Various Amounts of Weight Gain and Breast Cancer Risk

Several lifestyle factors play a significant role in determining an individual's risk of breast cancer. Many of them could be modified to protect against the malignancy. A nested case-control study was conducted to examine the association between selected lifestyle factors and non-BRCA-related breast cancer risk among French-Canadian women. Some 280 women with breast cancer and who were nongene carriers of mutated BRCA gene were recruited as cases. Another 280 women, without any cancer and nongene carriers of mutated BRCA gene served as controls. A tested lifestyle questionnaire was interviewer administered to incident cases to obtain information on weight history, smoking, physical activity, and other lifestyle risk factors. Odds ratios (ORs) and 95% confidence intervals (CIs) were estimated in logistic regression models. Comparing cases to controls, breast cancer risk was higher among subjects who reached their maximum body mass index (BMI) at an older age (>50 years) (OR=2.83; 95% CI: 2.34–2.91). A positive association was noted between breast cancer risk and weight gain of >34 lbs compared to weight gain of ≤15 lbs, since the age of 20 (OR=1.68; 95% CI: 1.10–2.58). Weight gain of >24 lbs compared to weight gain of ≤9 lbs, since the age of 30 also resulted in the same relationship (OR=1.96; 95% CI: 1.46–3.06). Similarly, since the age of 40, weight gain of >12 lbs compared to weight gain of ≤1 lb was associated with increased breast cancer risk (OR=1.91; 95% CI: 1.53–2.66). Women who smoked >9 pack-years of cigarettes had a 59% higher breast cancer risk (P=.05). Subjects who engaged in >24.8 metabolic-equivalent- (MET-) hours per week compared to ≤10.7 MET-hours per week of moderate physical activity had a 52% (P=.01) decreased risk and total physical activity between 16.2 and 33.2 MET-hours per week compared to ≤16.2 MET-hours per week, resulted in a 43% (P=.05) lower risk of breast cancer. In conclusion, weight history did affect breast cancer risk. Moreover, smoking appeared to raise the risk, whereas moderate physical activity had a protective effect.

From press release:

A recent study published in the Journal of Cancer Epidemiology has reinforced the correlation between being overweight, smoking and breast cancer. What makes this study unique is how test subjects were not diagnosed for BRCA1 and BRCA2 gene mutations, which predispose women to breast cancer.

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.