Breast Cancer: Risk Increases For Smokers And Overweight Women

Instead, women with such gene mutations were excluded to allow researchers to concentrate on lifestyle factors such as smoking, exercise, nutrition and weight. All women analyzed in the study were direct ancestors of the first French colonists.

"To our knowledge, this is the first study conducted on a sample of women without BRCA1 and BRCA2 gene mutations, which are often found in French-Canadian women," says lead researcher Vishnee Bissonauth, a graduate of the Université de Montréal's Department of Nutrition and a researcher at the Sainte-Justine University Hospital Research Center.

The study found that weight gains after the age of 20 increases the risk of breast cancer. If the weight gain is more than 15.5 kilos, the risk increases by an average of 68 percent. Risk increases depending on how late in life the weight gain occurs. A woman who gains more than 10 kilos after age 30 or more than 5.5 kilos after age 40 is almost twice as likely to suffer from breast cancer as a woman whose weight is stable. The risk triples if the body mass index is at its maximum after age 50.

The research team also found that smoking a pack a day for nine years increases breast cancer risks by 59 percent. The impact of smoking decreases for menopausal women but remains at 50 percent. According to Bissonauth, the correlation between smoking and breast cancer requires more research.

The investigation also found that moderate physical activity decreased cancer risks by 52 percent for pre-menopausal and post-menopausal women. The correlation is also observed for women who do intense physical activity but the difference isn't significant. This is because women who do moderate physical activity are more likely to do it regularly, while women who do intense physical activity are likely to quit after a few weeks.

"Cancer is a complex disease and can be latent for several years," says Bissonauth. "Therefore, it is important to work on the factors we can control and to lead a healthy lifestyle, which means watching one's weight, avoid smoking and doing regular exercise."

This study was funded by the Montreal Cancer Institute and the Fonds de la recherche en santé du Québec.