Persistent hypothyroidism in an infant receiving a soy formula: case report and review of the literature.

Abstract

Soy-induced goiter was a well-known phenomenon before 1966, the back date used in many computerized literature databases.1-4 In the mid-1960s, iodine-supplemented infant soy formulas prepared from isolated soy protein were introduced by commercial manufacturers.5 Since then, there have not been any documented cases of soy formula-associated hypothyroidism. We present the case of a patient with congenital hypothyroidism who remained persistently hypothyroid while on a soy formula diet despite large doses of L-thyroxine (T4). This case made us reaware of the historical data on the effects of soy on thyroid function. It also realerted us to the thoughtful use of formula preparations and close dietary monitoring of hypothyroid infants.