Overweight and obese women — defined as having a BMI (body mass index) over 25 — have a higher risk of being diagnosed with breast cancer compared to women who maintain a healthy weight, especially after menopause. Being overweight also can increase the risk of the breast cancer coming back (recurrence) in women who have had the disease. This higher risk is because fat cells make estrogen; extra fat cells mean more estrogen in the body, and estrogen can make hormone-receptor-positive breast cancers develop and grow
Eating Unhealthy Food
Diet is thought to be partly responsible for about 30% to 40% of all cancers. No food or diet can prevent you from getting breast cancer. But some foods can make your body the healthiest it can be and help keep your risk for breast cancer as low as possible. Research has shown that getting nutrients from a variety of foods, especially fruits, vegetables, legumes, and whole grains, can make you feel your best and give your body the energy it needs. Eating food grown without pesticides may protect against unhealthy cell changes associated with pesticide use in animal studies.
Lack of Exercise
Research shows a link between exercising regularly at a moderate or intense level for 4 to 7 hours per week and a lower risk of breast cancer. Exercise consumes and controls blood sugar and limits blood levels of insulin growth factor, a hormone that can affect how breast cells grow and behave. People who exercise regularly tend to be healthier and are more likely to maintain a healthy weight.
Compared to women who don’t drink at all, women who have three alcoholic drinks per week have a 15% higher risk of breast cancer. Experts estimate that the risk of breast cancer goes up another 10% for each additional drink a woman regularly has each day. Research consistently shows that drinking alcohol can increase levels of estrogen and other hormones associated with hormone-receptor-positive breast cancer. Alcohol also may increase breast cancer risk by damaging DNA in cells
Smoking causes a number of diseases and is linked to a higher risk of breast cancer in younger, premenopausal women. Research also has shown that there may be link between very heavy second-hand smoke exposure and breast cancer risk in postmenopausal women.
Using Hormone Replacement Therapy
Because the female hormone estrogen stimulates breast cell growth, exposure to estrogen over long periods of time, without any breaks, can increase the risk of breast cancer. Taking combination (estrogen and progesterone) hormone replacement therapy (HRT) for several years or more, or taking estrogen alone for more than 10 years, are associated with increased breast cancer risk. (Combination HRT also increases the likelihood that the cancer may be found at a more advanced stage.)