In Beating the Dementia Monster, we discussed very recent findings on the role that sleep, especially deep sleep, plays in Alzheimer's disease. It's in deep sleep that the shrinkage of neurons and the slowed rhythm of brain waves promotes the clearing of trash from the brain. That trash includes both the beta amyloid peptides and tau protein tangles that are part of the progress of the disease. We said that good sleep is really important to resisting both the initiation and progress of Alzheimer's disease.
But who gets a good night's sleep any more? As Dr. Matthew Walker wrote in his best-selling book Why We Sleep, as we get older, our brains atrophy, and the part of the brain that controls sleep becomes less effective. In Alzheimer's disease, the atrophy accelerates, and our ability to sleep well is increasingly impaired.
Another factor in sleep is our circadian rhythm that governs many functions of our bodies throughout the 24-hour day. This includes when our bodies are interested in sleep and when they will insist on waking up. Walker cites the "Early Bird Specials" at restaurants that appeal to older people. He says that, as we age, our circadian rhythms advance, so that we want to go to bed earlier -- and get up earlier. (And so older restaurant customers want to eat earlier.) If we don't go to bed earlier, we'll still awaken earlier and get less sleep. I used to go to bed at 11, but I deliberately changed my bed time to 9:15, although I have a hard time getting my head on the pillow before 9:30. To fight insomnia, I try to stay as consistent with my bed time as I possibly can.
But is there one circadian rhythm for the whole body, or do many parts have their own control systems?
My friend Teale recently sent me an article from The Conversation about research on rhythms that can be traced to the cells, especially certain white blood cells called macrophages. As we learned in high school biology, white blood cells play a role in the immune system. Like amoebas (and The Blob), they engulf and absorb their prey. Back in July 2020 we wrote about "cytokine storms" and their complex relationship to both the beneficial and destructive roles of inflammation in the brain. The cytokines arise from the macrophages.
The article was based on this research which you may -- or may not -- want to read. I leave it to you to decide. It's called "Circadian control of heparan sulfate levels times phagocytosis of amyloid beta aggregates."
The researchers gave macrophages from mouse brains the opportunity to eat up amyloid beta molecules. They found that they devoured the molecules differently at different times of the day, and the timing was controlled by molecules in the cells that apparently respond to the body's circadian rhythm. This seems to be synchronized with the periods of sleep most noted for controlling Alzheimer's disease.
We have, of course, our standard disclaimer on mice: Mice are not people. Many discoveries made with mice turn out later to be unrelated to how the human brain behaves.
Nevertheless, we know for sure that getting good sleep fights Alzheimer's disease.
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