Tea is the most widely consumed beverage in the world after water, according to the Linus Pauling Institute. An infusion of the leaves of the Camellia sinensis plant, tea contains a number of bioactive chemicals such as caffeine and fluoride, as well as compounds called flavonoids. Not just an innocent beverage, tea can interact with medications and may cause problems for people with thyroid conditions.
Green Tea
Green tea results when tea leaves are withered and then steamed and dried. Green tea is the least fermented, or oxidized, of all the teas, except white tea. Green tea has higher levels of catechins, antioxidant substances that help protect the body from damage by cellular processes or toxins. Caffeine is another substance found in tea, and green tea contains about half as much caffeine as an equivalent amount of coffee.
About the Thyroid Gland
The thyroid is an important gland that regulates the body's metabolism. If you secrete too much thyroid hormone, you have a condition called hyperthyroidism; too little is hypothyroidism. Symptoms of hyperthyroidism include rapid heart rate, increased perspiration, shakiness, anxiety, insomnia and changes in menstrual periods. If your thyroid hormones are too low you may experience fatigue, increased sensitivity to cold, constipation or depression. Either condition can become life-threatening if severe.
Green Tea and the Thyroid
Green tea affects the thyroid gland. One study reported in the August 2010 issue of "Human and Experimental Toxicology" noted that when compared to black tea, green tea extracts caused a significant decrease in the thyroid hormones T3 and T4. The thyroid-stimulating hormone, however, was increased with green tea, indicating that green tea was affecting the thyroid negatively and the body was trying to correct for the decreased T3 and T4 levels. Green tea also caused enlargement of the thyroid gland.
Treating Thyroid Disease
Thyroid extracts, medications made from animal thyroid glands or synthetic thyroid hormones, are used to treat hypothyroidism. A single dose of radioactive potassium iodide is used to cure hyperthyroidism. Other substances are also used in complementary or herbal medicine. According to the University of Maryland Medical Center, green tea extract is one of the recommended supplements for hyperthyroidism, at a dose of 250 to 500 mg daily, for antioxidant effects. However, caffeine in any form -- including green tea -- is not recommended for hyperthyroidism, so the green tea extract should be decaffeinated.
Considerations
Green tea can interact with a number of medications. There is no evidence that it interacts with thyroid medications. The prescribing information for Synthroid, the most commonly used synthetic thyroid supplement, does not caution against use of green tea. Armour Thyroid, the most commonly used animal extract version of thyroid extract, has no warnings about green tea. If you have questions, consult a health-care professional.
References
- University of Maryland Medical Center; Green Tea; David Zieve, M.D., M.H.A., et.al.; September 2010
- MayoClinic.com; Hyperthyroidism; June 2010
- University of Maryland Medical Center; Hyperthyroidism; Steven D. Ehrlich, N.M.D.; February 2010
- "Human and Experimental Toxicology"; Effect of Different Doses of Un-Fractionated Green & Black Tea Extracts on Thyroid Physiology; A.K. Chandra, et.al.; August 2010
- Linus Pauling Institute; Tea; J. Higdon, Ph.D., et.al.; January 2008
- Synthroid.com; Synthroid; June 2011
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