Sleep problems, Alzheimer's disease are related, but which one comes first?

A new article explores the pathophysiological factors that link sleep disorders and Alzheimer's disease. A better understanding of this link could lead to diagnoses and potential treatments for Alzheimer's disease and other neurodegenerative diseases and dementia. The article is published before printing in the Journal of Neurophysiology.

Alzheimer's research is largely focused on the presence of two proteins – the beta-amyloid protein and the tau protein – in the brain. Amyloid beta appears to be involved in learning and the brain's ability to change and adapt, and tau helps regulate normal signaling between neuronal cells. People with Alzheimer's disease have been found to have two features: an accumulation of beta-amyloid and tau tangles in the brain.

Previous studies on animals and healthy humans have reported higher levels of beta-amyloid after a single night of sleep deprivation. This is consistent with patterns of normal protein fluctuation that occur before sleep and waking. These findings suggest that sleep helps the body eliminate excess beta from amyloid before it accumulates too much in the brain. Research has also shown that disruption of slow-wave sleep – a phase of deep sleep – results in an increase in amyloid beta levels of up to 30%. "This evidence demonstrates the importance of sleep in the elimination of metabolic waste and sleep disturbances as an important mediator in the development of [Alzheimer’s disease], "Wrote Shen Ning and Mehdi Jorfi, Ph.D., the authors of the article.

The presence of tau – the tangled protein in the brains of people with Alzheimer's disease – in the fluid that surrounds the brain and spinal cord (cerebrospinal fluid) is a marker of nerve cell injury, explained the authors. Sleep deprivation for one night only resulted in increased tau levels of up to 50% in cerebrospinal fluid.

Research suggests that an increase in beta-amyloid and tau production and reduced elimination of these proteins are the major contributing factors to Alzheimer's disease. If quality sleep seems to help the body eliminate excess protein, it remains to be determined whether sleep disturbances worsen [Alzheimer’s disease] symptoms and increases the progression of the disease, or if the sleep disturbance actually triggers the cascade of [Alzheimer’s disease] development, "the researchers wrote.

The continuing study of the relationship between sleep and Alzheimer's disease "holds great promise for bridging the gap between molecular and cellular sleep biology in the context of the development of [Alzheimer’s disease]. It can even offer therapeutic benefits useful for preventing not only [Alzheimer’s disease]but also to improve the diagnosis and treatment of psychiatric and metabolic diseases, "the researchers wrote.

Provided by
American Physiological Society