How does melatonin affect metabolic health?

The hormone most closely associated with sleep also seems to impact glucose and insulin. Here’s what we know.


Article highlights

  • Melatonin, a hormone naturally produced in the brain, signals your body that it’s time to sleep. Levels of melatonin in the blood are highest when it is dark and low throughout the daytime.
  • Various factors can affect our melatonin levels and throw off our circadian rhythm, or internal 24-hour clock. These include daily activity levels, sleep patterns, body temperature, and light patterns.
  • There is no consensus in the research on the relationship between melatonin levels and glucose. Some studies suggest higher melatonin levels benefit metabolic health, while others show it is harmful.
  • Some researchers hypothesize that food intake may play a role. Specifically, elevated melatonin levels around the time of eating, such as if you have a late dinner, may impair glucose tolerance.
  • Learning more about your melatonin levels may help you time meals. You can either ask your doctor or use an at-home blood testing service. A continuous glucose monitor will also allow you to see patterns in your glucose levels.
  • TAKEAWAY: Melatonin plays a crucial role in your circadian rhythm and may also impact blood sugar levels.

Melatonin plays a vital role in the sleep-wake cycle. The hormone occurs naturally in the body and can also be taken in supplement form to address jet lag, sleep disorders, and other sleep issues.

Research suggests melatonin may also affect glucose levels in the body, but studies have yielded contradictory findings as to whether the impacts are beneficial or harmful to metabolic health.

This article will walk through what the scientific literature says thus far on the relationship between melatonin and glucose and how we may be able to utilize that information to get a better night’s sleep and work towards optimizing metabolic health.

What is Melatonin?

Melatonin is a hormone that the brain naturally produces. It signals to your body that it’s time to sleep by acting on the melatonin receptors, known as MT1 and MT2, in the brain. Levels of melatonin in the blood are highest when it is dark and help regulate the circadian rhythm by making you feel sleepy at night. Throughout the day when it is light outside, melatonin levels are naturally low.

Various factors can affect the amount of melatonin our brains produce and potentially throw off our circadian rhythm. These include activity levels throughout the day, sleep patterns, body temperature, and light patterns. For example, darkness at night triggers melatonin production in the brain, while light during the day activates a signal to stop releasing melatonin. If this pattern is disrupted, the brain may produce melatonin at the wrong times. Major disruptions, like jet lag, can also throw melatonin levels out of whack.

In recent years, taking melatonin as an over-the-counter supplement has become increasingly popular in an attempt to recalibrate melatonin levels in the body and address issues like restlessness and insomnia. While short-term use of supplemental melatonin at optimal dosages is generally considered safe, there is not enough research to determine its true health effects when used long-term.

One area of research looking at the health impacts of melatonin levels focuses on metabolic health.

How Melatonin Affects Blood Sugar: What the Research Shows

Numerous studies have been conducted looking at how melatonin levels affect glucose. To date, no consensus has been reached. Some studies have yielded findings that higher melatonin levels are beneficial to metabolic health while others show it has a harmful effect.

For example, some research suggests that at a cellular level, melatonin is important for the survival and function of beta cells, which are responsible for producing insulin, the hormone that controls the level of glucose in the blood.

Additionally, a study published in JAMA found that low levels of melatonin in the blood were independently associated with an increased risk of insulin resistance (meaning that insulin is not as effective at shuttling glucose into cells so the body has to produce more insulin to manage blood sugar levels) and Type 2 diabetes. Another study published in the American Journal of Epidemiology looked at 1,075 generally healthy, non-obese women. The researchers found that higher nighttime melatonin levels were linked to greater insulin sensitivity and a lower prevalence of insulin resistance.

“You’ll want to avoid eating when melatonin levels are naturally high, like at nighttime. This would mean eating an earlier dinner and avoiding late-night snacking.”

Other research suggests melatonin can have a negative impact on metabolic health. For example, one study published in Cell Metabolism that used both mouse and human models found that increasing levels of melatonin negatively impact the ability of beta cells to produce insulin. The researchers determined that the effect is stronger in people with a variant in the melatonin receptor gene MTNR1B, which is linked to a higher risk of Type 2 diabetes. But the study also found that insulin inhibition may also have a positive effect in some cases. The authors concluded that reduced insulin release at night when melatonin levels are high but metabolic demand is low (because food hasn’t been consumed recently) may be a protective mechanism against nocturnal hypoglycemia, or low blood sugar levels at night.

In a study published in the journal, Clinical Endocrinology researchers administered either 1 mg of melatonin or a placebo to 22 postmenopausal women first thing in the morning. The participants then underwent glucose tolerance testing 45 minutes later. The researchers found that those who received the melatonin had reduced glucose tolerance and insulin sensitivity.

Another study of 21 healthy women published in the journal Sleep concluded that supplemental melatonin impairs glucose tolerance in both the evening and the morning. Researchers primarily focused on two important measures: the incremental area under the curve (AUC), which is an index that describes the total rise in glucose over time and is widely used to diagnose impaired glucose tolerance, and maximum concentration (Cmax) of plasma glucose.  In the evening, melatonin decreased insulin sensitivity, so insulin was less efficient at moving glucose out of the bloodstream, leading to increased glucose AUC by 54% and Cmax by 27%. In the morning, melatonin decreased glucose tolerance by decreasing insulin release, with an impressive effect: increased glucose AUC by 186% and Cmax by 21%.

How Timing May Play a Role

A number of factors are likely at play that may explain the conflicting research results described above. These include differences in study design, characteristics of the study population, such as sex, age, and underlying health conditions, and whether the study looks at naturally occurring melatonin or supplemental melatonin (as well as differences in doses and formulation when looking at the latter).

However, in a 2020 research paper published in the journal Trends in Endocrinology & Metabolism, the authors propose another theory: the Timing Model. The researchers hypothesize that food intake plays an important role in the impact of melatonin on metabolic health. Specifically, the theory states that elevated melatonin levels around the time of eating impair glucose tolerance. This could be the result of eating a late dinner or having higher levels of melatonin during the day (if the circadian rhythm is thrown off and the brain starts producing melatonin during daylight hours or if melatonin supplements were administered during the day, for example.) “Under both circumstances, the high melatonin levels may suppress insulin release and/or insulin sensitivity, resulting in impaired glucose tolerance,” the researchers write.

The authors are careful to acknowledge that other factors are at play and more research is needed to prove their hypothesis. However, they back up their theory with examples of previous studies. The American Journal of Epidemiology study, which concluded that higher melatonin levels are linked to greater insulin sensitivity and a lower risk of insulin resistance, for instance, measured nocturnal melatonin levels. Similarly, the JAMA study that found lower melatonin secretion to be associated with an increased risk of Type 2 diabetes, also relied on first-morning urine samples, a well-studied marker used to estimate overnight melatonin levels.

Another study published in the journal Clinical Nutrition supports the Timing Model theory. The researchers concluded that eating a late dinner—when melatonin levels in the body are naturally higher—resulted in impaired glucose tolerance.

How Can I Use This Information to Optimize My Melatonin Levels for Metabolic Health?

Learning your melatonin levels requires a blood test. If you’re curious about yours, you can either ask your doctor or use an at-home blood testing service. A continuous glucose monitor or glucometer will also allow you to see patterns in your glucose levels.

There is no universally accepted “optimal” level of melatonin. In fact, melatonin levels change on a daily basis and are highly individual to each person. The best way to test your melatonin levels is to take multiple readings at different times to see what your body would normally produce throughout the day and night.

If the Time Model hypothesis is correct (though again this still needs to be proven with large studies), there may be steps you can take to keep melatonin at your optimal levels and subsequently have a better effect on your body’s blood sugar levels.

The first is to pay close attention to meal times. You’ll want to avoid eating when melatonin levels are naturally high, like at nighttime. This would mean eating an earlier dinner and avoiding late-night snacking, which may result in better glucose tolerance. Doing this may also have additional health benefits, as studies show late dinners may impair glucose tolerance and promote obesity. Melatonin levels are typically still elevated early in the mornings so moving breakfast slightly later (rather than immediately after waking up) may also improve glycemic control.

When it comes to melatonin supplementation, timing should also be considered. According to the Timing Model hypothesis, you’ll want to space out the time between taking melatonin and when you eat. Ideally, melatonin administration would be separated by at least two hours from food intake, the researchers say.

If eating late, it may also be possible to manipulate melatonin levels through bright light exposure. However, this isn’t advisable, as suppressing melatonin levels at night can disrupt sleep, which may be associated with negative health consequences.

The Bottom Line

There is conflicting research about whether melatonin is helpful or harmful to metabolic health, but some research suggests it may all come down to timing in relation to food consumption.

To keep your melatonin at ideal levels (and in turn benefit metabolic health), it may be worth your while to keep your dinners on the early side and avoid late-night snacking. Additionally, if you take melatonin supplements, a good practice is to space it out at least two hours after eating.

And when supplementing, as always, be mindful about the right dosage for you. Most research suggests that 0.3 to 0.5 mg is adequate, while many people regularly take between 5 and 10 mg — which could contribute to having negative effects.

This article was created in partnership with researchers at Base but Levels has no affiliate relationship and receives no compensation if you purchase products from Base. 

About Base

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