Denmark is reported to be paying 40 women compensation after developing breast cancer. The women are being compensated because they were shift workers. It seems that women with a family history of breast cancer are not going to be compensated.

Is this going to be a precedent? How certain can we be that shift work is a carcinogen? There have been concerns for several years, but the problem is that prospective randomised trials to examine potential factors like this are difficult to do. One would need to be sure that it was the shift work, and not factors about the people doing shift work, or the unrelated habits that shift work might lead to, that were the cause. Retrospective studies can at best show an association, rather than causation. The International Agency for Research on Cancer – part of the World Health Organisation – says shift work is “probably” carcinogenic to humans, with “long-term nightworkers” having “a higher risk of breast cancer risk than women who do not work at night. These studies have involved mainly nurses and flight attendants…” 

There are plausible biological explanations – involving melatonin – and animal studies that would fit the thesis. But if we want more definite evidence, that means more research.