Women who work the night shift may be at greater risk for breast cancer. Canadian researchers compared more than 1100 women with breast cancer to matched controls without cancer. About one-third of the women in each group had worked night shifts.
Statistical analysis showed that women who had worked at night for more than three decades were twice as likely to develop breast cancer as those with normal working hours or less nighttime work. This is not the first time overnight shifts have been linked to breast cancer in epidemiological studies. A proposed mechanism relates to melatonin suppression by bright lights at night. Melatonin is the body’s natural sleep hormone. When levels are too low, the body produces more estrogen, which may help explain the association with breast cancer.
The link between night shifts and a higher risk of breast cancer had been previously reported in nurses, but the women in the Canadian study had a much broader range of professions. This narrows the focus to shift work itself.
[BMJ, July 3, 2013]
