The Effect of High Dose Isoflavone Supplementation on Serum Reverse T3 in Euthyroid Men With Type 2 Diabetes and Post-menopausal Women
Background
The health benefits of soy are widely reported but there are queries on the effect of soy isoflavones on thyroid function and the underlying mechanism of action.
Materials and Methods
We examined the effect of soy isoflavones on reverse tri-iodothyronine (or 3,3′,5′-tri-iodothyronine; rT3) in two studies comprising 400 patients: 200 men (study 1; 3 months) and 200 post-menopausal women (study 2; 6 months) who were randomized to consume 15 g soy protein with 66 mg of isoflavones (SPI) daily, or 15 g soy protein alone without isoflavones (SP) daily.
Results
SPI supplementation increased rT3 serum concentration in both men 0.41 (0.12) vs. 0.45 (0.14) nmol/L and women 0.33 (0.12) vs. 0.37 (0.09) nmol/L at 3 months compared to SP that was not seen at 6 months. Thyroid stimulating hormone (TSH) serum concentrations increased while free thyroxine (fT4) concentrations decreased with 3 months of SPI compared to SP supplementation for both men and women. rT3 correlated with TSH in both studies (p = 0.03) but not with either fT3 or fT4. fT3 levels did not differ between the SPI and SP preparations.
Conclusion
Soy isoflavones transiently increased rT3 levels within 3 months though reverted to baseline at 6 months. The mechanism for this would be either rT3 degrading deiodinase 1 and/or deiodinase 2 activities are transiently inhibited at 3 months, or inhibition of deiodinase 3, which generates rT3 from T4 is induced at 6 months. These changes were mirrored in the TSH concentrations, suggesting that short-term high dose isoflavone transiently impairs thyroid function in the first 3 months and may impact on general health during this period.
ISRCTN Registry: ISRCTN 90604927; ISRCTN34051237.
Other Information
Published in: Frontiers in Endocrinology
License: https://creativecommons.org/licenses/by/4.0/
See article on publisher's website: https://dx.doi.org/10.3389/fendo.2018.00698
Funding
Open Access funding provided by the Qatar National Library.
Food Standards Agency, United Kingdom (T01057 and T01060).
History
Language
- English
Publisher
FrontiersPublication Year
- 2018
License statement
This Item is licensed under the Creative Commons Attribution 4.0 International License.Institution affiliated with
- Weill Cornell Medicine - Qatar
- Sidra Medical and Research Center (2015-2017)
- Sidra Medicine
