Cruciferous Vegetables, Iodine, And Thyroid Function
"Very high intakes of cruciferous vegetables, such as cabbage and turnips, have been found to cause hypothyroidism (insufficient thyroid hormone) in animals.The RDA for iodine for adults is 150mcg (150 micrograms/day). Seafood and sea vegetables (seaweeds like kelp) are good sources of iodine.
Two mechanisms have been identified to explain this effect:
Increased exposure to thiocyanate ions from cruciferous vegetable consumption or, more commonly, from cigarette smoking, does not appear to increase the risk of hypothyroidism unless accompanied by iodine deficiency. One study in humans found that the consumption of 150 g/day (5 oz/day) of cooked Brussels sprouts for four weeks had no adverse effects on thyroid function."
- The hydrolysis of some glucosinolates found in cruciferous vegetables (e.g., progoitrin) may yield a compound known as goitrin, which has been found to interfere with thyroid hormone synthesis.
- The hydrolysis of another class of glucosinolates, known as indole glucosinolates, results in the release of thiocyanate ions, which can compete with iodine for uptake by the thyroid gland.
So, if you eat a lot of cabbage, cole slaw, cauliflower, broccoli, Brussels sprouts, turnips, and the like, it would be a good idea to make sure you're getting 150 mcg of iodine a day, either through a supplement or sea foods. (If you use sea salt or other non-iodized salt, you need to be even more attentive. A 1/4 teaspoon of iodized salt, at 70 mcg, contributes about half of the day's requirements.)
DV = Daily Value. The Daily Value used here is 150 mcg. A food that provides 50% of the DV provides 75 mcg iodine.
According to the NIH Office of Dietary Supplements, dairy is a good source of iodine "due to the use of iodine feed supplements and iodophor sanitizing agents in the dairy industry."
I didn't know that cigarette smoking could lead to low thyroid function, assuming someone wasn't getting enough iodine. Is there something smoking doesn't affect?
This has me wondering. I eat a lot of cruciferous vegetables, and I also eat more salt than what is "recommended." There are probably a lot of factors involved in the salt cravings, but I wonder if they might be, partially, compensating for things.
It's probably quite a stretch, but I'll keep it in the back of my mind anyway.
I had been looking this up because someone had CT scans which use a lot of iodine and he was having side effects. Maybe cruciferous vegetables and soy (which also inhibits thyroid hormone synthesis) could help with a case of iodine overload?
Looks like you need to be careful with iodine supplementation:
Observational studies have found increased iodine intake to be associated with an increased incidence of thyroid papillary cancer. The reasons for this association are not clear. In populations that were previously iodine deficient, salt iodization programs have resulted in relative increases in thyroid papillary cancers and relative decreases in thyroid follicular cancers.
From Oregon State University:
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