Published in the Journal of Cancer Epidemiology, the study is unique because it did not include subjects who were diagnosed for BRCA1 and BRCA2 gene mutations, which predispose women to breast cancer.
The study entirely focused on lifestyle factors like smoking, exercise, nutrition and weight.
All women analysed 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," said lead researcher Vishnee Bissonauth, a graduate of the Universite de Montreal'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 increased the risk of breast cancer.
Where the weight gain was more than 15.5 kilos, the risk was found to increase by an average of 68 percent.
Risk increases depending on how late in life the weight gain occurs, according to the study.
Women who gained more than 10 kilos after age 30, or more than 5.5 kilos after age 40, were found to be almost twice as likely to suffer from breast cancer as a those whose weight was stable.
The study showed that the risk tripled if the body mass index was at its maximum after age 50.moking a pack a day for nine years was also found to increase breast cancer risks by 59 percent.
Though the impact of smoking seemed to decrease for menopausal women, it remained at 50 percent.
Bissonauth stressed the need for more research into the correlation between smoking and breast cancer.
The researchers revealed that moderate physical activity appeared to decrease cancer risks by 52 percent for pre-menopausal and post-menopausal women.
The correlation was also observed for women who did intense physical activity, but the difference was not significant, said the lead researcher.
That finding, said Bissonauth, may be down to the fact that women who did moderate physical activity were more likely to do it regularly, while those who did intense physical activity were likely to quit after a few weeks.
"Cancer is a complex disease and can be latent for several years. 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," said Bissonauth. (ANI)