A group of Italian specialists reported a case of clinically evident goiter and hypothyroidism observed in a child who, due to a cow’s milk allergy, was taking soy milk and following a diet aimed at reducing allergic reactivity.
Soy milks have been used extensively as an alternative to cow’s milk in children allergic to that food or in those with lactose intolerance. On the other hand, as early as the first half of the last century the discovery of a possible toxic effect of molecules contained in soy, called isoflavonoids and acting in the body as estrogens (phytoestrogens), had raised some concern about the use of soy milk in infants. Isoflavonoids have been shown to inhibit the activity of a thyroid enzyme called peroxidase, acting as alternative substrates for iodination mechanisms. Subsequent research had observed that this effect of isoflavonoids developed only in the presence of inadequate iodine intake. A systematic review of the literature, performed in 2007, had reported that modern soy milks with added iodine adequately supported growth and development, and in fact, no cases of goiter and hypothyroidism had been described with the introduction of this type of soy milk. Caprio and colleagues published a case report of a 22-month-old child who was prescribed a soy-based diet for a cow’s milk allergy and developed a clinically evident goiter and hypothyroidism. This was the first ever case of this type recorded in Italy and, to the authors’ knowledge, it is also the only case that has presented in countries where the Iodine Deficiency Disorders Control Program is active. The mother of the child in whom the problem occurred had hypothyroidism due to autoimmune thyroiditis, had delivered her son after a full-term pregnancy, with the child’s birth weight of 3,660 kg. At four months of age he had presented with intestinal inflammation due to dietary protein, and had since been on a diet, eliminating cow’s milk protein. For the first year of his life he had been given hydrolyzed infant formula and later soy milk. Weaning had never been completed, due to the parents’ fear of allergic reactions. Finally, the diet was low in salt and thus the introduction of iodine inadequate. At the age of 22 months, a goiter appeared and laboratory tests showed severe hypothyroidism. The child was given levothyroxine, and after three weeks thyroid function normalized and the size of the gland decreased. Thereafter, the dose of levothyroxine was gradually decreased until it was discontinued. In subsequent years, the child showed normal growth and a condition of euthyroidism.
In their conclusions, the authors pointed out that iodine added in the artificial milks used in children allergic to cow’s milk may not be sufficient to make up for the deficiency of this element, which must be administered separately.