A strong, consistent sleep cycle has been linked to improved mood, lower stress levels, a healthier heart and stronger immunity.
Now, researchers are beginning to understand more clearly how the body’s circadian rhythm — which controls our sleep-and-wake cycle via a kind of 24-hour internal clock — impacts brain health in a disease like Alzheimer’s.
According to a study published in PLOS Genetics, based on research conducted at the Rensselaer Center for Biotechnology and Interdisciplinary Studies, the cells that clean up beta-amyloid plaques in the brain — the accumulation of which is commonly found in people with Alzheimer’s disease — follow a 24-hour circadian rhythm. This could mean that disruption in that circadian rhythm could also disrupt those cells’ ability to remove the plaques, theoretically leading to cognitive issues such as memory loss.
To conduct their study, researchers looked at macrophages in mice. Macrophages are a kind of immune cell that removes other dead or unwanted cells, such as beta-amyloid plaques, by “ingesting (them) in a process called phagocytosis,” according to the Rensselaer Center.
Observing these macrophages, researchers found that their ability to clear beta-amyloid changed over the course of a 24-hour period. Proteins on the surface of the macrophages also followed a kind of 24-hour cycle. The study found that within that 24 hours of those proteins being at their lowest levels, the ability to clear the damaging beta amyloids was at its highest, and vice versa. They also noted that when that circadian rhythm was disrupted, the clearance of the damaging beta-amyloid didn’t work as normal.
These findings are in line with other studies that found that brain macrophages called microglia also follow a circadian rhythm that regulates their immune response and function, as reported by The Conversation.
“It’s possible that microglial circadian rhythm may also even be involved in the control of neuronal connectivity — which might contribute to the worsening of Alzheimer’s-related symptoms, or even sleep issues that older people might exhibit,” the article said.
This study was limited in that it only looked at single cells, rather than full systems, and the mice macrophages used in observation weren’t brain-specific.
But even in studies that do look at full organisms, “the results about the relationship between Alzheimer’s and circadian rhythm are more conflicting — they often fail to portray all the issues found in humans with Alzheimer’s disease, as they only study specific systems or proteins that might be affected by Alzheimer’s disease. This means they aren’t a fully accurate representation of how Alzheimer’s occurs in humans.”
Scientists are still working out what role exactly the circadian rhythm plays in the development or worsening of Alzheimer’s disease. What they do know, however, is that quality, consistent sleep is good for overall health, and that our brains are healthier when we rest well.
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