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Endocrine Abstracts (2015) 38 P439 | DOI: 10.1530/endoabs.38.P439

1Department of Academic Endocrinology, Diabetes and Metabolism, Hull York Medical School, University of Hull, Hull, UK; 2Department of Diabetes, Endocrinology and Metabolism, Hull and East Yorkshire Hospitals NHS Trust, Hull, UK; 3European Food Safety Authority, 43126 Parma, Italy; 4Department of Academic Cardiology, University of Hull, Hull, UK; 5Department of Clinical Biochemistry, Hull Royal Infirmary, Hull, UK; 6Weill Cornell Medical College, Doha, Qatar.

: In patients with subclinical hypothyroidism, soy protein and isoflavone combination has been shown to increase the risk of developing overt hypothyroidism; however, it is unclear if soy affects thyroid function in those without existing thyroid compromise.

Materials and methods: Two double blind randomised trials were undertaken in which thyroid function was performed routinely at the beginning and end as a secondary end point. In both trials soy protein 30g with and without 66mg of soy isoflavones were used (preparation 1); soy protein alone that was isoflavone free (less than 300 parts per billion following serial ethanol washing)(preparation 2) was used for a period of 12 weeks. Study 1: 200 women within two years of the onset of the menopause to determine the safety of soy on markers of bone turnover as the primary end point. Study 2: 200 men with T2DM with a total testosterone level ≤12 nmol/l with normal gonadotrophins with the primary end point of testosterone change. Here the secondary thyroid endpoints are presented.

Results: All patients had normal thyroid function at baseline in both the studies. In post menopausal women there was a significant increase in TSH (1.58±0.93 vs 2.57±1.19 mU/l; P value <0.01) and reduction of free thyroxine (1.08±0.17 vs 0.92±0.17 ng/dl; P value 0.02) after preparation 1 after 3 months compared to baseline. In men with type 2 diabetes there was a significant increase in TSH (1.82±0.10 vs 3.28±0.11 mU/l; P value <0.01) and reduction in fT4 (0.98±0.02 vs 0.86±0.02 ng/dl; P value <0.01) with preparation 1 but not after preparation 2 after 3 months compared to baseline. None of the patients developed subclinical or overt hypothyroidism during this period. There were no changes in fT3 after either preparation 1 or preparation 2. There was no significant change in TSH or thyroxine after supplementation of preparation 2.

Conclusions: There was a significant increase in TSH and reduction in free T4 only after soy protein with isoflavones suggesting a direct effect on the thyroid that is unlikely to be clinically significant unless thyroid compromise is already present. We have previously shown that isoflavone alone has no effect on thyroid function suggesting that the isoflavones in the soy protein matrix is active component.

Volume 38

Society for Endocrinology BES 2015

Edinburgh, UK
02 Nov 2015 - 04 Nov 2015

Society for Endocrinology 

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