June/July 2013 (vol. 10/1)

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Melatonin levels in nightworkers

Female nightshift healthcare workers experience lower levels of melatonin compared with their dayshift colleagues, but melatonin disruption – which has been suggested as increasing the risk of breast cancer in shift workers – is significantly less pronounced in Asian compared with white workers, this US study finds (n =276; 225 white and 51 Asian; aged 20–49). Nightshift workers worked at least 20 hours per week exclusively at night – at least eight hours per shift, finishing no earlier than 6am – and slept at night during their non-work days. Both white and Asian nightworkers had lower melatonin levels during daytime sleep relative to dayshift workers during normal night-time sleep (p < 0.0001). However, during non-work days white nightshift workers had a 47% reduction in melatonin levels during night-time sleep compared with day workers, whereas Asian nightworkers experienced only an 18% reduction (p = 0.01 for difference between Asian and white workers). Asian workers may be protected from the negative effects of shiftwork, conclude the authors.

American Journal of Epidemiology 2013; online first: doi: 10.1093/aje/kws278


Occupational Health at Work June/July 2013 (vol. 10/1) pp41