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Working night shifts may stop body from repairing DNA damage

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Working night shifts may hinder the body’s ability to repair DNA damage caused by normal cellular processes, according to findings from a new study.

Suppression of the hormone melatonin, which regulates a person’s “circadian rhythm” – also known as their ‘body clock’ - may have a role, said the US research, published in the Occupational and Environmental Medicine journal.

Melatonin boosts the activity of genes thought to be involved in the repair of DNA damage.

”Reduced melatonin production among shift workers during night work…likely reflects a reduced capacity to repair oxidative DNA damage”

Study on cell damage and night working

The same researchers previously studied the sleep of 223 night-shift workers. That investigation found sleeping in the day was associated with lower levels of a chemical by-product of active DNA tissue repair - called 8-OH-dG - than sleeping at night. This could mean that the body has a reduced capacity to repair cellular damage.

Researchers said the main reason for the lower levels of the chemical being associated with sleeping in the day was likely to be due to suppressed production of the sleep hormone melatonin.

The new research, led by Dr Parveen Bhatti from the Fred Hutchinson Cancer Research Center in Seattle, examined whether lower levels of 8-OH-dG might also be found in those working night shifts, compared with having a normal night’s sleep.

Researchers measured 8-OH-dG levels in the stored urine samples of 50 night-shift workers from the previous study.

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 – defined as an average length of 7.5 hours.

After taking account of factors that could influence melatonin levels, such as alcohol consumption and shorter sleep duration in the day before a night shift, 8-OH-dG levels were just 20% of the levels occurring during a normal night’s sleep, the research found.

“If such effects are confirmed, melatonin supplementation should be explored… to reduce the occurrence of potentially carcinogenic DNA damage”

Study on cell damage and night working

The researchers cautioned that because their research was an observational study, no firm conclusions could be drawn about cause and effect.

In addition, most of the people in the study were white, worked in healthcare, and of similar age, therefore making it difficulties to assume the findings were applicable more broadly.

Finally, the researchers were unable to collect data on the participants’ dietary patterns and “circulating antioxidant levels”, both of which could have affected their melatonin levels.

That said, the research indicated 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,” said the research paper, called Oxidative DNA damage during night shift work.

“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,” it 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,” said the paper.

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