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Why Are We So Worried About Dementia Correlations?

Is a correlation between irregular sleep and Alzheimer’s dementia surprising?

Key points

  • There is no direct evidence that irregular sleep cycles cause Alzheimer’s disease, but there are correlations.
  • Sleep irregularities can increase plaque deposits, which does hinder cerebral functioning.
  • Recent research found a 40 percent higher risk of developing Alzheimer’s disease for older people napping more than an hour each day.
 Unknown source/Wikimedia Commons, public domain
Auguste Deter. First Alzheimer’s Patient (1901)
Source: Unknown source/Wikimedia Commons, public domain

I am at the age when my friends get concerned about dementia. They forget the name of a familiar place or of a recently introduced acquaintance. Filler words become more frequent. Correct words take more time to be retrieved. That is not so for my grandchildren, who go on with their rapid raps without hesitation, relying on the term "basically," a word that has lost much of its meaning as it spread in overuse across a few of the younger generations.

This post takes off from two previous ones—“Circadian Rhythm Connection to Alzheimer’s” and “Is Alzheimer’s Related to Disruptions of Circadian Rhythms?"—giving us some thoughts about how circadian rhythms connect to Alzheimer’s disease. Those posts suggest connections that hint at causes. There is no direct evidence that irregular sleep cycles cause Alzheimer’s disease. We know that sleep is a critical element in sustaining brain health. We also know that sleep irregularities can increase plaque deposits, which does hinder cerebral functioning.

Whenever I hint to old friends that irregular sleep patterns correlate with Alzheimer’s dementia, I see squinting eyes and a worried look from those who have trouble sleeping. A half-century ago, correlations with Alzheimer’s dementia was the aluminum in pots and soda cans. After that, the next guilty substances became antacids and antiperspirants. Next came dental fillings and flu shots, all discredited. In fact, for vaccines, the opposite is true. Older adults vaccinated against polio and influenza seem to have a reduced risk of developing Alzheimer’s dementia compared to those not vaccinated.

Risks of Daily Naps?

And now, we are seeing studies pointing to the hazards of taking regular naps. What?! Yes. A recent article in The Journal of the Alzheimer’s Association suggestively reports a 40 percent higher risk of developing Alzheimer’s disease for older people napping more than an hour each day. Peng Li, assistant professor of medicine at the Harvard Medical School, and his research team correlated daytime napping and Alzheimer’s dementia. His 14-year study of 1,401 participants found a “correlation with worse cognition a year later, and conversely, worse cognition was correlated with more excessive naps a year later.”

No Claim of Cause

Clearly, Peng Li’s experienced research team considered that participants of the study tended to have minor cognitive impairments and might also have one of the typical symptoms of Alzheimer’s dementia, namely fatigue. The newsflashes, however, tend to punch a bit more fright to the readership.

But another team of researchers led by Christine Walsh, an associate professor of neuroscience at the University of California, San Francisco, claims that for Alzheimer’s patients who need to nap for long periods, the disease has damaged neurons that keep them awake. “You can think of this system as a switch with wake-promoting neurons and sleep-promoting neurons, each tied to neurons controlling circadian rhythms,” said Joseph Oh, one of the lead authors on Walsh’s team.

Role of Irregular Sleep Cycles

As I mentioned in my previous post—“Is Alzheimer’s Related to Disruptions of Circadian Rhythms?”—the more likely culprit is the rogue protein beta-amyloid, which is associated with neurodegeneration. In the daytime, beta-amyloid accumulates in the brain. At night, the healthy brain clears it out. Some researchers claim that sleep disruption occurs from a beta-amyloid plaque buildup that causes subcortical neurons to degenerate. Ah, so with irregular sleep, that plaque is not cleared out.

Alongside the beta-amyloid is the tau protein, “a critical driver of sleep disturbances.” A curious picture comes from patients with serious difficulties sleeping, some of whom hardly ever sleep. Walsh’s study measured the amounts of beta-amyloid and tau proteins. The expectation was that, for sleep-deprived patients, there should be plenty of beta-amyloid, and, yet, it turns out that there was none.

Sleep or No Sleep

So it does seem, as the Peng Li article title tells us, that daytime napping and Alzheimer’s dementia are potentially bidirectional.

I’m always skeptical of how correlations tend to be biased toward connecting causes. Correlations can be coincidental data matches. They happen far more frequently than we believe. Surely, irregular sleep cycles do not cause Alzheimer’s disease, though tampering with circadian rhythms meddles with health well-being, specifically with cognitive-function health.

The correlation between irregular sleep patterns and Alzheimer’s dementia is not surprising. But whenever one correlation is found, others are being uncovered and investigated. We now have more than 16 peer-reviewed studies associating vision impairment with a significantly increased risk of dementia. Next up are wine and Alzheimer’s. Wine?! Recent studies connect a glass of wine a day to Alzheimer’s dementia. Science is complicated. There are correlations between wine and sleep, so why not wine and Alzheimer’s? Is the culprit wine, sleep, or something else?

So if you are worried about the future of your mental acuity, you might want to get your sleep cycle into synch with your body's needs.

Be reassured, though, that a few blips in word retrieval do not score a hint of mental troubles ahead. Those hiccups are—basically—signals of age advancement.


Joseph Mazur, Fluke: The Math and Myth of Coincidence (New York: Basic Books, 2016).

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