CHICAGO, Aug 14, 2001 (United Press International via COMTEX) -- Researchers say interviews with young adults who received soy or cow milk formula as infants reveal little support for public concern about hormonal effects of phytoestrogens in soy brands, however long-term effects are unknown.

Soy infant formulas are given to about 20 percent of babies in the United States and recently have been blamed for certain adverse health effects, including disruption of the endocrine system and thyroid activity.

A new study, published in the Journal of the American Medical Association, finds little support for these concerns although certain aspects immediately were questioned by some infant nutrition authorities.

"We undertook the study because of accusations, largely in the lay press, about the potential dangers of soy formula," said Brian Strom, a co-author of the study and chair of the Department of Biostatistics and Epidemiology at the University of Pennsylvania.

The alleged problems with soy exposure concern the presence of soy isoflavones, phytoestrogens that act as a mild version of estrogen. Moderate amounts of soy isoflavones given to adults are purported, in some studies, to help prevent cancer. However, some experts believe very high doses may interfere with endocrine and thyroid function, especially in infants.

"It is one thing for an adult to have soy products as some part of their diet. When you give a baby soy formula, it is his or her entire diet," said Carol Huotari, manager of the Center for Breastfeeding Information at La Leche League in Schaumburg, Illinois.

Strom and his colleagues undertook a retrospective study of a number of young adults, 20 to 34 years of age, who as infants had participated in feeding studies conducted at the University of Iowa between 1965 and 1978. The babies in these studies were given either soy-based formula or cow milk formula.

In telephone interviews, the researchers asked the young men and women about health outcomes that might potentially be related to estrogenic effects, such as endocrinological and reproductive problems. They reviewed data on self-reported pubertal maturation, menstrual and reproductive history, height and usual weight, and medical history, including a review of hormonal disorders.

The researchers concluded exposure to soy formula did not appear to produce different health or reproductive outcomes than exposure to cow milk formula.

"Of course, the study says nothing about the long-term effects of soy formula exposure, which can't be evaluated yet," Strom said. "If, say, vaginal cancer or some other cancers prove one day to be related to exposure, we wouldn't be able to tell that from this study. It is too soon to know."

Strom also acknowledged the researchers had not attempted to correlate the health outcomes with the particular kind of formula participants received. This was a limitation, he said, because the amount of soy isoflavones varies from product to product.

At least one finding stood out in the data: About 20 percent of young men and women exposed to soy formula as infants reported regular use of asthma or allergy medication as opposed to some 10 percent of those exposed to cow milk formula.

"Whether the exposure to soy formula produced that outcome or whether those people had underlying allergies as infants and so were put on soy formula, we have no way of knowing," Strom said.

Women who had been exposed to soy formula reported having slightly longer menstrual periods and greater discomfort with menstruation than those who had received cow milk formula. Women who had been exposed to soy formula also were slightly more likely to take weight control medication than those exposed to cow milk formulas. The significance of both of these findings is unknown.

Some authorities on infant nutrition dismissed the study's methodology. Of the 953 subjects in the original infant feeding studies, some were ineligible for the new study, others had been lost to follow up and others refused to be interviewed.

"We know nothing about the characteristics of the subjects lost to follow up or those who refused to be interviewed," said Dr. Naomi Baumslag, clinical professor of pediatrics at Georgetown Medical School. "That makes it difficult to draw conclusions about the effect or lack of effect of exposure to soy formula."

Baumslag also was critical the study concerned affluent white subjects and the findings about health outcomes cannot be applied to low-income family settings. The majority of minority mothers still rely on infant formulas. In fact, the largest purchaser of infant formulas in the country is a federal assistance program for poor families, Women Infants and Children.

Baumslag cautioned the study was partly financed by several manufacturers of infant formula. However, the National Institutes of Health also provided funding.

The debate over the possible risks of exposure to soy infant formula has taken place mostly in Great Britain and Canada.

"Only 1 percent of babies in the United Kingdom receive soy-based formula as opposed to 20 percent in the United States," Baumslag said. "Can medicine or babies really be that different in the two countries? It is hard to think that industry lobbying doesn't have a lot to do with the promotion of soy formula in this country."

Strom observed a certain percentage of pediatricians, for whatever reason, recommend soy formula to mothers who cannot or do not wish to breastfeed. "Of course, for the majority of women breastfeeding is preferred."

The rates for initiation of breastfeeding are climbing. According to widely cited data collected in hospitals by Ross Products Division of Abbot Laboratories, about 67 percent of new mothers breastfeed in the hospital while the rest choose to bottle-feed. In 1990, only about half of new moms breastfed their babies. That trend has been even more dramatic for black women. In 1990 about 23 percent of new black mothers breastfed but by 1999, the figure had jumped to 50 percent

　　From Healthy.net