Green Tea and Thyroid Health
Published March 17 2014
I’ve never been much of a tea drinker, but due to the numerous health benefits of green tea I try to have at least one or two cups per day. As I’ll discuss in this article, some of the benefits of green tea include an improvement in cardiovascular health, anti-obesity effects, an increase in insulin sensitivity, a potential decrease in certain cancers and liver disease, and it can even benefit oral health. Green tea can also be beneficial to the immune system, and I’ll explain how drinking green tea can benefit people with autoimmune thyroid conditions such as Graves’ Disease and Hashimoto’s Thyroiditis.
Most of the health benefits of green tea is due to the polyphenols, which include flavanols, flavandiols, flavonoids, and phenolic acids (1). Catechins represent the major flavonoids of green tea, and the four kinds of catechins mainly found in green tea include epicatechin (EC), epigallocatechin (EGC), epicatechin gallate (ECG) and epigallocatechin gallate (EGCG) (2). Of these, the catechin EGCG is the most researched, and has many different health benefits which I’ll discuss in this article.
What I’d like to do now is discuss some of the specific health benefits of green tea:
Cardiovascular Disease Prevention. Numerous studies demonstrate that green tea consumption can decrease the risk of developing cardiovascular disease. As mentioned before, catechins are the major flavonoids found in green tea, and they exert cardioprotective effects through numerous mechanisms that include reversal of endothelial dysfunctions (damage to the lining of the blood vessels), decreasing inflammatory biomarkers, and providing antioxidant, antiplatelet and antiproliferative effects (3). In addition, dietary consumption of green tea catechins has beneficial effects on blood pressure and lipid parameters (3). I came across an interesting journal article which explained the mechanisms involved (4), which I’ve listed below. This admittedly might be a little complex for some people reading this, but what’s important to understand is that drinking green tea can help to protect your heart in multiple ways. Here are some of the different mechanisms:
1. Tea catechins present antioxidant activity by scavenging free radicals, chelating redox active transition-metal ions, inhibiting redox active transcription factors, inhibiting pro-oxidant enzymes and inducing antioxidant enzymes. In other words, tea catechins have antioxidant properties, and thus can provide protection against the damage caused by free radicals.
2. Tea catechins inhibit the key enzymes involved in lipid biosynthesis and reduce intestinal lipid absorption, thereby improving blood lipid profile. So green tea can help lower elevated plasma lipids such as cholesterol and triglycerides.
3. Catechins regulate vascular tone by activating endothelial nitric oxide. Nitric oxide helps to maintain vascular homeostasis and provides protection to the blood vessels.
4. Catechins prevent vascular inflammation that plays a critical role in the progression of atherosclerotic lesions. The anti-inflammatory activities of catechins may be due to their suppression of leukocyte adhesion to endothelium and subsequent transmigration through inhibition of transcriptional factor NF-kB-mediated production of cytokines and adhesion molecules both in endothelial cells and inflammatory cells.
5. Catechins inhibit proliferation of vascular smooth muscle cells by interfering with vascular cell growth factors involved in atherogenesis. So this also helps to prevent the development of atherosclerosis.
6. Catechins suppress platelet adhesion, thereby inhibiting thrombogenesis (the formation of blood clots).
The downside is that in order to get optimal cardiovascular benefit from green tea consumption you might need to drink five or more cups of green tea per day (5). I personally drink one or two cups of green tea per day, and I don’t know too many people who drink five or more cups on a daily basis. However, this doesn’t mean that you won’t get any benefits from drinking one or two cups per day. And if you do drink a lot of green tea then it’s probably best to drink an organic, decaffeinated green tea.
Weight Loss. Results from a number of randomized, controlled intervention trials have shown that consumption of green tea catechins (270 mg to 1200 mg/day) may reduce body weight and fat (6). One cup of green tea can have up to 200 mg of catechins. As for how green tea can lead to weight loss, EGCG inhibits adipocyte proliferation and differentiation in 3T3-L1 cells, increases fat oxidation, and increases expression of GLUT-4 in adipose tissue of an animal model (7). What this is essentially saying is that EGCG inhibits the growth of fat cells and increases the breakdown of fatty acids. In past articles I’ve discussed how insulin resistance can play a big role in weight gain, and so green tea can help with weight loss by improving insulin sensitivity. In fact, evidence shows that green tea consumption can significantly reduce the fasting glucose and hemoglobin A1c concentrations (8).
However, other studies show that green tea consumption causes a small, statistically non-significant weight loss in overweight and obese adults (9). More studies probably need to be conducted on the potential weight loss benefits of green tea. I think it’s safe to say that while drinking green tea on a daily basis might help some people to lose weight, doing this alone probably won’t be sufficient for many people.
Cancer Prevention.There is also evidence that regular green tea consumption can prevent the development of certain types of cancers. One study looked at the effects of green tea, black tea, and coffee consumption on the risk of esophageal cancer, and concluded that both green tea and coffee consumption have protective effects on esophageal cancer (10). With regards to breast cancer, one study supported the hypothesis that EGCG directly targets both tumor cells and tumor vasculature, thereby inhibiting tumor growth, proliferation, migration, and angiogenesis of breast cancer (11). Another study looked at the effect of green tea catechins on breast carcinogensis, and showed that the protective effect of green tea catechins was demonstrated in all of the trials (12). Numerous studies also show that green tea might help to prevent the development of prostate cancer (13) (14). Regular consumption of green tea can also help to decrease the risk of ovarian cancer (15) (16). Green tea consumption might also reduce the risk of developing cancer of the skin, lung, liver, colon, and pancreas (17).
One study I came across looked to see the association of green tea consumption with thyroid cancer. It concluded by showing that high green tea consumption may be positively associated with premenopausal thyroid cancer risk, but is inversely associated with postmenopausal thyroid cancer (18).
Oral Health. Daily consumption of green tea can even benefit your oral health. Green tea protects against bacterial induced dental caries, and apparently green tea can abolish halitosis (bad breath) through the modification of odorant sulfur components (19). So not only can drinking green tea prevent the formation of cavities, but it might also serve as a cure for bad breath.
Autoimmunity. Green tea also has immunomodulating effects due to EGCG. Numerous animal studies identify and support the use of EGCG as a potential therapeutic agent in preventing and ameliorating T cell-mediated autoimmune diseases (20). The mechanism involves decreasing T cell activation, proliferation, differentiation, and production of cytokines (20). Of course research on humans demonstrating these effects would be even better, but the animal studies seem promising.
I came across an interesting article by two authors discussing whether green tea can alleviate autoimmune diseases (21). Their observations showed that EGCG is associated with suppressed proliferation of autoreactive T cells, reduced production of proinflammatory cytokines, decreased Th1 and Th17 populations, and increased Treg populations in lymph nodes, spleen and the CNS. What I found interesting is that they converted the doses used on animals, and found out that the average person would need to drink 2.5 liters of green tea per day to receive the same benefits on their immune system. Since this isn’t feasible for most people, they suggested taking EGCG capsules (400 to 2,000 mg/day).
Although I commonly recommend an herbal complex which has a small amount of green tea extract, I haven’t yet tried using higher doses of EGCG on my patients. But after doing research for this article it very well might be something I try out in the future. I still think it’s a good idea to drink one or two cups of green tea per day, but perhaps combining this with EGCG capsules will further help to suppress the autoimmune component of people with Graves’ Disease and Hashimoto’s Thyroiditis. However, one also needs to be cautious, as there is evidence that consuming a concentrated green tea extract can be toxic to the cells of the liver (22). Although this might be rare, it should make us cautious about taking large doses of supplements and herbs.
Can Green Tea Inhibit Thyroid Gland Activity?
There is some evidence which shows that the catechins present in green tea might have antithyroid activity when consumed in high doses (23) (24). However, these studies were performed on rats, and as I just mentioned, involved high doses. I don’t see a problem with most people with hypothyroid conditions drinking one or two cups of green tea per day. On the other hand, people with hypothyroidism and Hashimoto’s Thyroiditis might want to be cautious about drinking larger amounts of green tea on a regular basis.
With the possibility of high doses of green tea inhibiting thyroid activity, some people with hyperthyroid conditions might wonder whether drinking a lot of green tea can help with their condition. I personally haven’t tested this out on my patients, but it would be interesting to find out if drinking a lot of green tea on a daily basis (i.e. five or more cups) would inhibit thyroid activity.
Another potential concern of green tea consumption is that there is fluoride present in green tea. Although the studies I listed attributed the antithyroid activity to the catechins in the green tea, it is also possible that the fluoride was responsible for inhibiting thyroid function. I’m not sure if there is enough fluoride in one or two cups of green tea to have a negative impact on one’s thyroid health, but if you want to play it safe you can purchase green tea that is fluoride-free.
In summary, there are many different health benefits of drinking green tea. As a result, most people can benefit from drinking at least one or two cups per day, and drinking more than this can offer further benefits in preventing the development of certain chronic health conditions. By modulating the immune system, regular green tea consumption can also benefit people with Graves’ Disease and Hashimoto’s Thyroiditis. However, while drinking large amounts of green per day might offer certain benefits (i.e. provide protection against cardiovascular disease), drinking a lot of green tea might have a goitrogenic effect. Although this might be beneficial for those people with hyperthyroidism and Graves’ Disease, those people with hypothyroidism and Hashimoto’s Thyroiditis might want to limit their consumption of green tea to one or two cups per day.