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Physical Activity Increases Production of Hormone Believed to Protect Against Breast Cancer

Toronto, ON - December 1, 2005:  Moderate physical activity, which is believed to help reduce the risk of breast cancer, may do so because it increases production of a hormone believed to have protective effects against the disease, a Canadian research team has learned.

Researchers at Mount Sinai Hospital 's Samuel Lunenfeld Research Institute in Toronto have completed a study of how light and other factors, such as physical activity, influence the production of melatonin - a hormone released mainly at night in the absence of light and believed to protect against breast cancer. The findings of the study have been published in the December 1, 2005 edition of the American Journal of Epidemiology PDF Icon

The study is among the first to demonstrate the role of physical activity in potentially modifying melatonin levels, thus creating biological evidence for a reduced risk of breast cancer among women who exercise regularly.

"If we know that increased melatonin production could be an underlying reason for the protective effects of physical activity against breast cancer, then there is great opportunity for the scientific community to build on this knowledge and help women understand what steps they can take to reduce their risk of developing the disease," said Dr. Julia Knight, the study's lead investigator at the Samuel Lunenfeld Research Institute at Mount Sinai Hospital and a University of Toronto professor in the Department of Public Health Sciences.

The study, funded through the Canadian Breast Cancer Research Alliance with special funding from the Canadian Breast Cancer Foundation - Ontario Chapter to study the modifiable risk factors for breast cancer, took place between 2002 and 2004 and involved the participation of 213 female volunteers whose melatonin levels were monitored over time.

"Our focus on primary prevention research was initiated with the long-term goal of building knowledge about how to stop breast cancer before it starts," said Sharon Wood, Executive Director of the Canadian Breast Cancer Foundation - Ontario Chapter. "We are encouraged by the findings of Dr. Knight's work, which could provide momentum for lifestyle changes that could lead to a healthier population and potentially reduce the incidence of breast cancer."

About the Canadian Breast Cancer Research Alliance
The Canadian Breast Cancer Research Alliance is the primary granting agency for breast cancer research in Canada . Since its inception in 1993, CBCRA has awarded $138 million to support 414 projects spanning the spectrum of breast cancer research, including prevention, early detection, treatment and care. CBCRA is a unique Canadian partnership of groups from the public, private and non-profit sectors committed to reducing the incidence of breast cancer, increasing survival, and enhancing the lives of those affected by the disease. CBCRA's members include: the Avon Flame Foundation, Canadian Breast Cancer Foundation, Canadian Breast Cancer Network, Canadian Cancer Society, Canadian Institutes of Health Research, Health Canada , the Public Health Agency of Canada, and the National Cancer Institute of Canada.

About the Canadian Breast Cancer Foundation

As the leading national volunteer-based organization dedicated to creating a future without breast cancer, the Canadian Breast Cancer Foundation works collaboratively to fund, support and advocate for relevant and innovative breast cancer research; meaningful education and awareness programs; early diagnosis and effective treatment; and a positive quality of life for those living with breast cancer. Since 1986, the Foundation has allocated millions of dollars to breast cancer research, projects and support services. It is supported by four regional Chapters: BC/Yukon, Prairies/NWT, Ontario, and Atlantic. Fundraising is done on a regional basis, with funds allocated for programs unique to the needs and priorities of each region.

About Mount Sinai Hospital
Mount Sinai Hospital is recognized nationally and internationally for its excellence in the provision of compassionate patient care, teaching and research. Its key priority programs are Women's and Infants' Health, Surgical Subspecialties and Oncology, Internal Medicine and Subspecialties, and the Samuel Lunenfeld Research Institute. It is a University of Toronto-affiliated patient care, teaching and research centre. Visit

About The Samuel Lunenfeld Research Institute
Established in 1985, the SLRI at Mount Sinai Hospital in Toronto is one of the world's leading centres for biomedical research. The Institute is part of Mount Sinai Hospital , an internationally recognized 440-bed acute care academic health centre affiliated with the University of Toronto . SLRI has 513 research, administrative and support staff, 100,000 square feet of laboratory space and a 25,000-square-foot pre-clinical research lab. For more information about SLRI research, visit

Media contacts:
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Fraser Lisa Marchitto
Canadian Breast Cancer Foundation - Ontario Chapter
416-815-1313 ext. 500