1. Lifestyle is a very important way to reduce breast cancer risk.
The International Agency for Research on Cancer estimates that 25% of breast cancer cases worldwide are due to overweight/obesity and a sedentary lifestyle.
https://www.ncbi.nlm.nih.gov/pubmed/12897329
“Dietary factors are estimated to account for approximately 30% of cancers in industrialized countries, making diet second only to tobacco as a preventable cause of cancer.” (“Diet, nutrition and the prevention of chronic diseases,” World Health Organization Technical Report Series, No. 916)
http://www.who.int/dietphysicalactivity/publications/trs916/en/gsfao_cancer.pdf
2. Cigarette smoking increases the risk of dying from breast cancer
In January 2016, Michael Passarelli and colleagues from the University of California, San Francisco and other institutions published a study in the Journal of Clinical Oncology about how smoking before and after a breast cancer diagnosis affects breast cancer survival. They found women who smoked one year before their breast cancer diagnosis were more likely to die of breast cancer than women who never smoked. And women who quit smoking after their breast cancer diagnosis were less likely to die from breast cancer than women who continued to smoke after diagnosis.
https://www.facingourrisk.org/XRAYS/smoking-before-or-after-breast-cancer
In another study, women who did not smoke, but whose husbands smoked, had nearly 50% more risk of breast cancer.
http://onlinelibrary.wiley.com/doi/10.1111/cas.12619/full
In yet another study, researchers found that women between 20 and 44 years old who had smoked a pack of cigarettes per day for at least 10 years were 60 percent more likely than those who smoked less to develop a common type of breast cancer.
http://www.reuters.com/article/us-health-smoking-breast-cancer-idUSBREA190CZ20140210
3. Exercise can reduce breast cancer risk
An increase in physical activity is linked to lower breast cancer risk. The difference in risk between the most active and the least active women is typically around 25%.
http://www.cancer.org/cancer/news/features/get-moving-to-help-reduce-your-risk-of-breast-cancer
