Women employees who work
night shifts are more likely to develop breast cancer than those who work in
the day, research has revealed.
Two separate studies, published
in the latest Journal of the National Cancer Institute, reveal a higher
incidence of breast cancer in women who regularly work night shifts.
The study focused exclusively
on women working between 7pm and 9am,
One study in Seattle finds that
women who have worked night shifts for three years or more are 60 per cent more
likely to develop breast cancer than those who work during the day.
A similar study in Boston shows
that nurses working a rotating night shift at least three times a month are
about 8 per cent more likely to develop breast cancer.
The report suggests that the
increased incidence was caused by changes in the body’s natural melatonin cycle
because of exposure to bright lights during darkness.
Melatonin production peaks at
around 1.30am and studies have shown that bright light reduces its secretion.
This may lead to an increase in oestrogen production, which has been linked to
Although there is no comparable
research in the UK, Nicola Hawe, science information officer at the Cancer
Research Campaign, said that several studies had indicated night shift work
could be linked to breast cancer.
Despite this, her advice to
night-working women is to stay calm and report any changes that occur.
"The reported increase in
risk is small and woman who work night shifts should not be unduly
alarmed," she said.