Shift work and cancer

The effect of shift work on cancer, particularly breast cancer, has received increasing interest from the lay media since a panel of the International Agency for Research on Cancer declared in 2007 that “shift work that involves circadian disruption is probably carcinogenic to humans.”1 This conclusion was based on sufficient evidence from animal studies and limited evidence from human studies. The evidence is strongest for breast cancer, although the risk of prostate and colorectal cancer may also be increased by shift work. Recently, 38 women with breast cancer who had previously worked night shifts for at least 20 years were compensated by the Danish national board of industrial injuries.2 This has implications for employers, compensation boards, and employees internationally.

Two recent meta-analyses have suggested that the risk of breast cancer is increased by about 50% in night workers and by about 70% in flight personnel.3 4 If this association is true, shift work might have its effect by several different mechanisms …