Older people who have sleep apnea, which can be marked by heavy snoring, tend to begin experiencing cognitive decline about 10 years earlier than those without the disorder or those who use a breathing machine to treat their apnea, according to a new U.S. study.

Among older people who developed mild cognitive impairment or Alzheimer’s disease, those with untreated obstructed sleep breathing began to experience mental loss at an average age of 77, compared to age 90 for those without breathing problems, the study team found.

“We didn’t find that snoring causes dementia,” said lead author Dr. Ricardo S. Osorio of The Center for Brain Health at NYU School of Medicine in New York.

“We found that in those people that reported that they had sleep apnea, and were not treating it, the age of decline was earlier.”

Sleep-disordered breathing is very common among the elderly, affecting nearly 53 percent of men and more than 26 percent of women, Osorio and his coauthors write in the journal Neurology.

Researchers reviewed the medical histories of almost 2,500 people ages 55 to 90 who were enrolled in a previous Alzheimer’s disease study and reevaluated every six months. Participants self-reported a diagnosis of sleep apnea or obstructive sleep apnea, and whether they used a continuous positive airway pressure (CPAP) machine at night.

People who would go on to have mild cognitive impairment or Alzheimer’s disease tended to first show signs of memory decline years earlier if they had sleep-disordered breathing that was untreated.

Those without sleep-disordered breathing and those with the disorder who used a CPAP machine all began to experience mental decline at the same age.

“Sleep apnea as we understand it, most people think that it only affects males that are obese and snore in middle age, but it is much more common in late life,” Osorio told Reuters Health by phone.

Late-life sleep apnea is under-recognized and under-diagnosed, Osorio said, and these results may help raise awareness, but should not be alarming to most people.

The study did not establish cause and effect, and Alzheimer’s disease itself can cause sleep problems, he said. But if sleep issues do lead to cognitive decline, it could be due to oxygen deprivation or to sleep fragmentation, he said.

“Apneas produce arousals and wake you up, so you don’t get nice restorative sleep,” Osorio said.

The study adds to growing evidence that obstructive sleep apnea is not only “a severe and serious disease associated with cardiovascular morbidity or mortality, but also brain health and neurocognitive health,” said Dr. Timothy I. Morgenthaler, a sleep-disordered breathing expert at the Mayo Clinic in Rochester, Minnesota.

Since sleep apnea is so under-diagnosed, many people in the group who said they did not have it probably did, which could make the true difference in cognitive decline onset even larger, said Morgenthaler, who wasn’t involved in the study.

Loud and frequent snoring, choking or gasping during sleep, finding that sleep is not restorative and daytime fatigue can be signs of sleep apnea, he said.

“You are trying desperately to sleep, and unfortunately are not able to sleep and breathe at the same time,” Morgenthaler told Reuters Health. Adrenaline levels, stress and inflammation increase, he said.

“It’s not surprising that these people have many downstream effects,” he said.

It is also possible that sleep apnea does not itself cause cognitive decline, and that those who pursue treatment and use a CPAP machine tend to live overall healthier lives than people who do not, Osorio said.

Many people find CPAP machines difficult to use and do not stick with them, but CPAP is not the only treatment option, Osorio said.

“If your partner tells you you snore, then you should maybe talk to your physician,” he said, noting that it is much easier to diagnose sleep apnea today than it once was.

When a patient comes to the doctor’s office with memory complaints, sleep apnea should be one of the diagnoses considered, he added.