Researchers found people who don't have as much oxygen in their blood during sleep, which occurs with sleep apnea and conditions such as emphysema, are more likely to have tiny abnormalities in brain tissue, called micro infarcts, than people with higher levels of oxygen in the blood.
These abnormalities are associated with the development of dementia, researchers said.

"These findings suggest that low blood oxygen levels and reduced slow wave sleep may contribute to the processes that lead to cognitive decline and dementia," said study author Rebecca P Gelber of the VA Pacific Islands Health Care System and the Pacific Health Research and Education Institute in Honolulu, Hawaii.

People who spent less time in deep sleep, called slow wave sleep, were more likely to have loss of brain cells than people who spent more time in slow wave sleep.

Loss of brain cells is also associated with Alzheimer's disease and dementia.

For the study, 167 Japanese American men had sleep tests conducted in their homes when they were an average age of 84.
All were followed until they died an average of six years later, and autopsies were conducted on their brains to look for micro infarcts, loss of brain cells, the plaques and tangles associated with Alzheimer's disease and Lewy bodies found in Lewy body dementia, reported.

The researchers divided the participants into four groups based on the percentage of time spent with lower than normal blood oxygen levels during sleep, with the lowest group spending 13 per cent of their time or less with low oxygen levels and the highest group spending 72 to 99 per cent of the night with low oxygen levels.
Each group had 41 or 42 men. Of the 41 men in the lowest group, four had micro infarcts in the brain, while 14 of the 42 men in the highest group had the abnormalities, making them nearly four times more likely to have brain damage.     

Of the 37 men who spent the least time in slow wave sleep, 17 had brain cell loss, compared to seven of the 38 men who spent the most time in slow wave sleep.

The study was published in the journal Neurology.

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