Low oxygen saturation during sleep and reduced duration of slow-wave sleep both correlate with more pathological features of dementia in the brain, a new study shows. The study, published online Dec. 10 in the journal Neurology, showed that older men with lower oxygen saturation during sleep had more microscopic infarct foci in the brain, a major lesion in vascular dementia, while those with less slow-wave sleep were found to have more brain atrophy at autopsy. In addition, the researchers noted that men with higher levels of slow-wave sleep had less decline in cognitive scores during follow-up, suggesting that this type of sleep may prevent cognitive decline by reducing brain atrophy. Study lead author Rebecca P. Gelber, PhD, of the Department of Veterans Affairs Pacific Islands Health Care System in Honolulu, Hawaii, told Medscape Medical News, “Getting a good night’s sleep is more beneficial than we thought. It may prevent dementia.” She believes doctors must be aware of how people’s sleep affects brain function. “If patients have diseases that cause decreased oxygenation and action such as COPD [chronic obstructive pulmonary disease] or heart failure, they may have a smaller threshold for memory impairment. This is another reason to support interventions for sleep apnea and keeping oxygen levels higher.” Dr. Gelber says slow-wave sleep is more difficult to vary. She added, “But it appears to play a restorative role in brain function and may slow the process that leads to widespread brain atrophy. In terms of predictors of slow-wave sleep, we need to bet on more research.” Getting a good night’s sleep In the current study, Dr. Gelber and his colleagues analyzed data from 167 older Japanese-American men (mean age, 84 years) who underwent sleep studies in their own homes between 1999 – 2000 as part of the Honolulu-Asia Study of Aging and postmortem examinations before 2010. They focused specifically on sleep characteristics measured by a multifunctional sleep recorder and whether these characteristics correlated with brain lesions at autopsy. Participants with oxygen saturation levels below 95 percent had more microinfarcts. Specifically, when sleep time was divided into quartiles based on oxygen saturation levels below 95%, participants in the highest quartile (with the longest time in hypoxia) had almost four times more microinfarcts than those in the lowest quartile (dominance ratio [OR], 3.88; 95% confidence interval [CI], 1.10 – 13.76). Higher oxygen saturation in REM sleep was also associated with less glial cell hyperplasia and blue spot neuron loss. Comparing again the percentage of slow-wave sleep in the highest versus lowest quartile participants revealed that the longer the duration of slow-wave sleep the less brain atrophy (adjusted OR, 0.32; 95% confidence interval, 0.10 – 1.03). The longer the duration of slow-wave sleep, the less cognitive decline Regular cognitive assessments using the 100-point Cognitive Ability Screening Instrument (CASI) showed less cognitive score decline in men with longer duration of slow-wave sleep. The authors noted, “After correcting for potential confounders and excluding participants who died early in follow-up and those with lower baseline cognitive scores, the observed correlations remained consistent, supporting the reasoning that sleep characteristics may precede lesion development.” Puzzlingly, low oxygen saturation during sleep was associated with fewer Louis microsomes at autopsy. The researchers said, “This finding is unexpected and requires continued research.” The current study did not find a correlation between sleep characteristics and Alzheimer’s disease lesions, but Dr. Gelber and his colleagues point to other studies that have shown a correlation between sleep quality and Alzheimer’s disease, namely APOE &espilon; allele 4 is associated with obstructive sleep apnea, and sleep apnea-related adverse cognitive effects are more severe in allele carriers. The researchers concluded, “Our findings suggest that hypoxia during sleep and reduced duration of slow-wave sleep may contribute to major pathological changes in potential cognitive decline in older adults.” They added, “Further research is needed on how [slow-wave sleep] repairs brain function and whether preventing nocturnal hypoxia may reduce the risk of cognitive decline.”