Phytoestrogens

Anti-thyroid agents

We're sick of hearing that there are no harmful effects of  phytoestrogens.  Phytoestrogens disrupt thyroid function.

Theodore Kay of the Kyoto University Faculty of Medicine noted in 1988 that 'thyroid enlargement in rats and humans, especially children and women, fed with soybeans has been known for half a century'.

In fact, thyroid problems associated with soy were also well known to bird-breeders, which is how Soy Online Service first became aware of the goitrogenicity of soy.

Well known, but that fact seemed to escape manufacturers of the first commercially available soy formulas.  Those formulas were known to cause in goitre in infants and one can only wonder how many other infants were left hypothyroid or suffering from permanent thyroid damage by soy formulas.

The iodine levels in soy formulas were increased and instances of goitre in infants fed these products ceased.  However, there appears to have been no attempt to isolate or remove the goitrogenic properties from soy formulas.   This is of grave concern because, although elevated iodine levels would have helped to nullify the effects of the goitrogens, the goitrogens would still have been actively suppressing thyroid function in infants.  Hence millions of babies (particularly in the United States where soy formula feeding is most common) have needlessly been exposed to goitrogenic agents; Soy Online Service believe that infants fed soy formulas unnecessarily risk abnormal thyroid function and a greater risk of thyroid disease in later life.

So just what are these goitrogenic agents?  In 1997 research from the FDA's National Center for Toxicological Research (NCTR) showed that the darling of the soy industry, the isoflavone genistein, was a potent inhibitor of Thyroid Peroxidase (TPO); in fact genistein is a more powerful inhibitor of TPO than common anti-thyroid drugs!  If genistein could inhibit TPO in vitro, it follows that it could result in an elevation of Thyroid Stimulating Hormone (TSH), and a subsequent decrease in thyroxine (T3) in vitro; in other words consumption of the soy isoflavone genistein might result in hypothyroidism and goitre.

Recent research leaves little doubt that dietary isoflavones in soy have a profound effect on thyroid function in humans. A study by Japanese researchers concluded that intake of soy by healthy adults for a long duration caused enlargement of the thyroid and suppressed thyroid function. These researchers studied the effects of feeding 30 g of soybeans per day on thyroid function and found that after one month there was a significant increase in thyroid stimulating hormone (TSH) levels in a group of 20 adults (group I) but no change in thyroxine levels.

Diffuse goitre and hypothyroidism appeared in some of these subjects and about half of another group of 17 adults (group II) that took soybeans for 3 months. This group also had increased TSH levels, especially in older subjects, but once again there was no significant change in plasma thyroxine. After three months of soy intake other relevant symptoms included constipation (in 53% of subjects), fatigue (in 53% of subjects), lethargy (in 41% of subjects). It should be noted that iodine intake (via seaweed) was normal in all subjects.

The goitre was a diffuse goitre (degrees I and II enlargement) and occurred in 3 of group 1 and 8 (47%) of group 2. One subject in group 1 developed sub-acute thyroiditis. Two of the 11 subjects with goitre showed no reduction in goitre size one month after cessation of soy but goitre size was reduced in the other 9 subjects. The two subjects received thyroxine treatment and their goiters reduced in size after two and six months respectively.

The combination of a moderately elevated TSH with a normal free thyroxine defines subclinical hypothyroidism, a condition which may evolve towards overt hypothyroidism especially in persons with anti-thyroid antibodies. The condition is defined as the state in which a reduction in thyroid hormone secretion is compensated for by an increased TSH production to order maintain a clinically euthyroid status. Subclinical hypothyroidism is of increasing importance and its prevalence appears to be growing such that studies to define both its evolution and strategies for its management are warranted. Thyroid experts have noted that dietary factors may well play a major role in the development of this condition since high goitrogen intake can increase TSH secretion.

We have already noted that isoflavones bioaccumulate in infants fed soy formulas. Hence, there is strong evidence from both in vitro and in vivo studies that persistent TPO inhibition will occur in infants subjected to soy formulas long-term (for more than three months). The work of Ishizuki indicates that this persistent exposure to the anti-thyroid agents in soy will result in variable and elevated levels of TSH, even if iodine levels are sufficient. There is a bounty of evidence showing that scenarios such as this can result in various thyroid diseases in humans.

Soy Online Service believe that it is utterly irresponsible for soy formula manufacturers to continue to place infants at risk of thyroid damage by refusing to remove isoflavones from their products.  Soy Online Service also believe that it is totally irresponsible and a sign of moral corruptness to promote anti-cancer benefits of soy without any inference that there may be other health risks (for example to the thyroid).

If you were fed a soy formula and suffer from a thyroid disorder, or have any reason to believe that soy may have caused you to develop a thyroid disorder, please contact us.

For really good information on the thyroid, visit Mary Shoman's thyroid website.

Read the testimonies of people who have suffered thyroid problems because of soy/isoflavone supplements and the shocking results of Larrian Gillespie's "self as a guinea-pig" experiment.