From: Misty 
Subject: SNET: Breast cancer linked with night shift work
Date: 5 Jan 2001 01:53:43 -0500
To: SNET , The Eagle Net ,
        Surfing the Apocalypse ,
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Breast cancer linked with night shift work
By Sarah Stock, Medical reporter
04jan01
http://theaustralian.com.au/common/story_page/0,4511,1576573%255E2702,00.htm
l

WOMEN who worked night shifts were one-and-a-half times more likely to
develop breast cancer than those who worked during the day, Danish
researchers have found.

Their study, which involved the medical and employment records of more than
7000 women aged 30-54 with breast cancer, found that the longer women
regularly worked at night, the higher the risk.
Published in the journal Epidemiology, the study does not conclude why night
shifts are linked to breast cancer but speculates it could be due to higher
alcohol consumption, a known risk factor, or exposure to artificial light.

Study author Johnni Hansen, of the Institute of Cancer Epidemiology in
Copenhagen, said artificial light suppressed production of the hormone
melatonin, normally produced in the body at night.

He said research had suggested low melatonin levels might stimulate the
growth of cancerous cells in the breast or encourage production of the
female sex hormone oestrogen, which has been widely linked to breast cancer.

Dr Hansen cites the experience of blind women, who have about half the risk
of contracting breast cancer as women with sight, to support the melatonin
theory: because blind women cannot sense light visually, it has no impact on
their melatonin production.

Australian Cancer Society chief Alan Coates said the melatonin link could be
true but more research was required. He said another possible cause of the
higher cancer risk was night workers' increased exposure to cigarette smoke.

Professor Coates said the risk of working night shifts was no higher than
that of taking the contraceptive pill. Women should not feel they needed to
change their working habits, he said, because breast cancer could not be
pinned down to a single cause.

NSW Breast Cancer Institute executive director Jon Boyages said the
conclusions needed to be tested in larger long-term projects such as the
Harvard Nurses Health Study, which involves more than 35,000 women.

"We cannot look at this study in isolation of other known risk factors,
including family history and hormonal factors," Professor Boyages said. "I
wouldn't get alarmed at all if I was a night-shift worker because of this
one study."



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