Excess bodyweight has also been shown to be a risk factor for breast cancer, because fat cells produce more estrogen. The lack of estrogen in women who have had both ovaries removed prior to the age of 40 makes them much less prone to breast cancer.
反觀 40 歲前因病切除兩側卵巢者，因缺乏雌激素，罹患乳癌的風險反倒大幅降低。