Iodine, Thyroid, & Cruciferous Vegetables

Thyroid disorders are more common as we age, especially hypothyroidism (low thyroid). Symptoms of hypothyroidism include fatigue, weight gain, dry skin, constipation, and sensitivity to temperature changes. Our bodies require iodine to make thyroid hormones and 70-80% of the iodine in the body is found in the thyroid gland. The rest is distributed through the body, in the ovaries, breasts, muscles, and blood.

Those at risk for low iodine intake include people who avoid iodized salt, dairy products, and seafood, and who do not regularly take an iodine-containing dietary supplement. An adequate intake of iodine for infants is 110-130 mcg/day; for children 1-8 years 90 mcg/day; children 9-13 years 120 mcg/day; and those 14 years and older 150 mcg/day.

The iodine content of plant foods (including vegetables, fruits, legumes) depends on the iodine content of the soil, which varies considerably. Seafood is rich in iodine because marine animals can concentrate the iodine from seawater. Seaweed (such as kelp, nori, kombu, and wakame) is also a rich source. Iodized salt provides about 70 mcg in ¼ tsp and 1 cup of plain lowfat yogurt or milk provides 55-75 mcg. (Please note that dairy milk substitutes cannot be assumed to contain iodine).

Iodine intake in the US (as measured by urinary iodine excretion) dropped by 50% between 1971-1974 and 1988-1994. “Much of this decline was a result of decreased levels of iodine in milk due to the reduced use of iodine-containing feed supplements and sanitizing agents in dairy industry, as well as the reduced use of iodate dough conditioners by commercial bakers.” Iodine intake in the US has remained stable since 2000. You can find additional information on iodine and the iodine content of food HERE.

Besides iodine intake, there are other factors that influence iodine utilization or thyroid hormone production. These include “goitrogens” present in some foods, most commonly the cruciferous vegetables (cabbage family), which include broccoli, Brussels sprouts, cabbage, cauliflower, kale. The soybean isoflavones, genistein and daidzein, have also been found to inhibit the production of thyroid hormone. And tobacco smoking may be associated with an increased risk of goiter in iodine-deficient areas.

Goitrogens are not of clinical importance unless they are consumed in large amounts over time, along with a low-iodine intake. So please continue to enjoy cruciferous vegetables, because they provide so many health benefits, but go easy on kale juice unless your iodine intake is adequate. And you might also want to moderate your intake of isolated soy protein in protein powders, snack bars, and meal replacements. And, of course, stop or at least reduce smoking.

And speaking of cruciferous vegetables, enjoy the Crunchy Bok Choy Salad recipe from our Food for Thought—Healing Foods to Savor. This flavorful salad features colorful vegetables rich in protective compounds that support health. These include the carotenoid in the carrots, red bell pepper, and the green part of the bok choy. The bok choy, like all cruciferous vegetables, also contains sulfur-compounds that increase the activity of detoxification enzymes in the body.

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