Fifty percent of people with type 2 diabetes and up to 86% of those who are obese may have obstructive sleep apnea (OSA) – breathing pauses during sleep that worsen insulin resistance and boost risk for high blood pressure and heart attacks.
But in new research from Australia’s Baker IDI Heart and Diabetes Institute, the gold-standard treatment for OSA did not improve blood sugar.
The study, published online February 29, 2016 by the American Thoracic Society's American Journal of Respiratory and Critical Care Medicine, tracked 298 women and men with fairly well-controlled type 2 diabetes and newly-diagnosed OSA. Half received CPAPs—continuous positive air pressure devices that gently blow air through a face mask to keep airways open during sleep. The other half did not. When researchers checked everyone’s A1c levels 3 months and 6 months later, they found no differences between the two groups. But CPAP users did get two benefits: Less daytime sleepiness and a 3.5-point drop in their diastolic blood pressure (the bottom number in a blood pressure reading, when the heart is resting between beats.)
"Many studies have indicated that OSA may contribute towards the development and progression of type 2 diabetes," says lead study author Jonathan Shaw, MD, associate professor and head of population health at Melbourne's Baker IDI Heart and Diabetes Institute. “Our study confirmed many of the established benefits of CPAP, so CPAP remains of value to people with diabetes. However, since we saw no benefit for glucose control, trying to improve glucose control is not a reason on its own to use CPAP or to screen for unrecognized OSA [in people with type 2].”
But another study in the same journal, published online February 24, did find better blood sugar for CPAP users under slightly different circumstances. Researchers from Spain’s Hospital Universitario La Paz in Madrid tracked the A1cs of 50 type 2s with a new diagnosis of OSA for six months; half got CPAPs and half just got advice on good sleep habits and a healthy diet.
But compared to volunteers in the Australian study, these volunteers had worse blood sugar levels at the start—their mean A1c level was 7.6%, compared to 7.3% in the Australian study—and more severe OSA, with about 32 breathing pauses per hour during sleep compared to 20 per hour in Shaw’s study. And the CPAP users kept their masks on longer at night – using their devices for an average of 5.2 hours versus 4.9 in the Australian study.
After 6 months, the CPAP group in the Spanish study saw their A1c readings fall by .4%. This was enough to reduce risk for heart attacks by 6 to 8%, and for diabetes-related kidney, vision and nerve problems by 15%, the researchers say.
There may be a tipping point for blood-sugar benefits, says sleep disorders expert Babak Mokhlesi , MD, a pulmonologist and director of the Sleep Disorders Center at the University of Chicago.
Dr. Mokhlesi researches OSA in type 2s, but was not involved with either study. “If you don’t use your CPAP for the entire duration of the night, you may not get all the benefit,” he notes. “People who use their CPAP for just part of the night tend to take it off partway through and so aren’t protected during REM sleep, the sleep stage when we dream and when apnea tends to get worse. There’s more shallow breathing, more pauses in breathing and oxygen levels in the blood drop more dramatically. This may affect blood sugar.”
In a 2014 study of 115 people with type 2 and OSA that was published in the journal Diabetes Care, Dr. Moklhesi’s group found that those whose apnea was worst during REM sleep had A1cs of about 7.3% -- compared to 6.3% in those with the mildest apnea during dream stages of sleep. The researchers estimated that using a CPAP for four hours a night would miss 60% of this time, but wearing one for seven hours would cover 85% of it – and could potentially reduce A1c levels by as much as 1%, a significant improvement.
Dr. Shaw agrees that people with poorer blood glucose control, worse sleep apnea and who wear their CPAP masks longer at night might get blood-sugar benefits. But in any case, people with diabetes who have OSA should use a CPAP for other reasons. “Our study confirmed many of the established benefits of CPAP, so CPAP remains of value to people with diabetes,” he notes.