Soy Infant Formulas Get Clean Bill of Reproductive Health
Study Suggests Isoflavones in Soy Don't Cause Problems Later On
By Neil Osterweil
WebMD Medical News
Reviewed by Aman Shah, MD
Aug. 14, 2001 -- Parents may still have to worry about what their kids watch on TV or whom they're hanging out with, but they may be able to scratch off the list concerns about estrogen-like compounds in soy-based infant formulas. A study in the Aug. 15 issue of JAMA shows that the health status of adults who were fed soy-based formula as infants was similar to those who were fed cow milk-based formula.
Soy-based products contain varying amounts of isoflavones, which are chemically similar to estrogen. Because infants exposed to high levels of estrogen can have fertility problems later in life, some researchers have speculated that soy isoflavones, which are present in high doses in soy-based infant formulas, could also be harmful.
Researchers looked at 811 women and men aged 20-34 who, as infants, had been part of a formula study comparing soy- and cow milk-based formulas. The investigators, led by Brian L. Strom, MD, found no significant differences between the two groups in any of 30 different measures, including menstrual function, pregnancy outcomes, body size and weight, age at puberty, breast size, and other measures in women, as well as body size and weight and age at puberty in men.
The only differences they could detect were that women in the soy group reported slightly longer menstrual periods, but there were no differences in heaviness of menstrual flow. Soy-raised women also reported slightly more discomfort during menstruation. There were no differences between the milk- and soy-formula groups among men.
Strom, chair and professor of biostatistics and epidemiology at the University of Pennsylvania School of Medicine in Philadelphia, tells WebMD that the differences seen in the women were so slight that they could be accounted for by simple statistical variations rather than an actual biological effect of soy isoflavones.
"If this really was an estrogen effect, you would have expected to have seen it in some of the other outcomes as well, and you would also have expected to see not only periods longer by a trivial amount, but heavier periods," says Strom. "And you would have expected to see women to come to medical attention more. None of the things that would have gone with it came through."
"We also looked at cancer and didn't see a difference. But we're still looking at people who are relatively young, and their rates of cancer are sufficiently low that we weren't going to be able to get a definitive answer related to cancer," he says.
Janice M. Bahr, PhD, who studies the effect of phytoestrogens in animals, tells WebMD that concerns about the effects of phytoestrogens first arose when Australian ranchers noticed that female sheep that grazed on a type of clover high in isoflavones became infertile, and male sheep had difficulty urinating due to enlarged prostate glands.
However, people would have to eat diets that are much higher in soy than normal to get high enough levels of exposure, says Bahr. She is a professor of animal sciences, physiology, and molecular and integrative physiology at the University of Illinois at Champaign-Urbana.
"But there are now all these health food stores that are carrying isoflavone capsules," says Bahr. "No one really knows how much is in there ... but the levels can be quite high, so that people who are taking the isoflavone extract in a capsule or as a food additive could be ingesting very high levels of phytoestrogens."