Isoflavones hormonal effects

In a 1996 review, the Committee of Toxicity of Chemicals in Food, Consumer Products and the Environment (COT) estimated the intake of isoflavones from soya-milk to be approximately 4 mg/kg/day over the first 4 months of life. This is greater than that associated with hormonal effects in premenopausal women, but the COT nonetheless supported the existing Department of Health s advice that... 

DUNCAN A M, MERZ B E, XU X, NAGEL T C, PHIPPS W R, KURZER M S (1999a) Soy isoflaVOneS exert modest hormonal effects in premenopausal women. J Clin Endocrinol Metab. 84 192-7. 

There have been some concerns expressed regarding the possible health consequences in adulthood (endocrinological and reproductive outcomes) of early-life isoflavone exposure from soy-based infant formula. The daily exposure of infants to isoflavones in soy-based infant formulas is 6- to 11-fold higher on a body weight basis than the dose that has hormonal effects in adults consuming soy foods. " However, evidence from adult and infant populations indicates that dietary isoflavones in soy-based infant formulas do not adversely affect human growth, development, or reproduction. 

Molteni, A., Brizo Molteni, L., and Persky, V. 1995. In vitro hormonal effects of soybean isoflavones. J. Nutr. 125 751S-756S. 

Duncan, AM. B.E. Merz X. Xu T.C. Nagel W.R. Phipps M.S. Kurzer. Soy isoflavones exert modest hormonal effects in premenopausal women./. Clin. Endocrinol Metab. 1999, 84, 192—197. Dyerberg, J. D.C. Eskesen P.W. Andersen A. Astrup B. Buemann J.H. Christensen P. Clausen B.F. Rasmussen E.B. Schmidt T. Tholstrup, et al. Effects of trans- and n-3 unsaturated fatty acids on cardiovascular risk markers in healthy males. An 8 weeks dietary intervention study. Eur. J. Clin. Nutr. 2004, 58, 1062-1070. 

ARJMANDI B H, BIRNBAUM R S, GOYAL N V, GETLINGE M J, JUMA S, ALEKEL D L, HASLER C M, DRUM M L, HOLLIS B w and KUKREJA s c (1998a), Bone-sparing effect of soy protein in ovarian hormone-deficient rats is related to its isoflavone content. Am J Clin Nutr. 68,1364S-68S. 

Diets rich in millet have been associated with endemic goiter in parts of West Africa where millet is a staple. The damage has been attributed to vitexin, a C-glycosyl flavone, that in rats has antithyroid activity and that in vitro inhibits thyroid peroxidase and the free radical iodination step in thyroid hormone biosynthesis. Isoflavones have produced similar antithyroid effects in rats, but clinical studies in adults have not. " However, this remains a possible concern in infants fed soya-based milk-replacers, especially if iodine supply is compromised. 

Structural similarity of the isoflavones to estrogen has been responsible for claims that they are natural alternatives to hormone replacement therapy (HRT). Soy isoflavones are not usually present in humans, unless caused by acute or chronic administration of soy products in the diet. If not in the diet, supplementation is required. One synthetic isoflavone, ipriflavone, has been shown to increase bone mass in postmenopausal women. The soy isoflavone daidzein makes up 10%o of the metabolites of ipriflavone, and it appears to be one of the metabolites that inhibit osteoclast activity in vitro. A number of studies have been reported on the effects of soy protein and genistein on bone density in rats, and it appears that it is the isoflavones that are responsible for the beneficial effects. Positive data from studies with cultured bone cells support a... 

These observations lead to the hypothesis that isoflavones may be biologically active, conferring health benefits that could explain the relatively low incidence of hormone-dependent diseases in countries where soy is a dietary staple. However, the effects of soy consumption on hormonal metabolism have been inconsistent, probably as a result of methodological differences in the studies as regards the characteristics of the subjects, study design, isoflavone form and other factors [7],... 

The evidence base for soy products having efiects on hormone-sensitive conditions is inconclusive. Soy products may reduce menopausal symptoms in postmenopausal women, although the current literature does not demonstrate effects of soy products on other hormone-sensitive conditions. However, importandy, clinical outcomes were not evaluated for most hormone-sensitive conditions. Conclusions are limited because of the relatively small numbers of studies and marked heterogeneity in design and in the profile of soy isoflavones across studies. 

Given the inconclusive evidence base for soy protein and isoflavones, many questions abound about whether specific soy products in adequate doses may have a health benefit. As noted in the AHRQ Report, further well-conducted studies are needed to determine whether soy protein or isoflavones affect hormone-related conditions. Numerous clinical trials are underway (www.clinicaltrials.gov) to evaluate effects of soy products on multiple clinical conditions including menopause, cancer, and bone health, among others. 

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