Sleep Apnea and Cognitive Decline: Exploring the Impact on Neurodegenerative Diseases
It is estimated that over 30 million people suffer from sleep apnea in the US, with a global incidence of over 1 billion. Obstructive sleep apnea (OSA), the most common form of this sleep health disorder, can significantly affect both physical and mental health, including cognitive health. Sleep apnea is defined by breathing that intermittently starts and stops throughout the night. Obstructive Sleep Apnea (OSA) represents 85% of all sleep apnea cases and is caused by muscles that relax during sleep, resulting in blocked upper airways. People who suffer from sleep apnea have symptoms including excessive daytime fatigue, morning headaches, irritability, and overall “brain fog.” Symptoms of cognitive decline are the subject of emerging research on neurodegenerative diseases and their connection to sleep apnea.
Sleep Apnea and Neurodegenerative Diseases
Neurodegenerative diseases, according to the NIH Institute of Environmental Health Sciences, occur when cells in the brain and tangential nervous system stop functioning over time and eventually die. The two most common neurological diseases are Alzheimer’s and Parkinson’s. The location in the brain that reflects cognitive decline and how the damage spreads are common to both Alzheimer’s and sleep apnea. Mild cognitive impairment, often an early sign of both diseases, has been seen earlier in patients with sleep-disordered breathing. In patients with diagnosed sleep apnea, mild cognitive impairment was found up to 10 years earlier than those without sleep apnea.
Mechanisms and Effects of Sleep Apnea on the Brain
The actual cause of Alzheimer’s disease is believed to be the build-up of proteins in and around brain cells. The particular protein known as beta-amyloid and its associated plaque are hallmarks of damage seen in the brain scans of Alzheimer’s patients. The disrupted, fragmented sleep most associated with sleep apnea has also been associated with a build-up of these proteins and the resulting plaque in the Alzheimer’s brain.
When breathing is disrupted repeatedly throughout the night, blood oxygen levels drop, and blood flow to the brain is reduced. These cycles of intermittent hypoxemia have been linked to cognitive decline in elderly patients with OSA. Additionally, brain atrophy and reduction in gray matter volume have been attributed to OSA and are more pronounced with the severity of the disease. While some disruption of sleep is normal in healthy aging adults, the changes that Alzheimer’s patients experience tends to be more severe and disruptive. In healthy adults, aging is associated with a decline in overall sleep quality with less time spent in the restorative, deep stages of sleep. While sleep apnea is a risk factor for dementia more broadly, a staggering 40% of dementia patients have obstructive sleep apnea.
The bi-directional relationship between sleep apnea and neurodegenerative diseases has not been determined with Parkinson’s disease and will require further study. OSA can be seen in up to 66% of Parkinson’s patients, according to an NIH observational study. While OSA is associated with increased severity of Parkinson’s-related cognitive symptoms, further research is needed to determine if OSA actually accelerates the disease.
Treatment and Potential Reversal
There is encouraging news for neurologically healthy patients who suffer from obstructive sleep apnea as well as for Alzheimer’s and Parkinson’s patients who also suffer from OSA. Continuous Positive Airway Pressure (CPAP) treatment, the gold standard in sleep apnea treatment, has been shown to help stabilize blood oxygen levels, allowing healthy blood flow to the brain. CPAP delivers pressurized air through tubing and a mask worn while you sleep.
A series of studies at the University of Michigan’s Sleep Disorders Centers revealed that sleep apnea patients who consistently used CPAP were less likely to develop dementia or mild cognitive impairment over the next 3 years.
Research in conjunction with the American Academy of Sleep Medicine (AASM) was among the first studies to use neuroimaging to show brain damage reversal in patients with severe untreated sleep apnea who used CPAP. The reversal was minor at the 3 months mark, but after 12 months of CPAP use, the brain damage and abnormalities were almost completely reversed. These conclusions also revealed improvement in cognitive testing, better mood, less brain fog, and an overall improvement in quality of life.
Ongoing research continues to confirm sleep’s critical role in physical and mental health, including cognitive health. By proactively diagnosing and treating sleep apnea, further cognitive decline can be delayed and, in some cases, even reversed.