Breast Cancer Risk Linked To Sleep Patterns

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Breast Cancer Risk

Linked To Sleep Patterns

By Andre Picard

The Globe and Mail

7-20-5

 

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.

 

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.

 

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. "

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

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.

 

Dr. Schernhammer said the results suggest that the melatonin is

influencing risk, not the shift work itself.

 

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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