Night shifts may hinder DNA repair

DNA repair may be reduced in people working at night time, compared with those having a good night's sleep, according to new research from the US.

The scientists found that levels of a byproduct of DNA repair, a molecule called 8-hydroxydeoxyguanosine (8-OH-dG) that is excreted in urine, were reduced by 80 per cent in night-shift workers. Samples from 50 shift workers were analysed, and the team compared levels of 8-OH-dG and the sleep-hormone melatonin in these samples with those collected during a night of sleep.

According to lead author Dr Parveen Bhatti of the Fred Hutchinson Cancer Research Center in Seattle, Washington, being awake at night-time affects the body's 'capacity to repair and clear oxidative DNA damage'. She added: 'Over time, this accumulation would likely increase the risk of cancer across multiple sites as has been observed among shift workers.'

A correlation between poorer health and shift work has been established in multiple studies, and scientists are trying to understand the mechanism behind it. Shift workers are known to be more likely to suffer from cancer, infertility, heart disease and diabetes.

Scientists had theorised that this was related to levels of melatonin – a sleep regulating hormone – which are higher at night but are lowered in people working at night. The new findings support, but do not prove this hypothesis.

Melatonin is known to increase activity in genes related to the Nuclear Excision Repair (NER) pathway, which is involved in repairing damage to DNA caused by the oxygen free radicals produced as part of normal processes inside our cells.

In a previous study of 223 shift workers, the same team had shown that much lower levels of 8-OH-dG were present in samples collected during sleep in daylight hours, than during sleep at night time, which also supports the theory.

The research was published in Occupational and Environmental Medicine.