Quercetin has a reactive enol built into it (at the name) which is probably responsible for its reported carcinogenic activity. Since non-natural Hormone Replacement Therapy (HRT) has recently been reported to be counterproductive to health, perhaps phytoestrogens should receive similar scientific scrutiny. All flavone and isoflavone structures seem to have some untoward effects upon the thyroid, for instance, but not all are carcinogenic. Furthermore, the monooxygenase in the thyroid is so compromised by a variety of environmental and dietary toxins, like the metal toxins sliding down the throat from dental work, that perhaps more aggressive digestion of thyroglobulin occurs, thereby increasing the sensitivity of the iodinating system.