Sleep apnea is a serious sleep disorder affecting over 30 million people in the US and over 1 billion globally. Obstructive Sleep Apnea (OSA), the most prevalent type of sleep apnea, is characterized by frequent, repeated interruptions in breathing during sleep. While it is commonly associated with nighttime snoring and daytime sleepiness, new research shows that sleep apnea’s effect on cognitive function may actually lead to Alzheimer’s, the most common form of dementia.

Understanding Alzheimer's and Dementia

According to the Alzheimer’s Association, over 6 million Americans aged 65 and over suffer from Alzheimer’s disease. It is estimated that by the year 2050, the number of Americans with this disease could reach over 14 million. Alzheimer’s is a degenerative brain disease caused by cell damage and the resulting changes in the brain. Often used interchangeably with Alzheimer’s disease, dementia is a broader term used to describe the symptoms of cognitive decline, such as loss of memory, as well as compromised reasoning and learning skills.

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. A study done at the Turner Institute for Brain and Mental Health found that severe obstructive sleep apnea is linked to an increase in this protein. 

Sleep Apnea and Cognitive Decline

New research is finding strong connections between sleep disorders and neurodegeneration. The location in the brain that reflects cognitive decline and the manner in which the damage spreads is 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. 

The relationship between sleep apnea and dementia is also bidirectional due to the changes in circadian rhythm and actual sleep structure that occur in dementia patients. Circadian rhythm is a series of physical and psychological processes that guide our sleep-wake cycle. Research has uncovered damage in the area of the brain that responds to environmental cues such as light, which are critical in facilitating our sleep-wake cycle. Because of this damage, dementia patients often don’t have a typical 24-hour sleep-wake cycle and spend much more time sleeping during the day than at night. The actual sleep structure in dementia patients is also different, resulting in lighter, less restorative sleep.

The Impact of Sleep Apnea on Dementia Patients

We usually experience four cycles of sleep throughout the night, ranging from the initial lighter phases of sleep to the deeper, dream-enhanced phases. Because dementia patients spend more time in the lighter phases of sleep, they do not benefit from the restorative deep sleep phases, which are linked to the cleansing of toxins and cell regeneration. While some sleep disruption is normal in healthy aging adults, the changes that dementia patients experience tend to be more severe and disruptive. While sleep apnea is a risk factor for dementia, a staggering 40% of dementia patients have obstructive sleep apnea.

CPAP Use and its Effect on Cognitive Impairment

There is encouraging news for neurologically healthy patients who suffer from obstructive sleep apnea as well as for dementia patients also suffering from OSA. Continuous positive airway pressure (CPAP) treatment has been the gold standard in sleep apnea treatment. CPAP works by pressurizing and filtering the air and delivering it through a hose and mask that you wear on your face while sleeping. CPAP keeps airways open and improves breathing quality, which leads to improved sleep. When breathing is disrupted repeatedly throughout the night, blood oxygen levels drop, and blood flow to the brain is reduced. CPAP helps bring blood oxygen levels back, allowing healthy blood flow to the brain.

Results from a study done at the University of Michigan’s Sleep Disorders Centers found that people who consistently used CPAP were less likely to develop dementia or mild cognitive impairment over the next three years. Results from a study by the American Academy of Sleep Medicine (AASM) were the first to use neuroimaging to show brain damage reversal in patients with severe untreated sleep apnea who used CPAP. At the three-month mark, the reversal was minor, 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.

Because sleep apnea and dementia are often concurrent, CPAP treatment can help not only with sleep apnea symptoms but can help to reduce the risk of dementia or the progression of the disease. The current research confirms the importance of sleep and its connection to overall good health.