Estrogen (E) is 50 to 100 times higher in overweight menopausal women than in lean women, because fat cells also produce estrogen, and this probably explains the higher risk of breast cancer associated with overweight and female sex.
Excess weight and lack of exercise can lead to elevated insulin levels: insulin resistance is the consequence. Then chronically elevated insulin increases estrogen: in particular, estrone worsens insulin resistance. Thus a vicious cycle is established: increased insulin creates increased estrogen, which can lead to increased insulin and insulin resistance, which tends to increase weight, which leads to more estrogen production.
This is a downward spiral that seems to have no end.
Estrogen levels, however, vary according to the state of menopause. Before menopause, women produce estrogen mainly in the ovaries, although fat cells continue to produce it. After menopause, women produce estrogen mainly in the adipose tissues. Overweight or obese women having many more fat cells produce more estrogen.
Before menopause, overweight women have lower estrogen production than women of normal weight, as overweight premenopausal women are more prone to ovulate irregularly, resulting in lower levels of circulating estrogen. In contrast, the opposite happens after menopause: overweight women consistently have higher estrogen levels. Add to this the fact that excess fat after menopause produces estrogen from testosterone by a process called aromatization: the enzyme involved is called aromatase. Obesity lowers sex hormone binding globulin (SHBG) thereby increasing free estrogen in the blood.
Weight gain is also related to endometrial cancer, another consequence of estrogen overload: in fact, 40% of women with endometrial cancer are obese.
Increased estrogen in postmenopause is also a risk factor for breast cancer.
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