Soy-based formulas may cause early sexual maturity in baby girls’ genitalia, new research suggests.
Female infants given the non-dairy formula over cow’s milk alternatives or breast milk are significantly more likely to have mature cells in their vaginas, a study found.
Previous research suggests soy protein contains high amounts of the oestrogen-like compound genistein, which can alter people’s hormone levels and affect their development. It is unclear why boys appear to be less effected.
Lead author Dr. Margaret Adgent from Vanderbilt University, said: “Our study found subtle effects in oestrogen-responsive tissues in soy-fed infants and we don’t know if these differences are associated with long-term health effects.”
Past studies link soy to disrupted hormone function, leading to conditions such as infertility, breast cancer and thyroid disorders.
The researchers analysed 410 babies born in hospitals in Philadelphia between 2010 and 2013.
Some 102 of the infants were exclusively fed soy-based formulas, while 111 received cow’s milk alternatives and 70 were only given breast milk.
Stallings said: “All of the mothers had decided on their feeding preferences before we enrolled them in the study.”
The male baby participants were followed for 28 weeks and the girls for 36.
Signs of sexual maturation in the infants were assessed via analysing urethra volume; breast bud diameter; cells in the vagina and urethra; estradiol levels, which is a form of oestrogen; and follicle-stimulating hormone amounts, which is involved in egg production. Read more