The effect of soy phytoestrogen supplementation on thyroid status and cardiovascular risk markers in patients with subclinical hypothyroidism: a randomized, double-blind, crossover study.

Author(s): 

Sathyapalan T and Manuchehri AM and Thatcher NJ and Rigby AS and Chapman T and Kilpatrick ES and Atkin SL

Year Published: 

2011

Journal: 

The Journal of clinical endocrinology and metabolism

Category: 

Study Design: 

Abstract: 

CONTEXT: There is concern whether soy phytoestrogens may affect thyroid function. If true, soy phytoestrogens may be expected to have a greater impact in subjects with subclinical hypothyroidism. OBJECTIVE: The primary aim was to determine the effect of soy phytoestrogen supplementation on thyroid function, with a secondary aim of assessing the effects on cardiovascular risk indices in patients with subclinical hypothyroidism. DESIGN AND SETTING: We conducted a randomized, double-blind, crossover study in a tertiary care setting. PARTICIPANTS: Sixty patients with subclinical hypothyroidism participated in the study. INTERVENTION: Patients were randomly assigned to either low-dose phytoestrogen (30 g soy protein with 2 mg phytoestrogens, representative of a Western diet) or high-dose phytoestrogen (30 g soy protein with 16 mg phytoestrogens, representative of a vegetarian diet) supplementation for 8 wk, then crossed over after an 8-wk washout period. MAIN OUTCOME MEASURES: The primary outcome was progression to overt hypothyroidism, with secondary outcome measures of blood pressure, insulin resistance, lipids, and highly sensitive C-reactive protein (hsCRP). RESULTS: Six female patients in the study progressed into overt hypothyroidism with a standardized rate ratio of 3.6 (95% confidence interval, 1.9, 6.2) after 16-mg phytoestrogen supplementation. Both systolic and diastolic blood pressure decreased with 16 mg phytoestrogens, whereas systolic pressure alone decreased with 2 mg phytoestrogens. Insulin resistance (homeostasis model assessment of insulin resistance, 3.5 ± 0.09 vs. 2.6 ± 0.08; P