Night shift workers who took melatonin supplements before sleeping during the day showed signs of improved DNA repair, according to a new randomized controlled trial published in Occupational & Environmental Medicine. The findings suggest that melatonin—a hormone involved in regulating sleep and circadian rhythms—could help counteract some of the biological stress caused by working at night, including the body’s reduced ability to fix oxidative DNA damage.
The study was led by distinguished scientist Parveen Bhatti and colleagues at the BC Cancer Research Institute, the University of British Columbia, Simon Fraser University, and Duke University. Their work builds on previous research showing that night shift workers have lower levels of melatonin and lower urinary concentrations of 8-hydroxy-2′-deoxyguanosine (8-OH-dG)—a marker that reflects the body’s ability to repair DNA damage caused by oxidative stress. Since cancer risk may be elevated when DNA repair is impaired, the researchers wanted to test whether supplementing melatonin could reverse that decline.
“When considering the millions of people worldwide who work night shifts, the associated negative health effects—including an increased risk of cancer—represent a significant public health concern,” explained Bhatti. “My research focuses on uncovering the underlying biological mechanisms through which night shift work impacts health.”
“By gaining a deeper understanding of these processes, we can develop more effective strategies to safeguard the long-term well-being of night shift workers. Through my earlier research, I observed that night shift workers weren’t as effectively repairing oxidative DNA damage, a type of DNA damage that contributes to occurrence of cancer, and this seemed to be tied to the low levels of melatonin they were producing.”
To investigate this, the researchers recruited 40 adults in the Vancouver area who worked night shifts. Participants had to meet several health and occupational criteria, including working at least two consecutive night shifts per week for at least six months. Individuals with chronic medical conditions or a history of melatonin use were excluded.
Participants were randomly assigned to one of two groups: one received melatonin supplements and the other received a placebo. Each participant took their assigned capsule one hour before going to sleep during the day after a night shift, continuing the routine for four weeks. The researchers collected data and biological samples both before and after the intervention to measure changes in sleep quality, fatigue, melatonin levels, and oxidative DNA damage.
To assess DNA repair capacity, the researchers collected urine from each participant during their day sleep and subsequent night shift, both before and during the intervention period. These urine samples were analyzed for 8-OH-dG levels, which increase when DNA damage is effectively identified and repaired. The samples were also tested for a compound called 6-sulfatoxymelatonin (aMT6s), a marker of circulating melatonin.
The researchers found that taking melatonin led to a borderline statistically significant increase in urinary 8-OH-dG levels during day sleep. On average, melatonin users had a 1.8-fold increase in 8-OH-dG excretion compared to those who took a placebo. This suggests a greater capacity for DNA repair during the daytime sleep period, when melatonin levels are normally suppressed by exposure to light. The effect was more pronounced when participants with low melatonin levels were excluded from the analysis, suggesting that individuals who absorb or respond to melatonin better may benefit more.
“The results of the study indicate that taking a melatonin supplement can improve oxidative DNA damage repair among night shift workers,” Bhatti told PsyPost.
However, no meaningful increase in 8-OH-dG was observed during the night shift itself. This might be because the melatonin taken before day sleep had largely worn off by the time participants returned to work, or because light exposure during the night shift suppressed natural melatonin production. Circulating melatonin levels did rise sharply after supplementation during day sleep, reaching supraphysiological levels in most participants, but these levels dropped significantly by the time participants were back on the job.
Sleep patterns were also monitored using wrist-worn actigraphs, and participants rated their sleepiness using a standard scale. Melatonin had no statistically significant effect on daytime sleep duration or on sleepiness during night work, although there was a small decrease in the time participants spent awake after initially falling asleep during the day. This finding suggests that melatonin may modestly improve sleep continuity during the day, but not enough to change how long people slept or how alert they felt during their next shift.
While the findings support the idea that melatonin can improve oxidative DNA damage repair during daytime sleep, the authors caution that their study had some limitations. The sample size was small, and most participants worked in healthcare or social assistance roles, which may limit how broadly the results apply. The study also did not control for participants’ light exposure or other potential influences on melatonin production, nor did it assess long-term outcomes.
“We conducted a small-scale, short-term trial,” Bhatti noted. “There is a lot more research that needs to be done before we can recommend that night shift workers take melatonin supplements to reduce their risk of developing cancer.”
The researchers also pointed out that the effect of melatonin was highly variable between individuals. While most people in the melatonin group saw large increases in circulating melatonin levels during day sleep, a few did not—suggesting that absorption or metabolism may differ from person to person. When those with the lowest measured melatonin levels were excluded, the increase in 8-OH-dG excretion became statistically significant, indicating that individual biology plays a role in how well melatonin works.
“A key issue with melatonin supplements is that there is a lot of variation between people in the amount of melatonin that actually gets into their circulation,” Bhatti explained. “Two people can take the exact same dose of melatonin but then end up with very different amounts circulating in their blood. So, depending on the dose that is given, some night shift workers may not experience any benefit.”
Although melatonin is widely available and often used for sleep issues, very few trials have looked at its potential for protecting against long-term health risks associated with night shift work. This study is among the first to directly test whether melatonin can counteract a specific biological pathway involved in cancer development.
“The findings of the study were quite compelling, but we need much larger-scale studies with longer follow-up periods to determine the efficacy of melatonin supplementation,” Bhatti said. “In addition, future studies should evaluate multiple different doses of melatonin; we only evaluated the impacts of a 3 mg dose.”
The study, “Melatonin supplementation and oxidative DNA damage repair capacity among night shift workers: a randomised placebo-controlled trial,” was authored by Umaimah Zanif, Agnes S. Lai, Jaclyn Parks, Aina Roenningen, Christopher B. McLeod, Najib Ayas, Xiangtian Wang, Yan Lin, Junfeng (Jim) Zhang, and Parveen Bhatti.
