The dangers associated with night-time breathing disturbances, such as obstructive sleep apnea, are well known: increased risk of high blood pressure, heart attack, stroke and diabetes, not to mention sometimes dangerous daytime drowsiness, according to the National Heart, Lung and Blood Institute.

Now a study suggests that such sleep conditions can hasten the onset of both Alzheimer's disease and "moderate cognitive impairment," such as memory loss, by quite a few years. But in a bit of good news, it concludes that using a continuous positive airway pressure (CPAP) machine, the treatment of choice for sleep apnea, can prevent or delay cognitive problems.

A team of researchers led by Ricardo Osorio, an assistant professor of psychiatry at NYU Langone Medical Center determined that the sleep disturbances brought on mild cognitive impairment at least 11 years earlier in groups of people enrolled in a long-term Alzheimer's disease study, even when they controlled for other factors. In the largest group, that meant self-reported or family-reported cognitive problems, such as memory loss, at about 72 instead of 83.

The same was true for Alzheimer's disease itself, which started in one group at a little older than 83, instead of about 88, when other factors were ruled out. The study was published online in the journal Neurology.

It could be that the intermittent cutoff of oxygen to the brain is responsible for the problems, or the sleep disruption itself may be affecting cognition, Osorio said. Studies are underway to determine the cause.

Obstructive sleep apnea, a condition in which airways are blocked for seconds or minutes during sleep, remains sharply under-diagnosed, especially in older people. The American Sleep Apnea Association estimates that 22 million people have it, and that 80 percent of moderate and severe cases are undiagnosed.

Osorio's study says 52.6 percent of older men and 26.3 percent of older women have it, but most don't know it. This is because doctors and health-care providers don't tend to ask the elderly about apnea and because a higher proportion of them sleep alone, so there is often no one to witness the loud snoring or gasping that accompany apnea.

Previous studies have suggested a link between sleep apnea and an increased risk of Alzheimer's disease, but none had gone so far as estimating how much sooner the dreaded form of dementia might occur. Nor had anyone shown that CPAP devices could mitigate the risks, Osorio said.

The study was conducted by examining the characteristics of people with both normal and abnormal cognitive functioning enrolled in the Alzheimer's Disease Neuroimaging Initiative. The group using the breathing machines, which pump a continuous stream of air through a mask to keep airways open, was small, so Osorio already has begun a pilot study to directly observe whether the CPAP devices delay the onset of cognitive problems.

He said that increased awareness of sleep apnea among older people, in both the general population and among health-care providers, is critical.