People who have been diagnosed with sleep apnea or have trouble sleeping deeply may be at more risk of developing dementia, a new study suggests.
The study, published Wednesday in the journal Neurology, found that people who have reduced oxygen in their blood during sleep— a sign of sleep apnea and other conditions such as emphysema— are more likely to have abnormalities in their brain tissue. The abnormalities, called micro-infracts, are associated with the development of dementia.
In addition, 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 a key indicator of Alzheimer’s disease and dementia, the researchers note. Slow wave sleep is also important in processing new memories and remembering facts. People tend to spend less time in slow wave sleep as they age.
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, and other brain abnormalities associated with Alzheimer’s disease and Lewy body dementia.
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 percent of their time or less with low oxygen levels and the highest group spending 72 to 99 percent 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.
Previous studies have also shown a link between sleep stages and dementia. For this study, the participants were again divided into four groups based on the percentage of the night spent in slow wave sleep. 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 results remained the same after adjusting for factors such as smoking and body mass index and after excluding participants who had died early in the follow-up period and those who had low scores on cognitive tests at the beginning of the study.
“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 Dr. Rebecca P. Gelber, MD, DrPH, of the VA Pacific Islands Health Care System and the Pacific Health Research and Education Institute in Honolulu, Hawaii. “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.”
Gelber noted that a previous study showed that use of a continuous positive airway pressure machine (CPAP) — a form of treatment for obstructive sleep apnea — may improve cognition, even after dementia has developed.
According to the National Heart, Lung, and Blood Institute (NHLBI), sleep plays a vital role in keeping physically healthy, with sleep deficiency associated with increased risks of heart disease, kidney disease, hypertension, diabetes, stroke and obesity. Sleep is also involved in healing, growth, hormonal balance and maintaining a strong immune system.