Previous studies have shown a link between sleep stages and mental decline. This is the first to show that certain sleep features are related to brain changes.
Older men with sleep disturbances appear more likely to have brain changes associated with dementia, according to a new study, adding to evidence that poor sleep may play a role in mental decline.
“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 lead author Rebecca P. Gelber, MD, DrPH, of the VA Pacific Islands Health Care System and the Pacific Health Research and Education Institute in Honolulu.
Dr Gelber and colleagues set out to determine how sleep-disordered breathing, nocturnal hypoxia, and changes in sleep architecture in older patients may be related to the development of the neuropathologic correlates of dementia. They conducted a prospective cohort study of 167 Japanese American men, mean age 84 years, in Honolulu who underwent at-home polysomnography in 1999–2000.
All of the men were monitored until they died an average of 6.4 years later. Autopsies were conducted on their brains to look for microinfarcts, loss of brain cells, the plaques and tangles associated with Alzheimer disease, and Lewy bodies found in Lewy body dementia.
Loss of brain cells was more common in men who spent less time in slow wave, or deep, sleep (sleep that is important in processing new memories and remembering facts) than in those who spent more time in slow wave sleep. Persons tend to spend less time in slow wave sleep as they age, the researchers noted. Loss of brain cells also is associated with Alzheimer disease and dementia.
The researchers divided the participants into 4 groups based on the percentage of time spent with lower than normal blood oxygen levels during sleep. The lowest group spent 13% of their time or less with low oxygen levels, and the highest group spent 72% to 99% of the night with low oxygen levels.
Microinfarcts in the brain were seen almost 4 times as frequently in the one-fourth of men with the lowest oxygen levels during sleep than in men who had the highest oxygen levels. There was no association between the sleep measures and the level of plaques and tangles.
The researchers noted that the causes of low oxygen levels during sleep were unclear and that brain changes could have occurred before the sleep tests.
Previous studies also have shown a link between sleep stages and dementia. But this is the first study to show that certain sleep features are related to brain changes, Dr Gelber noted.
“More research is needed to determine how slow wave sleep may play a restorative role in brain function and whether preventing low blood oxygen levels may reduce the risk of dementia,” she said.
Although the study did not actually show that sleep apnea per se is related to brain changes, Dr Gelber noted that a previous study showed that use of a continuous positive airway pressure machine for obstructive sleep apnea may improve cognition, even after dementia has developed.
The researchers published their results on December 10, 2014 in the online issue of Neurology.