Sleep apnea and the risk of Alzheimer’s disease

Sleep apnea is a condition where normal breathing is interrupted throughout the night. There are three forms of sleep apnea: obstructive sleep apnea (OSA), central sleep apnea, and complex (or mixed) sleep apnea (a combination of the two). OSA is the most common of the three and occurs when the throat muscles relax causing a partial or complete obstruction of the airway for more than 10 seconds. This can reduce the level of oxygen that is in the blood and interrupt the normal sleep cycle. Estimates vary, but as many as 10% of adults in the United States may suffer from OSA and as many as 30-80% of elderly individuals may suffer from it [1]. However, up to 80-90% of cases may go undiagnosed [2].

OSA may increase the risk for several diseases including cardiovascular disease, hypertension, metabolic syndrome, cognitive dysfunction, and Alzheimer’s disease. It may also increase the risk for daytime sleepiness [3]. In individuals without Alzheimer’s disease, OSA was associated with deficits in attention and alertness, visual and verbal memory, and executive function. However, it did not affect language ability and motor function [4].

With regards to Alzheimer’s disease, a meta-analysis of nine observational studies suggested that OSA may increase the risk of cognitive decline or Alzheimer’s disease by more than two-fold, and another meta-analysis of five studies suggested the OSA is more prevalent in Alzheimer’s patients [5; 6; 7]. In addition, several studies suggest that cognitively healthy elderly individuals with OSA may have altered levels of Alzheimer’s disease biological markers (i.e., biomarkers) [1] and that a diagnosis of OSA may further impair Alzheimer’s biomarkers over time [8; 9].

Sleep apnea is usually diagnosed in a sleep clinic. Some of the signs/risk factors for OSA include snoring, daytime sleepiness, obesity, being male, and old age. When sleep apnea is diagnosed, the most common treatment is a continuous positive airway pressure (CPAP) device. A CPAP device includes a mask that continuously pushes air through the nose and mouth so that interruption of breathing does not occur throughout the night.

There is mixed data from randomized controlled trials on whether the use of CPAP improves cognition in adults with OSA. Several studies suggest that CPAP use improves some aspects of cognition such as attention and vigilance in healthy patients [10; 11]. Similarly, some studies suggest that initiation of CPAP treatment and better compliance of CPAP use in Alzheimer’s patients with OSA may improve some aspects of cognition, though the data is mixed [12; 13; 14; 15]. The difficulty in assessing these randomized controlled trials is that most of the studies are small and short in duration.

How might OSA increase the risk of Alzheimer’s disease? Interruptions in breathing can reduce the levels of oxygen in the blood which could damage brain cells. In addition, OSA is associated with several other diseases, such as hypertension, cardiovascular disease, and depression, that can increase your risk for Alzheimer’s disease. Finally, a good night of sleep is important for several brain processes, such as the consolidation of memories. Interruption of sleep due to OSA may impair these processes [9].

If you snore, are tired throughout the day, or have other sleep issues, consider going to a specialist in sleep disorders usually at specialized sleep centers. They may suggest that you undergo a sleep study to diagnose whether you have OSA and can provide potential treatment options. According to the National Heart, Lung, and Blood Institute, some cases may be treated with lifestyle changes such as weight loss, regular physical activity, less alcohol consumption, quitting smoking, and better sleep habits. More serious cases may need to be treated with the use of a CPAP device, a mouthpiece to prevent the tongue from blocking the upper airway, or with surgery. A healthy night of sleep is important for brain health, and undiagnosed sleep apnea may be one way sleep problems could be affecting the brain.

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