updated 8/10/2011 12:49:23 PM ET 2011-08-10T16:49:23

Elderly women who have sleep apnea, a condition in which breathing is disrupted during sleep, are about twice as likely to develop dementia within the next five years as those without the condition, according to a new study.

In the study of 298 women over age 65, the researchers found that 44.8 percent of women with sleep apnea developed dementia or mild cognitive impairment, while 31.1 percent of those who didn't have sleep apnea did.

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The study "suggests that there is a biological connection between sleep and cognition and also suggests that treatment of sleep apnea might help prevent or delay the onset of dementia in older adults," said study researcher Dr. Kristine Yaffe, a professor of psychiatry, neurology and epidemiology at the University of California, San Francisco.

The findings showed that sleep apnea, also known as sleep-disordered breathing, can deprive the brain and other organs of the oxygen and might, over time, trigger declines in cognitive ability, the researchers said.

"While we cannot conclude from these results that [apnea] causes cognitive impairment, our study suggests that it may at least be a contributing factor," Yaffe said.

Why breathing stops

In people with sleep apnea, the airways leading from the lungs to the nose and mouth collapse during sleep, interfering with the ability to inhale. People with sleep apnea usually snore, and they wake up many times each night for very brief periods as they gasp for air.

Previous research had found an association between sleep apnea and dementia, but in the new study, the women participating were tested to ensure they did not have dementia or cognitive impairments at the study's start, the researchers said.

Sleep specialists went to the study participants' homes and monitored the women as they slept using equipment that measured brain activity, airflow, breathing and the oxygen content of their blood, among other measures. The women also took tests that measured their cognitive abilities, memory and verbal fluency.

About one-third of all the women developed dementia or mild cognitive impairment, the researchers said. Those with sleep apnea were almost twice as likely to become cognitively impaired.

Oxygen and dementia

The findings suggest that the key factor leading to diminished cognition was oxygen deprivation, also known as hypoxia, the researchers said. Women who had frequent episodes of low oxygen or spent a large portion of their sleep time in a state of hypoxia were more likely to develop cognitive impairment.

In contrast, no connection was seen between dementia and the number of times patients were awakened in their struggle to breathe, the study said.

Some previous studies have suggested that providing oxygen to patients with Alzheimer's disease and sleep apnea slows their cognitive decline, the researchers said.

The new findings suggest that giving oxygen to elderly people with sleep apnea may reduce their chances of becoming cognitively impaired or could delay the onset of mental decline, the researchers said.

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The findings were published today (Aug. 10) in the Journal of the American Medical Association.

Pass it on: Those whose breathing is disrupted during sleep may be more likely to develop dementia.

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