News Release

October 13, 2005

Embargoed until Wednesday, October 15, 12:01 a.m. EST

Contact: Patrick S. Keefe, 860-679-2447

Eight-Plus Hours Sleep Reduces Women’s Breast Cancer Risk

FARMINGTON, CONN. – Women who sleep longer than eight hours per night are at lower risk of breast cancer according to a new study by a University of Connecticut School of Medicine researcher.

The study, published October 15 in the journal Cancer Research, was based on a follow-up of 12,000 women for 20 years, and showed women who reported sleeping nine or more hours per night at the start of the follow-up, had about one third the risk of breast cancer over the next 20 years compared to women sleeping less.

The study was based on a larger theory of breast cancer which suggests that women’s exposure to light at night, leads to lowered melatonin levels which increase the risk of cancer. The study adds to the evidence that light at night is an important risk factor for breast cancer.

“This is very strong study,” said Richard Stevens, Ph.D., cancer epidemiologist, Department of Community Medicine and Health Care. “This was a large number of women, followed for a long period of time in Finland with excellent follow-up,” he said. “We assessed their sleep duration two times over the follow-up period, and we feel confident about the women’s exposure, and we’re sure about the outcome.”

The works builds on earlier work by Stevens which found increased risk of breast cancer in shift-working women, and lower risk in blind women. The study – Stevens collaborated with a Finnish research team from the National Public Health Institute in Helsinki – reveals that the longer a woman sleeps, the lower her risk of breast cancer. Women were asked twice, six years apart, how long they slept. The reduced breast cancer risk was strongest in those women who reported the same amount of sleep each time.

The result may be due to a longer dark period for long sleepers, and thereby less light at night.

“The study supported the prediction of the ‘Light at Night’ theory of breast cancer causation,” said Stevens. “The theory posits that if there is light at night, women are at risk; long sleepers get more dark and should be at lower risk.

“The results supported that hypothesis,” Stevens said.

Stevens said Finnish cultural and social norms made the study very high quality, and stronger than could be accomplished in most other places. Because of the country’s nationalized medicine and homogenous population, follow-up percentages were near 100 percent.

Dr. Stevens is available to talk about the study. Call Patrick Keefe, 860-679-2447 to arrange an interview.

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