Melatonin supplementation may support repair of oxidative DNA damage in shift workers. Digest
Melatonin is best known for regulating sleep timing, but it also has strong antioxidant properties that may support DNA repair. Since night shift work can suppress normal melatonin secretion and has been linked to lower repair of oxidative DNA damage, researchers tested whether taking melatonin before daytime sleep could improve a DNA repair marker.
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The 4-week study included 40 night shift workers who were randomly assigned to take either 3 milligrams of melatonin or a placebo 1 hour before daytime sleep following a night shift. Urine was sampled after daytime sleep and during the following night shift, both before and near the end of the supplementation period. The researchers then measured two urine markers: a melatonin marker to confirm that the supplement raised melatonin levels, and 8-OH-dG, which they interpreted as a marker of oxidative DNA damage repair and cleanup. Sleep was tracked with a wrist-worn activity monitor, and participants rated how sleepy they felt during work.
- The supplement group had much higher levels of the melatonin marker in urine collected after daytime sleep (90.8 vs. 1.5 ng/mg) than the placebo group, but that difference had largely narrowed by the next night shift (3.3 vs. 1.3 ng/mg).
- Melatonin raised 8-OH-dG during daytime sleep by about 80% compared with placebo, but it fell just short of the study's threshold for a statistically clear result. During the following work period, 8-OH-dG showed no increase compared with placebo.
- When participants whose melatonin marker levels were low despite supplementation were excluded from the analysis, the daytime 8-OH-dG signal became stronger and reached statistical significance.
- Melatonin did not clearly improve sleep, making it less likely that the DNA repair signal was only a byproduct of better sleep.
Night shift work has been linked to higher cancer risk, and one proposed reason is that working at night can suppress or mistime the secretion of melatonin, a hormone that helps regulate the sleep-wake cycle and is involved in antioxidant defense. Oxidative stress can damage DNA and produce lesions such as 8-OH-dG. One way cells handle this lesion is to recognize the damaged piece, cut it out, and clear the removed material into urine. Melatonin could influence this pathway at two distinct points: upstream, by neutralizing reactive oxygen species and stimulating antioxidant enzymes, and downstream, by turning up genes in a DNA repair pathway that helps remove 8-OH-dG after it has formed. That is why higher urinary 8-OH-dG in this trial was interpreted as a sign of increased repair and cleanup of oxidative DNA damage.
The main limitation is that this was a small, short trial that focused on a single biomarker, so it cannot show whether melatonin improves long-term health in night shift workers. If larger, longer trials confirm the observed signal, melatonin could become a targeted way to support DNA damage cleanup in shift workers. In Q&A #54, I discuss melatonin's antioxidant properties and whether it has therapeutic potential beyond its role in promoting sleep.