What do the following have in common:
They are all classified as goitrogens, or foods that have been shown to trigger goiter, or thyroid gland enlargement. Most of them do this either by blocking iodine uptake in the thyroid gland or by blocking the enzyme, thyroid peroxidase. This effect can lead to reduction in thyroid hormone output by the thyroid gland, which then triggers increased thyroid stimulating hormone (TSH) by the pituitary; increased TSH acts as a growth factor on the thyroid, thus goiter.
Add to this list of goitrogens the flavonoid, quercertin, found in abundance in red wine, grapes, apples, capers, tomatoes, cherries, raspberries, teas, and onions. Most of us obtain around 30 mg per day from our diet. Quercetin, often touted as a healthy flavonoid alongside resveratrol (e.g., Yang JY et al 2008), has been shown to be associated with reduced risk for heart disease and cancer. Many people even take quercetin as a nutritional supplement.
Quercetin has also been identified as a goitrogen (Giuliani C et al 2008).
What to make of all this?
Most of these observations have been made in in vitro (“test tube”) preparations or in mice. Rabbits who consume a cabbage-only diet can develop goiter.
How about humans? The few trials conducted in humans have shown little or no effect. In most instances, the adverse effects of goitrogens have been eliminated with supplemental iodine. In other words, goitrogens seem to exert their ill thyroid effects when iodine deficiency is present. Restore iodine . . . no more goitrogens (with rare exceptions).
Should we as humans adopt a diet that avoids apples, grapes, tomatoes, red wine, tea, onions, soy etc. on the small chance that we will develop goiter?
I believe that we should avoid these common food-sourced goitrogens with as much enthusiasm as we should be worried about spontaneous combustion of humans or the appearance of vampires on our front porches. We are as likely to suffer low thyroid activity from quercetin or other “goitrogens” as we are to experience the “mitochondrial explosions” that are purported to set innocent people afire.
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