More than 25 million Americans have obstructive sleep apnea, a dangerous disorder that causes sufferers to briefly stop breathing while they sleep, sometimes many times each night.

The condition, caused by throat muscles that relax and block the airway, has been linked to heart disease, high blood pressure, strokes and Type 2 diabetes.

The standard treatment, the continuous positive airway pressure, or CPAP, machine, keeps the airway open by pumping a stream of air through a patient’s nostrils as he or she sleeps.

The biggest problem with the therapy is noncompliance; many people find the air mask and hose uncomfortable and give up on the machine.

But a large new sleep study published Sunday raises a serious new issue.

It found that for people with existing cardiovascular disease and moderate to severe sleep apnea, CPAP doesn’t prevent heart attacks, strokes, hospitalizations or deaths any better than sleeping without the machine.

The finding surprised scientists from two Australian research institutes who conducted the research, because previous examinations have shown that CPAP seemed to have a positive impact on those problems.

The study was by far the largest to look into obstructive sleep apnea. It involved 2,687 subjects between the ages of 45 and 75.