Exposure to soy-based formula in infancy and endocrinological and reproductive outcomes in young adulthood

Author: Strom BL, Schinnar R, Ziegler EE, Barnhart KT, Sammel MD, Macones GA, Stallings VA, Drulis JM, Nelson SE and Hanson SA
Publication: JAMA. 2001 Aug 15;286(7):807-14.

About 20% of babies in the US have been fed with soy based formula sometime during their first year of life. There are many anti-soy advocates and websites claiming that exposure of babies to soy based formula may cause reproductive problems later in live. These claims are mainly based on the fact that soy isoflavones bind to estrogen receptors and may influence hormone-dependent states. Soy based formulae contain indeed relatively high levels of isoflavones and may theoretically influence the development of the baby. These allegations may have a large effect on the population, denying them the access to a useful and alternative formula. The aim of this study was to examine the relationship between the exposure to babies of soy based formula and their health in young adulthood.

This study was a carried out in adults aged between 20 and 34 year who participated as baby in a controlled feeding study at the University of Iowa. About 1third was fed with soy formula and 2third with cow milk formula. The researchers mainly focussed on the reproductive health of the participants such as maturation, menstrual history, age of first ejaculation, age of voice change, number of days between periods and reproductive history, but also general health aspects.

The researchers found no statistically significant differences between the two groups in either women or men for 30 parameters. They only noticed a slightly longer menstrual bleeding duration and a greater discomfort with menstruation among women who were nursed as baby with soy based formula. They concluded that exposure of babies to soy based formula does not appear to result in health or reproductive problems later in live.