A Canadian study found that 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.

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 American Journal of Epidemiology.

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 Julia Knight, the study's lead investigator at the Samuel Lunenfeld Research Institute at Mount Sinai Hospital and at University of Toronto.

The study took place between 2002 and 2004 and involved the participation of 213 female volunteers whose melatonin levels were monitored over time.

Source: University of Toronto, 2005


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