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Do night shifts hinder body’s ability to repair DNA?

Lower melatonin production during night work might cut ability to repair normal DNA damage

Louise Prime

Wednesday, 28 June 2017

Circulating melatonin levels among shift workers during night work were much lower than during a normal night’s sleep and this might hinder their body’s ability to repair the DNA damage caused by normal cellular activity, researchers have reported* in Occupational & Environmental Medicine. They suggested that, if this effect is confirmed, future studies should evaluate melatonin supplementation as a means to restore oxidative DNA damage repair capacity among shift workers.

Researchers led from the Fred Hutchinson Cancer Research Center in Seattle, US, had previously shown that among 223 night shift workers, compared with night sleep, day sleep was associated with reduced urinary excretion of 8-hydroxydeoxyguanosine (8-OH-dG), a chemical by-product of active DNA tissue repair – potentially indicating a reduced capacity to repair cellular damage. They suggested that poor production of melatonin during day sleep relative to night sleep was probably the cause of this difference.

They set out to investigate this idea further in a new cross-sectional study, for which they selected 50 shift workers with the largest negative differences in night work versus night sleep circulating melatonin levels (measured as 6-sulfatoxymelatonin in urine), from among the 223 shift workers in their previous study.

When they analysed participants’ urine samples, they found that melatonin levels were much lower when taken during a night shift than when taken during a normal night’s sleep (mean 17.1ng/mg creatinine vs. 51.7ng/mg creatinine). They also reported that even after accounting for potential confounders, such as alcohol consumption and shorter sleep duration (average 5.5 hours) during the day preceding a night shift, 8-OH-dG levels during night work were only 20% of those observed during a normal night’s sleep (average 7.5 hours).

The study authors acknowledged possible factors that could have influenced their results, and said as theirs was an observational study they could draw no firm conclusions about cause and effect. Nevertheless, they concluded: “Our results indicate that, relative to night sleep, reduced melatonin production among shift workers during night work is associated with significantly reduced urinary excretion of 8-OH-dG.”

They said: “This likely reflects a reduced capacity to repair oxidative DNA damage due to insufficient levels of melatonin and may result in cells harbouring higher levels of DNA damage,” and added: “If such effects are confirmed, melatonin supplementation should be explored as an intervention to reduce the occurrence of potentially carcinogenic DNA damage among shift workers.”

* Bhatti P, Mirick DK, Randolph TW, et al. Oxidative DNA damage during night shift work. Occup Environ Med, published online first: 26 June 2017. doi: 10.1136/oemed-2017-104414

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