People working night shift have reduced melatonin levels when they sleep. Bhatti and colleagues have now shown that this reduced melatonin leads to an impaired ability to repair DNA, allowing more damage to accumulate.

People working night shift must sleep during the day. However, our bodies have evolved circadian rhythms that rely on light signals to regulate sleep and other bodily functions via a hormone called melatonin. As a result, night shift workers often have problems with sleep and display altered melatonin levels, as their circadian rhythms are mismatched with their work schedules. Melatonin regulates the repair of DNA damage that is caused by oxidized molecules. Excess DNA damage can lead to faster ageing and an increased risk of cancer. Understanding how night shift work influences these mechanisms of repair could lead to treatments that lessen these negative effects.

Bhatti and colleagues published a study in Occupational and Environmental Medicine in which they investigated the effect of working night shift on DNA repair. The researchers’ sample consisted of 50 shift workers whose melatonin changed most dramatically when they were on night shifts versus day shifts, out of a larger group of 223 workers. Bhatti and colleagues then measured 8-OH-dG, a molecule that causes damage to DNA, in urine samples from these workers. When individuals with high melatonin levels sleep at night, 8-OH-dG should be excreted at very high levels, indicating that DNA repair is working well. None of the research participants were taking melatonin supplements and urine samples were collected from throughout working and sleeping periods. In addition to urine samples, Bhatti and colleagues used an actigraph to collect measures of sleep quality. The researchers then compared 8-OH-dG levels within each individual when they were on day shift (night sleep) and night shift (day sleep) schedules.

Individuals slept 7.5 hours on average when sleeping at night, versus 5.5 hours on average when sleeping during the day. When individuals were working the night shift, they excreted only 20% the 8-OH-dG levels that they excreted when they were working day shift. These differences were significant.

The reduced 8-OH-dG excretion in individuals working night shift suggests that DNA repair mechanisms are not working well, leading to the accumulation of damage to DNA. Unfortunately, Bhatti and colleagues did not have information on dietary intake, which may differ in individuals working night versus day shifts. More work will be needed to confirm these results and identify potential preventative treatments for shift workers.


Written By: C. I. Villamil


Reference: Bhatti et al. 2017. Oxidative DNA damage during night shift work. Occup Environ Med 0:1-4.

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