Soy infant formula associated with high risk of fibroids in women

Women who were fed soy infant formula as babies are 25% more likely to develop uterine fibroids than those who were breastfed or given milk-based formula.

Researchers using a subset of data from a large US study examining environmental risk factors for cancer and other reproductive health outcomes looked at elements associated with the early development of uterine fibroids. Women who were fed soy formula as infants were 25% more likely to have been diagnosed with uterine fibroids by age 35 than women who had been breastfed or fed milk-based formula. Fibroids can cause pelvic pain, heavy menstrual bleeding, and are the leading cause of hysterectomy.

Soy-based foods contain naturally occurring estrogen-like components called isoflavones. Approximately 20% of the US infant formula market is composed of soy formula. Infants fed soy formula ingest relatively high levels of isoflavones. While soy foods make up a large part of Asian adults’ diets, Asian infants are either breastfed or receive very low amounts of soy. Isoflavone levels in US infants blood are 10 times higher than Japanese adults and 200 times higher than infants who are breastfed or fed cow’s milk-based formula.

Millions of female infants in the US are heavily exposed to high levels of isoflavones when consuming soy infant formula, placing them at increased risk for uterine fibroids and potentially other reproductive alterations. The study also found that not only was soy formula a risk factor for developing uterine fibroids but having a mother with prepregnancy diabetes, being born at least one month early, and growing up with low
socioeconomic conditions increased the development of fibroids in early adulthood.

To read the entire study, see:
D’Aloisio AA, Baird DD, DeRoo LA, Sandler DP. Association of intrauterine and early life exposures with diagnosis of uterine leiomyomata by age 35 in the sister study. Environmental Health Perspectives doi:10.1289/eph.0901423