New evidence has emerged to support claims that women who work nightshifts are more prone to develop breast cancer.
Research carried out in America found that women who regularly worked during the nights for up to three years were 45% more likely to develop breast cancer than those who did not work at night.
And the risk increased to 65% for those who regularly worked nightshifts for more than three years.
The results of the study, carried out in Seattle, suggest that bright light at night diminishes the body's supply of melatonin - a hormone involved in the control of the body's natural rhythms. This in turn may lead to an increase in levels of the female sex hormone oestrogen, which has been linked to breast cancer.
The results of the latest study were based on the work history of 822 women with breast cancer and 671 without. Scott Davis, an epidemiologist at the Fred Hutchinson Cancer Research Center in Seattle the latest study was carried out, said: "The numbers in our study are small, but they are statistically significant."