Soy consumption reduces thyroid function and/or causes thyroid cancer
Some older studies of infants fed soy-based formula not fortified with iodine showed reduced thyroid functioning in those infants. Further research has shown that, in the absence of an iodine deficiency, soy does not reduce thyroid function. In relation to infants with congenital hypothyroidism, there is not yet complete consensus amongst the scientific community as to whether soy formula complicates this pre-existing condition. If you have an infant with congenital hypothyroidism, again, soliciting the advice of your doctor or health care provider would be a wise decision. As far as thyroid cancer is concerned, large population-based studies show that soy not only does not increase the risk of thyroid cancer, it exerts a protective effect.