New online research published early in the Annals of the American Thoracic Society¸ indicates that those with sleep-disordered breathing and a genetic predisposition to Alzheimer’s disease are at increased risk of declining cognition than those who do not have the genetic susceptibility.
In this study, researchers found that people with the genetic Alzheimer’s indicator, apolipoprotein ε-4 (APOE-ε4) allele, and varying degrees of sleep-disordered breathing, were more likely to suffer from severe cognitive deficits than people who did not have the allele.
APOE helps the brain repair itself after injury. It carries cholesterol, and previous studies have found that people who carry ε4 allele, the other form of this gene, are more likely to develop Alzheimer’s disease. Scientists currently estimate that approximately 20% of the population carries this gene.
Lead author of the study and instructor at Brigham and Women’s Hospital at Harvard, Dr. Dayna A. Johnson, notes that prior studies have been inconclusive in trying to make the connection between sleep-disordered breathing and cognitive decline. She believes this is partially due to the type of tests used. Several indicators for sleep-disordered breathing and cognition were closely investigated in a diverse sample group for this study. Researchers also looked at the APOE-ε4 allele and whether its presence affected sleep-disordered breathing and cognition.
Researchers reviewed and analyzed data from 1752 people with an average age of 68 for this study. All participants were part of the Multi-Ethnic Study of Atherosclerosis (MESA) and underwent an in-home sleep study, completed a series of tests to measure cognitive function, and filled out sleep questionnaires.
Scientists define sleep-disordered breathing as having an apnea-hypopnea index (AHI) of greater than 15. AHI is the number of times a person stops or slows their breathing in an hour. Sleep apnea syndrome has an AHI of greater than 5, with 5 being in the normal range. Additionally, researchers took into consideration the self-reported sleepiness scale.
Findings from this study include the following:
- Increased daytime sleepiness was linked to slower cognitive processing
- Increased hypoxemia throughout the night, with oxygen saturation below 90%, and increased daytime fatigue were associated with poorer memory and attentions span
- Poor attention and processing speed were associated with sleep apnea syndrome
- These links were more prominent in people who carried the APOE-ε4 allele
Findings were adjusted for several factors including education level, smoking status, diabetes, hypertension, race, age, BMI, depressive symptoms, and benzodiazepine use.
While the effects of the measured sleep factors were small in this research, Dr. Johnson notes that they are still in the range reported in prior studies for other health and lifestyle risk factors for dementia. Therefore, findings indicate that early identification and treatment of sleep-disordered breathing may help reduce the risk of Alzheimer’s dementia, especially in people who carry the APOE-ε4 allele.
This research further proves that sleep-disordered breathing negatively affects memory, cognitive processing speed, and attention span, which are predictors of cognitive dysfunction. There is no effective treatment for Alzheimer’s disease, but this research offers the potential for screening and treating sleep-disordered breathing as a strategy to help reduce the risk of dementia.