For the past few years, I’ve read about a number of studies pointing to an association between long-term night-shift work and breast cancer risk. We have been told that this relationship boils down to decreased melatonin secretion resulting from exposure to bright artificial lights during natural sleeping hours. It makes perfect sense to me, so I have not questioned the assertion. Night-time shifts are especially common in the medical field and especially among nurses, so these studies have always made me think about the nurses in my family with concern, but maybe I need not worry after all.
A new study out of the UK indicates there is no relationship between night-shift work and breast cancer risk. Researchers looked at data from 10 different studies from the UK, USA, China, Sweden and the Netherlands and found that the incidence of breast cancer was essentially the same whether someone did no night shift work at all or did night shift work for several decades.