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Soy Infant Formulas Get Clean Bill of Reproductive Health

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WebMD Health News
Reviewed by Gary D. Vogin, MD

Aug. 14, 2001 -- Infants give parents a lot to worry about. But a study published in the Aug. 15 issue of the Journal of the American Medical Association suggests mom and dad might be able to scratch one thing off their concerns list: estrogen-like compounds in soy-based infant formulas.

Soy-based products contain varying amounts of substances known as isoflavones, which are chemically similar to the female hormone 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.

But in a survey of women and men who as infants had been part of a formula study, researchers from the University of Pennsylvania and University of Iowa found no significant differences in any of 30 different measures between those who had been raised on soy protein-based formula and those who had guzzled formulas based on cow's-milk proteins.

The researchers looked at menstrual function, pregnancy outcomes, body size and weight, age at puberty, breast size, and other measures in women, as well as body size, weight, and age at puberty in men. The only differences they could detect were that women who had been fed soy as babies reported having slightly longer menstrual periods than women who had been fed milk, 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.

Lead author Brian L. Strom, MD, 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 see 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, 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," Strom says.

The researchers also looked for differences in cancer rates between the two formula groups, but none were found. A possible explanation is that the study group is still relatively young (aged 20-34) and, therefore, participants are less likely to have developed cancer.

Janice M. Bahr, PhD, a scientist who studies the effect of plant-based estrogen-like compounds (called 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 found to be high in isoflavones became infertile, and that male sheep had difficulty urinating due to enlarged prostate glands, also from exposure to estrogen-like chemicals.

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