Skip to main content

Verified by Psychology Today


Out-of-Sync Circadian Rhythms Link With Weight Gain in Mice

Is a correlation between sleep patterns and building of fat cells surprising?

Key points

  • Recent studies on mice suggest that a disruption of circadian rhythms correlates with formations and growth of fat cells. 
  • Current research examines correlations between circadian rhythms and many other health-related body functions.
  • Correlations give links that conjecture a cause. Causes are far harder to know.
 NIGMS, Public Domain
master clock coordinating biological clocks from daylight
Source: Source: NIGMS, Public Domain

Do this: Stand outside in daylight, close your eyes, and wave your hands in front of your eyes to cover and uncover your eyelids. You will experience a difference in the amount of light coming through your eyelids. That’s because your eyelids are 20 percent transparent, so morning light hits the ocular nerves to signal to the body that it’s time to wake and get things moving. It is a mechanism of natural selection survival, a convenient hang-on from primitive times that relied on sunlight sensitivity to separate a sleeping body’s distinction of nighttime from daytime. One might think that those human survival features are no longer necessary since we no longer sleep in caves near saber-toothed tigers.

Evolution of sleep functions

Why are regular sleep cycles that are in sync with night and day rhythms so beneficial when we have artificial light whenever we need it? The answer is that, through millions of years of evolution, our cells have developed to function according to circadian rhythms, building, using, and flushing out proteins to keep our bodies fit.

When ganglion cells in the retinas containing light-sensitive pigments are exposed to daylight, they signal the pineal gland to suppress the secretion of melatonin. In the darkness, that secretion is activated. It is a circadian clock that is reset each morning, ready to go through its daily cycle: In summer months, melatonin production begins around 8:00 p.m., peaks at about 3:00 a.m. to give the deepest sleep, and ceases at about 8:00 a.m. But it’s not just about the secretion of melatonin; heartbeat rates and body temperatures also are regulated by clock cells in the body, all tuned by the master clock in the brain, the suprachiasmatic nucleus that sits in the hippocampus, quite close to the pineal gland.

So it is no surprise to find that circadian rhythms are critical to body health.

After some thoughts and investigations on the connections between circadian rhythms and Alzheimer's disease, I looked elsewhere for whatever I could find in the current scientific research connecting circadian rhythms to health. I went to my most trusted sources, which included the Proceedings of the National Academies of Science and Cell Reports. As the author of a book involving circadian rhythms, I knew that whenever our master body clocks are out of sync with circadian rhythms, the cells of our bodies struggle to maintain their health-maintaining functions. It’s general knowledge that when a scientific experiment finds a correlation between X and Y, one should look for correlations between X and anything one can think of that might have a possible connection to X.

What is known

We learned that there are correlations between circadian rhythms and Alzheimer’s disease but whenever we look for a correlation between circadian rhythm body synchronization and other conditions, we find them. Now we are finding relations with stress, excess blood sugar, metabolic changes and disruptions, glucose production in the liver, cell growth, metabolism disorders, and tumor progression. Some recent studies on mice suggest that a disruption of circadian rhythms correlates with formations and growth of fat cells.

We know that the purpose of the body clock is to maintain physiological stability. And we also know that when that clock gets offset, it loses its ability to maintain synchrony with cells whose functions are critical to life.

So this post takes off from previous ones—“Why Are We So Worried About Dementia Correlations?” and “Is Alzheimer’s Related to Disruptions of Circadian Rhythms?—giving us some thoughts about how circadian rhythms connect to Alzheimer’s disease.

Organisms perform best at certain hours of the day

Almost all animals have internal daily rhythms. The human mind and body have a built-in circadian system, a coordinated assembly motivated to perform certain tasks, what might be called the macrobiological clock. At the molecular level, there is a circadian oscillator, specific cell groups that work together, like the mechanism of a clock, to cause a larger system of mind and body to function in a daily rhythm.

Joseph Mazur
Internal daily rhythms
Source: Joseph Mazur

Say you wake at 6:00 a.m. By 7 or 9 a.m., your blood pressure will increase as your melatonin secretion decreases. Your alertness is at its maximum after 10 a.m., and coordination is best after 2 p.m. By around 3 p.m., your reaction time and cardiovascular efficiency are at their height, and by 6 p.m., blood pressure and body temperature are at their highest. Then, by around 9 p.m., melatonin secretion begins to start the cycle over again.

So it’s not surprising to find correlations between circadian rhythms, body functions, and physical behavior trends. The latest research list includes correlations with erratic sleep schedules, fat cell production, stress, brain plaque, and tumors in cancer patients. When clock genes are unsynchronized, immune systems and muscle and skin health processes suffer.

Take it from me: “We might think that we have control over time’s grip on our will and behavior, that time has some feeble influence over body functions vulnerable to willful suppression, and that biological links from the mind and body to the external circadian cycle are too delicate to be taken seriously. Not true. The biochemical and genetic structure seems to be stronger than we suppose.”

Research suggests connections that hint at causes. There is no direct evidence that irregular sleep cycles cause Alzheimer’s disease, nor is there any direct evidence that body cells unsynchronized to circadian rhythms effectively build fat cells. We have a long way to go before having any direct implications. 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. So we can and should learn more, as we always do with the tools and methods of good science.


Joseph Mazur, The Clock Mirage (New Haven: Yale, 2020) 108.…

More from Joseph Mazur
More from Psychology Today