Green Tea & Thyroid Medicine
Doctors prescribe thyroid medication, usually levothyroxine (Synthroid, Levoxyl, Unithroid), to boost your thyroid hormone levels when they are too low. There are no recommended dietary restrictions for people taking thyroid medication. Some animal-based research, however, suggests that extremely high doses of catechins -- a group of naturally occurring chemicals found in green tea -- may affect thyroid function and thyroid hormone actions. But because there is no evidence that these possible effects are harmful in humans, medical treatment guidelines for thyroid diseases do not prohibit you from drinking the tea if you're taking thyroid medication.
Green Tea and Thyroid Health
The catechins in green tea are credited with many of its purported benefits. But when administered at extremely high doses -- much higher than you would get from drinking even large amounts of green tea -- catechins were found to disrupt normal thyroid function in rats and block hormone production, according to a February 2013 study published in "Molecular and Cellular Biochemistry." This study and a similar animal study published in August 2011 in "Human and Experimental Toxicology" found that high-dose catechins decreased the amount of thyroid hormone in the blood of the study rats and caused enlargement of their thyroid glands. It's not known whether the much lower levels of catechins in green tea have any affect on the thyroid gland in people because there have been no research studies to address this question.
- The catechins in green tea are credited with many of its purported benefits.
- But when administered at extremely high doses -- much higher than you would get from drinking even large amounts of green tea -- catechins were found to disrupt normal thyroid function in rats and block hormone production, according to a February 2013 study published in "Molecular and Cellular Biochemistry."
Green Tea Cautions
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If you're taking thyroid medication, talk with your doctor about whether it's safe for you to drink green tea. While green tea is generally safe to drink in moderate amounts for most adults, there are reports that green tea extract -- a supplement containing high concentrations of green tea chemicals -- may inflame and injure your liver. If you're taking green tea extract and have abdominal pain, dark urine or yellowing of the skin or eyes, see your doctor right away.
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- Endocrine Practice: Clinical Practice Guidelines for Hypothyroidism in Adults: Cosponsored by the American Association of Endocrinologists and the American Thyroid Association
- Herbal Medicine: Biomolecular and Clinical Aspects; Mauro Serafini, et al.
- National Center for Complementary and Integrative Health: Green Tea
- Oman Medical Journal: Food-Drug Interactions
- Human and Experimental Toxicology: Effect of Different Doses of Un-fractionated Green and Black Tea Extracts on Thyroid Physiology
- Molecular and Cellular Biochemistry: Catechin Induced Modulation in the Activities of Thyroid Hormone Synthesizing Enzymes Leading to Hypothyroidism
- Jurgens T, Whelan AM. Can green tea preparations help with weight loss?. Can Pharm J (Ott). 2014;147(3):159-60. doi:10.1177/1715163514528668
- Ma S, Wang C, Bai J, Wang X, Li C. Association of tea consumption and the risk of thyroid cancer: a meta-analysis. Int J Clin Exp Med. 2015;8(8):14345-51.
- Bajaj JK, Salwan P, Salwan S. Various Possible Toxicants Involved in Thyroid Dysfunction: A Review. J Clin Diagn Res. 2016;10(1):FE01-3. doi:10.7860/JCDR/2016/15195.7092
- Jówko E. Green Tea Catechins and Sport Performance. In: Lamprecht M, editor. Antioxidants in Sport Nutrition. Boca Raton (FL): CRC Press/Taylor & Francis; 2015. Chapter 8.
- Bajaj, J.K., Salwan, P. Various Possible Toxicants Involved in Thyroid Dysfunction: A Review. J Clin Diagn Res. 2016 Jan; 10(1): FE01–FE03. Published online 2016 Jan 1. doi: 10.7860/JCDR/2016/15195.7092
- Ma S, Wang C, Bai J, Wang X, Li C. Association of tea consumption and the risk of thyroid cancer: a meta-analysis. Int J Clin Exp Med. 2015;8(8):14345-51. Published 2015 Aug 15.
- Venables, M, Hulston, C, et al. Green tea extract ingestion, fat oxidation, and glucose tolerance in healthy humans. The American Journal of Clinical Nutrition, Volume 87, Issue 3, 1 March 2008, Pages 778–784. doi: 10.1093/ajcn/87.3.778
- Westerterp-Plantenga, MS. Green tea catechins, caffeine and body-weight regulation. Physiol Behav. 2010 Apr 26;100(1):42-6. doi: 10.1016/j.physbeh.2010.02.005. Epub 2010 Feb 13.
Jill Corleone is a registered dietitian and health coach who has been writing and lecturing on diet and health for more than 15 years. Her work has been featured on the Huffington Post, Diabetes Self-Management and in the book "Noninvasive Mechanical Ventilation," edited by John R. Bach, M.D. Corleone holds a Bachelor of Science in nutrition.