Shift work is hard on the body. It's a schedule that reprograms the biological clock every few days. Those adjustments can disturb sleep patterns, impair mental acuity, and foster
irritability. In fact, it might be even worse than that. Two new studies find evidence that women who work the graveyard shift also increase their chance of developing breast cancer.
Both reports, published in the Oct. 17 Journal of the National Cancer Institute, raise the prospect that the increased risk results from chronic suppression of melatonin. Concentrations of this brain hormone normally peak during darkness, usually around 1 a.m. Previous studies have indicated that in animals, nighttime lighting–which suppresses melatonin release–boosts the growth of cancers (SN: 10/17/98, p. 248: http://www.sciencenews.org/sn_arc98/10_17_98/19981017fob.asp.).