but sleep apnea itself may affect hormones important for metabolism, including leptin (which makes us feel full) and ghrelin (which tells us we're hungry), and may also contribute to insulin resistance, a precursor to diabetes.

Image © iStockphoto/Royce DeGrie