Human physiological functions, including cell specialization, growth and development, depend on the thyroid -- a gland located in the neck. Thyroid stimulating hormones secreted by the pituitary gland stimulate the thyroid gland to produce two thyroid hormones: thyroxine and triiodothyronine. Because the thyroid hormones affect all the cells in the body, it is important to keep the thyroid healthy and functioning. Substances found in certain foods can affect the thyroid, causing it to either increase or decrease the amount of hormones produced.
Iodized Salt
The cells in the thyroid gland are the only cells in the body that can absorb iodine -- a trace mineral. In order to produce the thyroid hormones, the thyroid requires sufficient amounts of iodine. The National Institutes of Health Food and Nutrition Board recommends that adults intake 95 mcg of iodine per day. Failure to consume enough iodine affects thyroid function leading to hypothyroidism -- a condition of low levels of thyroid hormones. To support normal thyroid function and prevent other iodine deficiency disorders, the World Health Organization developed the Universal Salt Iodization program. Adding iodine to salt is an easy, cost-effective way to help the majority of people get enough iodine in their diet.
Cruciferous Vegetables
Cruciferous vegetables belong to the class of vegetables known as Brassica. This group of vegetables includes broccoli, Brussels sprouts, cabbage, cauliflower, collard greens, kale, kohlrabi, mustard, rutabaga, turnips, bok choy and Chinese cabbage. Although these vegetables contain many beneficial nutrients including folate, vitamin C, potassium and selenium, they also contain a substance known as goitrogens. Consuming large amounts of these vegetables can interfere with the production of thyroid hormones by competing with iodine uptake. This can lead to low levels of thyroid hormone, especially if you also fail to consume adequate levels of iodine.
Soy
Eating food products derived from the soybean may affect thyroid function. Soy food products contain isoflavones, compounds classified as phytoestrogen because they produce effects similar to the hormone, estrogen. Soy isoflavones may provide beneficial effects for certain hormone-associated cancers, such as breast cancer, but they may also interfere with the activity of the enzyme, thyroid peroxidase. Thyroid peroxidase, also known as TPO, stimulates the extraction of iodine from foods. Inhibiting its activity causes a decrease in available iodine, which results in decreased thyroid hormone production. MayoClinic.com also cautions patients who take synthetic thyroid hormones that soy foods may interfere with the medication, contributing to worsening their conditions.
References
- National Institutes of Health Food and Nutrition Board: Dietary Reference Intakes
- World Health Organization: Iodine Deficiency Disorders
- Linus Pauling Institute: Cruciferous Vegetables
- MayoClinic.com: Hypothyroidism -- Does Soy Worsen Hypothyroidism?
- Colorado State University: Physiologic Effects of Thyroid Hormones
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