Women who work night shifts are at higher risk of breast cancer, warn researchers.
Their findings suggest working at night increases the chances of the disease by 40 per cent.
Women working more than two night shifts a week have double the risk of those on day shifts, says a report from scientists, while night workers who also describe themselves as ‘morning people’ or ‘larks’ have a stronger risk than those who say they are ‘night owls’.
Experts believe a hormone in the body that potentially suppresses tumours may be disrupted by constant exposure to light during night-time hours.
There has been mounting evidence that night shifts might boost cancer risk because of the disruption to the body clock and hormone production.
The latest study, backed by the Danish Cancer Society, involved more than 18,500 women working for the Danish army between 1964 and 1999.
Researchers were able to contact 210 women out of a total of 218 who had breast cancer between 1990 and 2003 and who were still alive in 2005/06.