The researchers also adjusted the data to account for other factors that could contribute to cognitive impairment or dementia, such as age, education, body-mass index, diabetes, smoking, medication use and baseline scores for brain health, according to the study.
They found that 31 percent of women with normal night-time breathing patterns developed cognitive impairment over the study period, compared to 45 percent of the women who had sleep-disordered breathing. That translates to 85 percent higher relative odds of cognitive impairment or dementia for the women with sleep-disordered breathing.
They also found that the cognitive impairment was associated with bouts of oxygen deprivation caused by sleep apnea, but not with fragmented sleep (such as arousal or waking after falling asleep) or sleep duration.
Since sleep-disordered breathing affects up to 60 percent of the elderly, any association between sleep apnea and cognitive impairment -- even a modest one -- could have a major public health impact, the researchers noted.
But whether or not treating sleep-disordered breathing could reduce the risk of dementia or cognitive impairment is the "million dollar question," said Redline. She said other research suggests that several months of sleep apnea therapy may help improve brain function, but that much larger studies with longer treatment periods and a more diverse population need to be done.
"This could be a chicken-and-egg problem," pointed out geriatric psychiatrist Dr. Gary Kennedy from Montefiore Medical Center in New York City. While it may be that sleep-disordered breathing contributes to cognitive impairment or dementia,
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