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Night shifts may hinder body’s ability to repair DNA damage

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Suppression of sleep hormone melatonin a likely factor, findings suggest

Night shift work may hinder the body’s ability to repair DNA damage caused by normal cellular processes, suggests a small study published online in Occupational & Environmental Medicine.Night shifts may hinder body's ability to repair DNA damage

Previous research by the same authors of 223 night shift workers showed that day sleep was associated with lower levels in their urine of a chemical by-product of active DNA tissue repair called 8-OH-dG than night sleep — potentially indicating reduced capacity to repair cellular damage.

The findings led them to conclude that the key factor behind this observed difference was likely to be suppressed production of the ‘sleep hormone’ melatonin during day sleep relative to night sleep. Melatonin regulates the internal body clock also known as circadian rhythm.

In a bid to explore whether lower levels of 8-OH-dG might also be found in those working night shifts compared with those getting a normal night’s sleep, they measured 8-OH-dG levels in the stored urine samples of 50 night shift workers from the previous study.


These 50 people had exhibited the widest discrepancies in levels of circulating melatonin between night work and night sleep.

Analysis of the urine samples showed that melatonin levels were much lower when taken during a night shift than when taken during a normal night’s sleep.

After taking account of potentially influential factors, such as alcohol consumption and shorter sleep duration (average 5.5 hours) during the day preceding a night shift, 8-OH-dG levels were only 20% of those observed during a normal night’s sleep (average 7.5 hours).

The 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. 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.

If such effects are confirmed, melatonin supplementation should be evaluated and explored for future study as an intervention to reduce the occurrence of potentially carcinogenic DNA damage among shift workers.