Melatonin does not affect the insulin resistance or the glucose tolerance of night shift workers, according to a new study from the University of Surrey and the University Medical Centre Hamburg. 

Melatonin treatment does, however, significantly improve the sleep quality of those working shifts.

In this study, published in Pharmacological Research, scientists explored how oral melatonin affects insulin resistance and blood pressure in night shift workers, who face a higher risk of Type 2 diabetes. Insulin resistance is when cells struggle to absorb glucose from the blood. 

Previous research suggests melatonin could help these workers’ glucose tolerance and heart health. This led scientists to investigate melatonin’s broader effects on the body.

“Night shift work is necessary for our emergency and health services and to keep our economy moving. However, working night shifts disrupt our circadian rhythms, which are driven by light/dark cycles and are associated with sleep disturbances, cardiometabolic diseases, and increased risk of diabetes,” says Debra Skene, PhD, professor of neuroendocrinology at the University of Surrey, in a release. “We need to find ways to limit the adverse health implications for night shift workers so they can continue in their roles whilst protecting their long-term health.”

To investigate the impact of melatonin, 24 night shift workers and 12 healthy non-shift workers were recruited and underwent glucose tolerance testing and blood pressure monitoring for 24 hours. Night shift workers were then randomized to receive oral melatonin (2 mg) or a placebo at night time or in the morning, depending on their shift schedule, for 12 weeks.

The authors identified that night shift workers were significantly more insulin-resistant than non-night shift workers. After 12 weeks of taking the hormone melatonin, no significant effect was observed in serum glucose or insulin concentrations, which are markers of insulin resistance. Similarly, for blood pressure, treatment with melatonin had no significant effect.

Unsurprisingly, researchers say, melatonin significantly improved the sleep quality of night shift workers. During the initial assessment, only 21% of night shift workers described their sleep quality as good; however, after 12 weeks of melatonin treatment, 50% of this cohort indicated good sleep quality. The proportion of good versus poor sleepers remained almost unchanged in the placebo group.

“The benefits of improved sleep for shift workers via melatonin are undeniable, and people should feel more rested and alert. However, since there is no evidence that the use of melatonin reduces insulin resistance, we need to find alternate ways to improve insulin resistance and lessen the likelihood of a person developing type 2 diabetes,” says Skene in a release.

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