Traditionally conceptualized as 'female hormones', oestrogens appear to have significant effects in the male biological system. Favorable effects have been noted on bone, brain and cardiovascular physiology while a potential role in the prostate pathology of the aging male has been seriously suspected. Oestrogens in male are predominantly the products of peripheral aromatization of testicular and adrenal androgens. While the testicular and adrenal production of androgens declines with aging, levels of total plasma oestradiol do not decline. This is to be ascribed to the common increase in fat mass with aging (the substrate of peripheral aromatization) and an increased aromatase activity with aging. But free or bioavailable oestrogens may decline due to an increase in sex hormone binding globulin.

Oestrogens produce significant beneficial effects on skeletal growth and bone maturation. In old age oestrogens are better predictors of bone fractures than androgens. Oestrogens exert effects on the brain: on cognitive function, co-ordination of movement, pain and affective state, and are maybe protective of Alzheimer's disease. Oestrogen effects on the cardiovascular system include those on lipid profiles, fat distribution, endocrine/paracrine factors produced by the vascular wall (such as endothelins, nitric oxide), blood platelets, inflammatory factors and coagulation.

The potentially adverse effects of oestrogens on the prostate may be due to a shift in the oestrogen / androgen ratio with aging.

Sources of estrogens in men are endogenous androgens, or in case of androgen deficiency, exogenous androgens. Dietary phytoestrogens or selective estrogen receptor modulators, as drugs, may be significant as well.