Obesity increases the risk for all types of estrogen receptor-positive breast cancers. Women who gain weight after menopause are most at risk. (On a positive note, losing weight after menopause decreases breast cancer risk.) In postmenopausal women, estrogen is produced in fat tissue. High amounts of fatty tissue increase levels of estrogen in the body, leading to faster growth of estrogen-sensitive cancers.
Estrogenis involved in building bone mass. Therefore, women with heavy, dense bones are likely to have higher estrogen levels and to be at greater risk for breast cancer.
Some studies have found a greater risk for breast cancer in taller women, possibly due to the higher estrogen levels associated with greater bone growth.