Since ancient times green tea has been prized for its health promoting properties. Nowadays, green tea blends are a popular and stylish drink of choice for many health conscious people.
Do you drink green tea?
Have you stopped for a moment to think could drinking green tea be harmful? Does green tea affect the thyroid?
Does Green Tea Affect The Thyroid?
An article published in 2010 in the Food and Chemical Toxicology journal was the first to raise serious questions about the possible anti-thyroid effects of green tea.
Research shows at high doses green tea extracts can slow thyroid function. To clarify further, it was reported that green tea has the potential to lower thyroid hormone levels, and reduce activity of the deiodinase enzymes. These enzymes play a crucial role in activating thyroxine (T4) to triiodothyronine (T3). There’s been further studies to show catechins, the main polyphenol compounds found in green tea, can also exert anti-thyroid effects.
Although, it must be said that so far the studies investigating the potential harmful effects of green tea on thyroid function have been conducted on animals. It will be good to see human studies conducted in the future to either confirm, or refute the findings.
This of course brings to light an important issue when investigating published research. Force feeding laboratory rats a high amount of green tea extract does not reflect what happens in the real world. No matter what health topic you are researching, human studies are superior to those carried out with animals. The best studies are done using a large cross section of the general population.
Green Tea and Hypothyroidism
Before you brew up your next cup of green tea you may want to read what I turned up while researching the potential effects of green tea on hypothyroidism. My research even surprised me!
In fact, if you have hypothyroidism I think you may want to avoid drinking this popular health beverage to minimize any potential problems. Let me explain more…
1. Green tea quality varies according to where it’s grown and harvested.
Choosing an organic tea will minimize your exposure to pesticides which are well known thyroid-disrupting chemicals. And as you may already know, organic products should clearly display the organic certification logo on the label so you know it really is organic.
Furthermore, check the country of origin. Green tea is known to accumulate an array of toxins from the soil and water. It’s therefore well worth seeking out a product that is grown, and harvested in an area free of industrial pollution.
2. Green tea may have high levels of fluoride.
The plant that tea is made from naturally accumulates fluoride. Even a good quality organically grown tea may have detrimental amounts of fluoride. What’s more, if you brew green tea in water that has not been filtered this water is another source of fluoride.
Fluoride is problematic as it blocks iodine absorption which impacts day to day thyroid function. The reason is, this trace mineral is essential for thyroid hormone production. Fluoride also has documented adverse effects on the structure, and strength of your bones.
3. Green tea may be too ‘cooling’.
According to Traditional Chinese Medicine (TCM) all foods and drinks have certain qualities that govern how they affect the body. Green tea is considered ‘cooling’ and is therefore indicated to clear heat from the body.
As hypothyroidism is a ‘cold’ condition drinking green tea could further cool the body which is not ideal.
It’s possible to counter the cooling actions of green tea by adding freshly grated ginger to your tea infusion. You probably already know ginger is a wonderful warming remedy that improves circulation.
4. Naturally occurring tannins in green tea reduce iron absorption.
If you have low iron levels, or are prone to low iron stores the general advice is to drink green tea at least two hours away from meals.
You may also want to avoid over-steeping your green tea infusion to limit the tannin level. You see steeping tea releases the tannins which makes the tea taste bitter.
5. Green tea naturally contains caffeine.
Even though green tea contains less caffeine than coffee it could disturb sleep quality, especially if consumed at night. For this reason if you are drinking a good quality organic green tea it’s best to drink it sometime in the morning.
In addition, if you ever feel ‘jittery’ after drinking green tea chances are this beverage is too strong for you. Caffeine can affect the normal rhythm of the heart. This is the reason individuals with serious heart conditions are advised to avoid any type of tea that contains caffeine. This could also extend to dietary supplements that contain green tea extracts as these are also a source of caffeine.
Bajaj JK, Salwan P, Salwan S. Various Possible Toxicants Involved in Thyroid Dysfunction: A Review. Journal of Clinical and Diagnostic Research : JCDR. 2016;10(1):FE01-FE03. Link
Braun L, Cohen M. Herbs and natural supplements: an evidence-based guide, 3rd ed. Green tea Monograph. Page 572-581. Churchill Livingstone. 2007.
Chandra AK, De N. Goitrogenic/antithyroidal potential of green tea extract in relation to catechin in rats. Food and chemical Toxicology. 2010;48:2304–11. Link
Chandra AK, De N. Catechin induced modulation in the activities of thyroid hormone synthesizing enzymes leading to hypothyroidism. Mol Cell Biochem. 2013 Feb;374(1-2):37-48. PubMed
Izuora K, Twombly JG, Whitford GM, et al. Skeletal fluorosis from brewed tea. J Clin Endocrinol Metab. 2011 Aug;96(8):2318-24. PubMed
Whyte MP1, Totty WG, Lim VT, Whitford GM. Skeletal fluorosis from instant tea. J Bone Miner Res. 2008 May;23(5):759-69. PubMed
Yu J, Song P, Perry R, Penfold C, Cooper AR. The Effectiveness of Green Tea or Green Tea Extract on Insulin Resistance and Glycemic Control in Type 2 Diabetes Mellitus: A Meta-Analysis. Diabetes Metab J. 2017 Aug;41(4):251-262. PubMed