BY REBECCA HISCOTT
Disordered breathing during sleep and a shorter duration of slow-wave sleep, or deep sleep, have been linked to dementia-related brain lesions in a new study published in the December 10 online issue of Neurology. People with sleep apnea are especially vulnerable to these brain abnormalities, as are those with conditions like pulmonary hypertension and emphysema, which can cause nocturnal hypoxia — a dangerous dip in blood oxygen levels during sleep, the authors noted.
The investigators pulled data from the Honolulu-Asia Aging Study, a prospective cohort study of Japanese-American men in Honolulu. They examined the records of 167 men who underwent polysomnography around age 84, died an average of six years later, and were autopsied. Sleep tests included measurements of blood oxygen saturation, duration of apnea or hypopnea (shallow breathing during sleep), duration of hypoxemia, and duration of slow-wave sleep. The researchers divided participants into quartiles based on the percentage of time they spent with lower than average blood oxygen saturation during sleep, as well as the time they spent in slow-wave sleep. In a postmortem analysis, they looked for evidence of micro-infarcts, neuronal loss, brain atrophy, neuritic plaques, neurofibrillary tangles, and Lewy bodies.
Obstructive sleep apnea is a recurrent interruption in breathing during sleep. It results from sleep-related muscle relaxation in the upper airway, which leads to a decrease or complete blockage of airflow for brief periods. The blood oxygen level may fall, causing arousals or awakenings that disturb sleep.
The researchers found that participants who had lower blood oxygen levels during sleep were four times as likely to have micro-infarcts, which have been linked to vascular dementia in past research, than those who had more oxygen in the blood. The findings suggest that hypoxia may be the main reason why obstructive sleep apnea can affect cognition, they wrote.
Likewise, participants who spent less time in slow-wave sleep were more likely to have brain atrophy and neuronal loss — which have also been associated with dementia — than those who spent more time in deep sleep. Those who spent more time in short-wave sleep also had less cognitive decline over time, suggesting that short-wave sleep “may protect against cognitive decline, possibly through a reduction in brain atrophy,” the authors wrote.
However, they found no association between blood oxygen saturation or short-wave sleep duration and the hallmark plaques and tangles of Alzheimer’s disease.
“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,” study author Rebecca P. Gelber, MD, MPH, an internal medicine physician with the VA Pacific Islands Health Care System and the Pacific Health Research and Education Institute in Honolulu, said in a news release. She added, “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.”
For patients with sleep apnea, past research has shown that using a continuous positive airway pressure (CPAP) machine can improve cognition, even after dementia has developed, Dr. Gelber added.
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