The connections between poor sleep and cognitive decline and inflammation are profound. Dr. Howard LeWine of Harvard Health explains.
Question: Is the association of poor sleep and a higher risk of cognitive decline related to chronic inflammation?
Answer: Sleep deprivation is a condition that occurs when you don’t get enough sleep, or enough good quality sleep. Research has found that sleep deprivation is associated with markers of inflammation, such as increases in inflammatory molecules — including cytokines, interleukin-6, and C-reactive protein.
While these signs of inflammation could be attributed to other factors — stress, smoking, or obesity, for example — they do suggest that sleep deprivation plays a role in the inflammatory process. Inflammation is the body’s natural response to disease and injury; it is usually a temporary response and serves as an effective defense mechanism. But when inflammation doesn’t let up, it contributes to the development of heart disease, diabetes, stroke, cancer, and Alzheimer’s disease.
How does a lack of sleep contribute to inflammation? One theory focuses on blood vessels. During sleep, blood pressure drops and blood vessels relax. When sleep is restricted, blood pressure doesn’t decline as it should, which could trigger cells in blood vessel walls that activate inflammation. A lack of sleep might also alter the body’s stress response system.
In addition, a sleep shortfall interferes with the normal function of the brain’s housecleaning system, termed the glymphatic system (not to be confused with the lymphatic system in the rest of the body). In the deepest sleep phases, cerebrospinal fluid rushes through the brain, sweeping away beta-amyloid protein linked to brain cell damage.
Without a good night’s sleep, this housecleaning process is less thorough, allowing the protein to accumulate — and inflammation to develop. Then, a vicious cycle sets in. Beta-amyloid buildup in the brain’s frontal lobe starts to impair deeper, non-REM slow-wave sleep. This damage makes it harder both to sleep and to retain and consolidate memories.
Just one night of lost sleep can keep beta-amyloid levels higher than usual. The problem is not so much a single night’s poor sleep, which you can compensate for, but a cumulative pattern of sleep loss, leading to decreases in the structural integrity, size, and function of brain regions like the thalamus and hippocampus, which are especially vulnerable to damage during the early stages of Alzheimer’s disease.
Related: 10 Habits for a Healthy Brain
Howard LeWine, M.D., is an internist at Brigham and Women’s Hospital in Boston and assistant professor at Harvard Medical School. For additional consumer health information, please visit www.health.harvard.edu.
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