U.K. Government Reports on Soy Phytoestrogens 39897

U.K. Government Reports on Soy Phytoestrogens

LONDON--The U.K. Food Standards Authority's (FSA)Committee on Toxicity (COT) is currently consulting on a draft report outliningsoy phytoestrogens' impact on human health. The COT Working Group onPhytoestrogens was established in April 2000 to review the complex issuessurrounding phytoestrogens, including their link to fertility problems inanimals, and their benefits for heart disease and bone health. After reviewingthe available scientific evidence, COT prepared a report of its findings thatoutlines areas needing further research.

Key points that were investigated included whether soy-basedinfant formula posed a risk to infants; what the health implications of soyintake were for people in general; and, ultimately, if there are any benefitsderived from soy consumption. The group reviewed studies published up to April30, 2002. Although COT acknowledged there have been many anecdotal reports andreviews expressing opinions on phytoestrogens' health benefits, the group didnot consider these to be objective and did not include them in the review.

First, the group agreed on the definition of phytoestrogens: anyplant substance or metabolite that induces biological responses in vertebratesand can mimic or modulate the actions of endogenous estrogens, usually bybinding to estrogen receptors.

COT reviewed the science behind soy's phytoestrogens, ratherthan the whole soy compound. The group concluded that in vitro and in vivostudies have shown that phytoestrogens' primary biological effects are due tointeracting with estrogen receptors. However, much research in this field hasbeen on isoflavones, and comparatively little is known regarding prenylatedflavonoids, coumestrol or lignans--soy's other phytoestrogens.

In terms of soy-based formula, the researchers reported theconcentration of phytoestrogens found in these formulas is at a higher levelthan that found in human breast milk. It has been estimated that infantsdrinking these formulas consume 4 mg/kg of birth weight per day--which may behigher than any other population consumes.

Additionally, the group reported isoflavones inhibit thyroidperoxidase by lowering levels of free thyroxine (an iodine-containing hormone),but it is unknown if an infant with hypothyroidism could compensate for theselowered thyroxine levels. The group also acknowledged that, theoretically, ifthe thyroid status of an expectant mother is compromised, exposure to highlevels of phytoestrogens might impair normal fetal development.

The group recommended that soy-based formula should be given toinfants only for clinical reasons because of potential interactions betweenphytoestrogens and a developing thyroid.

In other populations at risk of certain health problems, thephytoestrogens' health benefits are inconclusive. Although it has been shownthat phytoestrogens lower the risk of developing breast cancer, some researchhas shown that these chemicals stimulate progression of the disease byproliferating the breast epithelium (a tissue layer) in premenopausal cancerpatients. COT suggested that until further research has shown a more conclusivebenefit linking soy with breast cancer, women with estrogen-dependent breastdisease should be cautious regarding their intake of phytoestrogen-rich food ordietary supplements.

In addition, the group reported no concrete benefits have beenshown between phytoestrogen intake and other cancers and menopause. However,they wrote that exposure to estrogens or phytoestrogens early in life may lowerthe risk of certain cancers by influencing the programming of an individual'shomeostasis. COT also reported there was considerable evidence linking soy withlowering low-density lipoprotein (LDL, or "bad") and totalcholesterol. In addition, short-term human studies and research using rat modelshave demonstrated that soy may protect the lumbar spine and prevent bone loss.

In the end, the group recommended that more long-term studiesare needed to better understand phytoestrogens' role in health. There is also aneed to investigate drug-phytoestrogen interactions, as well as phytoestrogens'biological effects beyond their role with regard to estrogen receptor sites.Additionally, the group suggested developing biomarkers of phytoestrogenexposure would aid epidemiological studies.

The consultation runs until Dec. 3, at which time FSA will beapprised of the science behind soy and the public's health. The comment periodis also open until Dec. 3; the report is scheduled to be presented to the FSA'sboard in February 2003.

The entire draft report can be found at www.foodstandards.gov.uk/multimedia/webpage/phytoreportworddocs.