Governments and employers worldwide are set to face pressure for compensation and changes to working patterns following research suggesting night shift work may cause cancer.

Cancer patients' groups, researchers and trade unions are studying evidence of the link after Denmark's National Injuries Board approved compensation of up to DKr1m ($181,000, €134,000, ￡123,000) for 38 women who developed breast cancer after working one or more nights a week for at least 20 years.

A review of recent studies by the International Agency for Research on Cancer concluded that night work disrupted the body's circadian rhythms, inhibiting the production of melatonin, a hormone important in fighting cancer. “Shift work that involves circadian disruption is probably carcinogenic to humans,” it concluded, putting the risk at the same level as chemicals containing lead, anabolic steroids, creosote, diesel exhaust and sun lamps.