Estrogens, and in particular estradiol, cause the body to assume a "feminine" shape: larger breasts and hips. They also increase blood supply to the skin and regulate the menstrual cycle. It is the monthly drop in estrogen levels that triggers the onset of menstruation. Estradiol also promotes vaginal lubrication and libido and a sudden rise in estradiol level triggers ovulation.
Estrogens also have an effect on the nervous system, increasing alertness. High levels of estrogen can lead to increased nervousness and emotional outbursts, which is why women often appear to be more “emotional” than men.
Unfortunately evidence also indicates that elevated levels of estrogen can enable the metastasis of cancer cells and thus spread them throughout the body.
Because estrogen has a suppressive effect on testosterone levels, and because estrogens tend to accumulate in fat cells, overweight men and women frequently end up with elevated levels of estrogen. This increases their risk of cancer and in men can also result in the partial loss of male characteristics such as deepness of voice, sexual responsiveness, and muscle mass.
Estrogen production plummets after menopause and some data suggests that this sudden decline increases women’s risk of developing Alzheimer’s Disease later on. Studies are underway in Europe to determine whether a regime of hormone supplementation that enables a gentle and gradual post-menopause decline in estrogen levels will have significant protective effects for women and reduce their risk of later developing neurodegenerative disease.