Genistein (4′,5,7-trihydroxyflavone) is a phytoestrogen belonging to the class of soy isoflavones, a sub-class of flavonoids that have received great attention for their potential on human health benefits. The aim of this brief review is to summarize and better clarify the effects of genistein on human thyroid health. Recent studies suggest that genistein shows a good profile of safety on the thyroid although definitive conclusions have not reached. Goitrogenic effects were also noted in infants fed non-iodine-fortified, soy-based formula, a problem that was easily solved with iodine fortification. ![]() ![]() Much of the evidence for the goitrogenic effects of isoflavones is derived from experimental in vitro and in vivo studies. However, issues of potential harm on thyroid function resulting from soy isoflavones consumption have been raised. Genistein aglycone, one of the soy isoflavones, has been reported to be beneficial in the treatment of menopausal vasomotor symptoms, osteoporosis, and cardiovascular diseases, as well as in a variety of cancers. 5 Interdepartmental Program of Molecular and Clinical Endocrinology, and Women’s Endocrine Health, University Hospital of Messina, Messina, Italy.4 Master on Childhood, Adolescent and Women’s Endocrine Health, University of Messina, Messina, Italy.3 Section of Endocrinology, Department of Clinical and Experimental Medicine and Pharmacology, University of Messina, Messina, Italy.2 Section of Pharmacology, Department of Clinical and Experimental Medicine and Pharmacology, University of Messina, Messina, Italy.1 Section of Physiology and Human Nutrition, Department of Biochemical, Physiological and Nutritional Sciences, University of Messina, Messina, Italy.Adamo 1 †, Alessandra Bitto 2, Francesco Squadrito 2 and Salvatore Benvenga 3,4,5* Therefore, it is important for soy food consumers to make sure their intake of iodine is adequate.Herbert Marini 1 †, Francesca Polito 1 †, Elena B. In addition, there remains a theoretical concern based on in vitro and animal data that in individuals with compromised thyroid function and/or whose iodine intake is marginal soy foods may increase risk of developing clinical hypothyroidism. However, hypothyroid adults need not avoid soy foods. In contrast, some evidence suggests that soy foods, by inhibiting absorption, may increase the dose of thyroid hormone required by hypothyroid patients. Thus, collectively the findings provide little evidence that in euthyroid, iodine-replete individuals, soy foods, or isoflavones adversely affect thyroid function. With only one exception, either no effects or only very modest changes were noted in these trials. In total, 14 trials (thyroid function was not the primary health outcome in any trial) were identified in which the effects of soy foods or isoflavones on at least one measure of thyroid function was assessed in presumably healthy subjects eight involved women only, four involved men, and two both men and women. ![]() Thus, the purpose of this review is to evaluate the relevant literature and provide the clinician guidance for advising their patients about the effects of soy on thyroid function. One concern is that soy may adversely affect thyroid function and interfere with the absorption of synthetic thyroid hormone. However, despite the possible benefits concerns have been expressed that soy may be contraindicated for some subsets of the population. There are many bioactive soybean components that may contribute to the hypothesized health benefits of soy but most attention has focused on the isoflavones, which have both hormonal and nonhormonal properties. Soy foods are a traditional staple of Asian diets but because of their purported health benefits they have become popular in recent years among non-Asians, especially postmenopausal women.
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