- One of the most effective ways to reduce the risk of
breast cancer may be to regularly get a good night's sleep -- in the dark.
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- A new study shows that women with the highest levels
of melatonin -- a hormone the body produces only when a person is sleeping
at night, in the dark -- have a breast cancer risk that is 40 per cent
lower than those with low levels of melatonin.
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- Dr. Eva Schernhammer, an epidemiologist at Brigham and
Women's Hospital in Boston, said the research suggests that "melatonin
secretion may play an important role in breast cancer development."
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- She said that when and how well a woman sleeps may also
influence whether she develops breast cancer, and that sleep patterns could
also have an impact on tumour development and, by extension, on the effectiveness
of treatment.
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- The research, published in today's edition of the Journal
of the National Cancer Institute, seems to confirm the long-held hypothesis
about the cause of sharply higher breast cancer rates among shift workers.
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- A number of studies have shown that workers who regularly
toil on the late-night shift, such as nurses, are about twice as likely
to develop breast cancer as those who work day shifts.
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- Disruption of melatonin production was long suspected
as the culprit, but it was only a theory, based on a retrospective look
at the work habits of cancer patients.
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- The new study by Dr. Schernhammer and a team at Harvard
University is different in that the researchers actually measured levels
of melatonin in the urine of women before and after they developed breast
cancer.
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- The research is an offshoot of the massive Harvard Nurses
Study, in which the health of almost 120,000 nurses has been tracked since
1989. As part of that project, more than 30,000 women have provided regular
urine samples.
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- The new study by Dr. Schernhammer focused on 147 women
who developed breast cancer; they were compared with 291 women of similar
background who did not develop it.
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- Melatonin production peaks at night, and exposure to
light at night interrupts production of the hormone. When this occurs,
it also stimulates a women's ovaries to produce extra estrogen; excess
production of the female sex hormone is a known risk for breast cancer.
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- The idea that too much exposure to light can raise a
woman's cancer risk derives from earlier research on blind women, who are
half as likely to develop breast cancer as sighted women. In blind women,
melatonin levels do not fluctuate and, as a result, their estrogen levels
are more stable.
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- In the new study, researchers found that melatonin levels
were sharply lower in women who developed breast cancer, even well before
their diagnosis. Among the 25 per cent of women with the lowest levels
of melatonin, 50 developed breast cancer; by comparison, among the 25 per
cent with the highest levels of melatonin, 23 developed breast cancer.
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- Dr. Schernhammer said the results suggest that the melatonin
is influencing risk, not the shift work itself.
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- This year, an estimated 21,600 women and 150 men will
be diagnosed with breast cancer, according to the Canadian Cancer Society,
and an estimated 5,300 women and 45 men will die of the disease.
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