Night shift workers who took 3 mg of melatonin an hour before daytime sleep showed 80 percent higher urinary levels of a key DNA repair marker than workers who took a placebo. The finding comes from a randomized, placebo-controlled trial of 40 workers published in the BMJ journal Occupational and Environmental Medicine in February 2025.
The marker in question is 8-hydroxy-2'-deoxyguanosine, or 8-OHdG. It appears in urine when the body clears out damaged fragments of DNA, so a higher level is read as more active repair, not more damage. The 80 percent increase seen in the melatonin group was borderline statistically significant, and the effect showed up during daytime sleep but not during the following night shifts.
Lead investigator Parveen Bhatti of the BC Cancer Research Institute and the University of British Columbia led the four-week trial with colleagues from Simon Fraser University and Duke University. All 40 participants were 18 to 50 years old, free of sleep disorders and chronic conditions, and had worked at least two consecutive night shifts a week, each lasting seven hours or more, for at least six months.
Why night work is on the cancer radar
Working through the night suppresses the body's natural melatonin, a hormone the pineal gland releases in darkness that helps regulate sleep and, in laboratory work, has been linked to antioxidant activity. Lower melatonin during shifts, combined with less recuperative daytime sleep, has been proposed as one pathway by which round-the-clock work could raise long-term disease risk.
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In 2019, an International Agency for Research on Cancer working group classified night shift work as probably carcinogenic to humans, its Group 2A category. That decision was based on sufficient evidence of cancer in animals and limited evidence from human studies, and it kept a classification the IARC first applied to circadian-disrupting shift work in 2007.
What the trial actually measured
The researchers wrote that their randomized placebo-controlled trial suggested melatonin supplementation may improve oxidative DNA damage repair capacity among night shift workers, and that increased oxidative DNA damage from weaker repair is a plausible mechanism behind the cancer link. They stressed that the study measured a repair biomarker, not cancer itself, and that their findings warrant future larger-scale studies that examine varying doses and longer-term impacts.
Two participants showed no rise in 8-OHdG at all. Bhatti told PsyPost that two people can take the exact same dose but end up with very different amounts circulating in their blood, one reason bigger trials are needed before any occupational recommendation could stand up.
Sleep duration and daytime alertness did not differ between the melatonin and placebo groups. Most participants in the trial worked in healthcare, and natural light exposure was not accounted for. The work was funded by the Canadian Cancer Society and the Canadian Institutes of Health Research.
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What it means for shift workers today
The result is a mechanistic hint, not a green light to self-prescribe. Melatonin is sold over the counter in the United States as a dietary supplement, but doses on store shelves vary widely and interactions with blood thinners, blood pressure medication and immunosuppressants have been documented. Anyone working nights who is considering a nightly pill should talk to a doctor about dose, timing and any prescription medications before starting.
The Bhatti group has said the next step is larger trials testing different doses and longer follow-up before melatonin can be recommended as a way to offset the DNA damage tied to shift work.
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This article is made and published by Jesper Bengtson, who may have used AI in the preparation.