How Circadian Rhythms Affect Your Body Weight

How Circadian Rhythms Affect Your Body WeightYou may not be aware of it but your body has an internal clock that regulates its activities. This clock adjusts itself based on cues from the environment, particularly exposure to light and dark. It’s this clock that sets your circadian rhythms, 24-hour rhythms that affect your emotional and physical health. For example, circadian rhythms regulate the release of hormones and impact fertility, immunity, digestive function, body temperature, the sleep-wake cycle, and your mood. What’s not so good is when circadian rhythms get “out of whack.” Abnormal circadian rhythms are linked with problems like insomnia, fatigue, depression and type 2-diabetes. Now, a new study shows that disruption in circadian rhythms also leads to weight gain.

Where is Your Internal Clock Located?

Your internal clock is a group of nerve cells located in a portion of your brain called the suprachiasmatic nucleus. This tiny cluster of nerve cells, no larger than a grain of rice, has a lot of influence since it regulates a variety of hormones and brain chemicals. For example, it indirectly controls the release of the stress hormone cortisol. Knowing that it’s easy to see how disrupting this clock could lead to problems.

One way this can happen is when you expose your eyes to light when you would normally be sleeping. Working night shifts, staying up late at night and crossing time zones during travel all disrupt normal circadian rhythms. How can this impact your health and lead to weight gain?

Circadian Rhythms, Weight Gain and Obesity

Researchers at Leiden University Medical Center in the Netherlands exposed mice to constant light, 24 hours a day. This change had major consequences for their metabolic health. The mice exposed to constant light became less sensitive to insulin and began eating more. Plus, their resting metabolism dropped by 13% and they gained weight almost immediately. The mice had lost the normal variation in insulin sensitivity that occurs over a 24-hour period and they became more efficient at storing fat.

Mice aren’t the only species that are affected by changes in circadian rhythms. Researchers at the Brigham and Women’s University Medical Center in Boston looked at the effects of circadian rhythm changes on a group of women participants by altering their sleep patterns. The women slept at intervals typical of rotating shift workers and people crossing time zones when traveling. During these periods of irregular sleep, the volunteers showed a rise in blood glucose and a drop in their metabolic rate. As the researchers pointed out, the change in metabolic rate would be enough to cause a weight gain of 12 pounds per year. Pretty scary, huh? Fortunately, this was reversed after they began sleeping normally again.

 What Does This Mean?

Keeping your internal clock “properly set” is vital for your metabolic health and for controlling your weight. This means getting enough sleep and not “burning the midnight oil.” When you go to sleep matters too. A hormone called melatonin is linked with your internal clock. Melatonin is released when your eyes aren’t exposed to light, at night when you’re sleeping, but it’s turned off by exposure to light. Melatonin release peaks between the hours of 12:00 A.M. and 2:00 A.M. If you’re awake during those hours, your melatonin level will be lower. Why is this bad? Melatonin is a strong antioxidant and low levels have been linked with type 2-diabetes and breast cancer in women.

Going to bed early, sleeping in a dark room to maximize melatonin production and getting enough sleep are all important for preventing insulin resistance and controlling your weight. Not sleeping enough has already been linked with weight gain and type 2-diabetes. When you go to sleep matters when it comes to your metabolic health. Staying up at night and working late shifts disrupts your natural biological clock and reduces the amount of melatonin your brain releases. It’s even more critical to turn in early as you get older since you produce less melatonin with age.

The Take-Home Message?

Make sure you’re turning in early, sleeping in complete darkness, going to bed as early as possible and getting at least 7 hours of sleep a night. Do it to control your weight – and for your health.



The FASEB Journal vol. 27 no. 4 1721-1732. (2013)

Journal of the American Medical Association News. “Disrupting Body’s Biological Clock May Increase Risk of Weight Gain, Diabetes”

WebMD. “Hormone Melatonin & Type 2 Diabetes May Be Linked”


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Light Exposure and Body Weight: Is There a Link?

Does When You Eat Your Meals Impact How Much Weight You Lose?

How Desk Jobs Make It Harder to Lose Weight and How to Avoid the Pitfalls

How Does Lack of Sleep Affect Your Metabolism?

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