Common Sleep Problem Raises Dementia Risk

Sleep-disordered breathing, or sleep apnea, is a common condition characterized by repeated awakenings and pauses in breathing during the night. People with the disorder often snore and gasp during sleep, and it has been associated with hypertension, cardiovascular disease and diabetes. Now a new study suggests it may also be associated with mental decline and dementia.

The study, published in The Journal of the American Medical Association, is not the first to find a connection between sleep apnea and dementia, but it is the first to use an objective measure of sleep-disordered breathing — actually counting the number of disordered breathing events during a night of sleep using EEGs and other equipment. It is also the first to study the matter prospectively, first finding the disordered sleeping pattern in healthy people without dementia, and then checking, years later, to see if they were more likely than regular sleepers to deteriorate mentally.

The scientists, led by Dr. Kristine Yaffe, a professor of psychiatry at the University of California, San Francisco, studied 298 physically and mentally healthy women, average age 82. They were recruited from four geographic areas: Baltimore County in Maryland; Minneapolis; Portland, Ore.; and the Monongahela Valley near Pittsburgh.

Each woman completed a battery of tests of mental acuity and spent a night attached to devices to measure breathing and wake-sleep patterns. Of the 298 women, 105 met the criteria for sleep-disordered breathing, with an average of 15 or more episodes of interrupted breathing per hour during the night.

At a re-examination five years later, 45 percent of the women with sleep-disordered breathing had developed mild cognitive impairment or dementia, compared with 31 percent of those who slept normally. After controlling for age, race, body mass index, education level, smoking status, the presence of diabetes or hypertension, and the use of antidepressants and other medicines, the women with sleep-disordered breathing at the start of the study were 85 percent more likely to have mild cognitive impairment or dementia after five years than those whose nighttime breathing was normal.

Sleep itself plays a role in the consolidation of long-term memory, so the scientists at first suspected that the frequent interruptions of sleep, and getting less sleep, might have caused the effect. But they found that the number of sleep disruptions and the total duration of sleep had no association with mental impairment. It was only hypoxia — reduced oxygen to the brain caused by the breathing disruptions — that was consistently associated with mental impairment.

The authors acknowledge that their study has certain limitations. Sleep data was gathered for only one night, so possible variability in sleep disturbances over time was not captured. And the study involved mostly white women, so the results may not be generalizable to men or to people of other races and ethnicities. But the prospective design and the objective measures of sleep-disordered breathing give the study considerable strength.

“I don’t think everyone should be running to a sleep lab,” Dr. Yaffe said, “but if you have sleep apnea you probably want to be monitored for cognitive symptoms. And this may be another reason to be evaluated for sleep problems. There are studies that suggest that if you treat sleep apnea you actually may improve cognitive ability.”

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