Lack of sleep causes inflammation
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Q: Is the association of poor sleep and a higher risk of cognitive decline related to chronic inflammation?
A: 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. That leads 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.
Q: In the past, I have sometimes seen streaks in my vision. They go away so quickly I don’t know if it is in one or both eyes. But now I have a lacy black spot in my right eye that I only see sometimes. Are they related?
A: What you describe sounds like flashes and floaters. Both commonly happen as we get older.
The eye consists of two major compartments — the front (including the cornea, iris and lens) and the back (the rear two-thirds of the eyeball, including the retina and a large cavity filled with vitreous gel that attaches to the retina).
Flashes, the quick streaks of light you describe, tend to be most noticeable in the dark. They occur when the vitreous gel bumps, rubs, or tugs against the retina. This action can lead to small areas of vitreous detachment, a sudden separation between the vitreous gel and the retina.
The small black spot you see in one eye sounds like a typical floater. People often notice occasional floaters — spots, squiggly lines, rings or opaque flecks — drifting across their line of vision.
Floaters are tiny clusters of cells or clumps of gel that have formed in the vitreous cavity. What the person sees is the shadow that these little clumps cast on the retina.
People often become more aware of floaters when they look at a book page, a computer screen, or a solid, light-colored background. Floaters can also be more noticeable when you’re tired.
Unlike flashes, floaters don’t disappear. However, over time, they become much less noticeable for several reasons. The brain eventually filters out unimportant or repetitive information, including floaters. The clumps of gel can also shift position and move away from your central vision.
Occasional flashes and one or two small floaters are generally harmless.
However, certain features may signal a retinal detachment, a potentially serious problem where the retina tears away from the back of the eye. Immediately call for medical advice if you experience any of the following:
- Many flashes occur at once or in rapid sequence
- Two or more floaters suddenly appear in the same eye
- A shadow develops in your peripheral vision
- A dark “curtain” covers some of the vision in one eye
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, see health.harvard.edu.
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