Oestrogen is the principal female sex hormone, found predominantly in women. Oestrogen is also present, to a lesser degree, in men. The primary male sex hormone, testosterone, regulates sexual development in menthe growth of the sexual organs--as well as secondary sexual development such as development of the characteristic male musculature, body hair, bone mass and vocal tone. When male oestrogen levels are increased there can be uncharacteristic developmental and physiological changes.
Men take oestrogen for a number of reasons. Trans-gender males use the hormone to effect the changes in their bodies that will make them appear more feminine.
According to the Prostate Cancer Foundation, the use of synthetic forms of oestrogen can counteract the effects of testosterone, which fuels the growth of prostate cancer, and slow the growth of the tumour. The findings of a recent research study, presented by lead author Ourania Kosti, Ph.D., of the Georgetown Lombardi Comprehensive Cancer Center, which were presented to the American Association of Cancer Research on April 18, 2010, indicated some positive correlation between certain oestrogen and effective treatment of prostate cancer.
In the Aug. 1, 2003 issue of "The Journal of Clinical Endocrinology & Metabolism," a research team from the Johns Hopkins School of Medicine led by E. Moore stated that compounds that mimic the effects of oestrogen, known as phytoestrogens, can be found in some health food supplements. Phytoestrogens can be found in many foods, although their presence in soy products was mentioned specifically in the study. It is unclear what effect, if any, phytoestrogens have on male testosterone and oestrogen levels, although according to the 2003 Johns Hopkins study some decrease in the male sex hormone and corresponding increase in female hormone levels has been reported in previous research.
In the May 2009 issue of "Environmental Perspectives," a research study conducted by U.K. universities and led by Dr. Susan Jobling of Brunel University examined the link between the pollution of watercourses by chemicals--some of which block the effects of the male hormone testosterone-- and the feminisation of fish in those watercourses. According to the study the affected fish had their breeding capability reduced and, in some cases, male fish actually changed gender to female. The research suggested that there may be the potential for human male fertility to be negatively affected by the same water borne pollutants, some of which are contained in medicines for cancer treatment as well as other pharmaceutical treatments and pesticidies.
The feminising effects of oestrogen on the male body can be considerable if taken in large enough doses. The growth of breast tissue, tenderness around the breast, enlargement of the nipple, softening of the skin and a reduction in the size of the testes are all effects that may be observed. Oestrogen intake can also reduce the incidence and growth of facial hair and promote a more feminised body shape. In cases where testosterone levels are already low, smaller amounts of oestrogen can have visible effects too.
Aside from its feminising effects, high levels of oestrogen--as associated with the larger dose, regularly administered oestrogen therapies undertaken by transgender patients and those fighting prostate cancer--can also have more serious consequences. As noted by the 2003 Johns Hopkins study, more serious side effects may include increased susceptibility to sickness and disease, a greater chance of blood clots, pulmonary embolism, strokes and liver disease. Personality and mood may also be negatively impacted.
For those undertaking hormone therapies for the purpose of gender reassignment, physiological changes are to be expected. In other instances the visible changes detailed in this article may or may not be attributable to oestrogen. Diet, genetic factors and general health can all be contributory factors, and to establish the true cause of any irregularity a consultation with a primary physician is required.