Soy milk can be used as a milk replacement for people who are lactose-intolerant or who seek to increase their intake of soy protein. Like all soy products, soy milk has compounds that can mimic the effects of estrogen in the body and affect estrogen levels. It is not clear, however, that increased consumption of soy milk can have any effect on estrogen levels.
Phytoestrogens in Soy Milk
Foods and beverages made from soy contain chemicals called isoflavones. These chemicals have estrogen-like effects on the body, so they are often called phytoestrogens -- that is, estrogen that comes from plants. The isoflavones can bind to estrogen-responsive areas on cells in the reproductive organs, liver, brain and other tissues. Although these isoflavones can mimic the effects of estrogen, in some tissues the isoflavones block the effects of estrogen.
Potential Developmental Effects
Although soy milk is generally safe for adults, there is the possibility that its ability to either stimulate or block estrogenic signaling could have adverse effects. Young children and developing fetuses may be more vulnerable, due to the importance of estrogen regulation for development. Boys born to women following a vegetarian diet and eating more soy while pregnant may have an increased risk of hypospadias, a birth defect affecting affecting the location of the penis opening. Women fed soy formula as infants may also have longer menstrual bleeding and more menstrual discomfort. But there is no evidence that soy milk specifically affects development.
Effects on Cancer
The ability of isoflavones to affect estrogenic signaling could play a role in the development of cancers affected by estrogen levels, such as breast and uterine cancer. Increased intake of soy may help reduce the risk of both breast cancer and uterine cancer later in life. The effects of soy milk on cancer risk have not been studied, however.
Soy Milk and Hormones in Men
The effects of soy milk on hormone levels in men was studied in an article published in a 2001 issue of "Cancer Epidemiology, Biomarkers & Prevention." This study found that men who drank soy milk for eight weeks had lower levels of a form of estrogen called estrone than men who did not drink soy milk. This suggests that the isoflavones in soy milk may be able to lower estrogen levels. This decrease in estrone levels may help reduce the risk of prostate cancer, but more research needs to be done to see if decreases in estrone levels could affect prostate health.