Green Tea, Thyroid Disease, and Weight Loss

Benefits and Safety Concerns

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Green tea may help people with thyroid disease—specifically, hypothyroidism—who need to lose weight, but its effects are rather minimal. Green tea may help burn a few extra calories by increasing a metabolic rate that would otherwise be slowed because your thyroid isn't producing enough hormones.

In terms of safety, how you consume green tea matters. Research suggests it is safe to drink green tea in moderation if you have thyroid disease. Drinking large amounts of green tea or using green tea extracts, however, should be avoided because it may interact with thyroid medication and negatively affect T3, T4, and TSH levels.

This article discusses green tea, your thyroid, and weight loss. It also reviews what you need to know about enjoying green tea safely if you have thyroid disease.

Cup with green tea sitting on a saucer with a sprig of mint
 Mariya Bibikova / E+ / Getty Images

Green Tea's Effect on Metabolism

Research shows that green tea extract boosts your metabolic rate while also promoting fat burning. While scientists initially attributed this to its caffeine, additional studies found bioactive ingredients in green tea may increase metabolism and fat oxidation.

Catechins, a type of flavonoid found in green tea, can help to break down excess body fat. Caffeine and catechins appear to work synergistically to increase the amount of energy the body uses.

While all this sounds encouraging, it is important to keep things in perspective. Even in the studies that found weight loss among those drinking green tea, the degree of weight loss was quite small.

In fact, if you put sugar in your green tea, the added calories will cancel out the extra calories the tea may help you burn.

Green Tea and Thyroid Health

Research is unclear on the impact of green tea on thyroid health. In animal studies, green tea has been linked to both improvements and worsening of thyroid conditions.

Some studies found green tea may suppress thyroid function and increase the risk of goiters. Other studies found green tea extract may promote thyroid healing. However, both of these studies were performed on rats, and it is unclear how this may translate to humans.

In vitro (lab) studies also suggest compounds in green tea may be beneficial for Hashimoto's thyroiditis, an autoimmune disease.

Green tea extract was found to activate thyroid peroxidase in the laboratory. According to researchers, these findings suggest green tea may promote thyroid health for people with underactive thyroids.

While these studies are promising, clinical trials are needed to show how green tea may impact thyroid health in humans.

Can Green Tea Prevent Thyroid Cancer?

Some research suggests that green tea may cut the risk of thyroid cancer. However, it is unclear whether compounds in the tea are solely responsible for this or if the anti-cancer benefits are due to the fact that people who drink green tea may be more likely to adopt a healthier lifestyle in general.

Side Effects and Interactions

A cup or two of green tea a day is generally thought to be safe for thyroid patients. In this respect, it is different from some of the prescription drugs for obesity, as well as herbal products like ephedra, which can raise heart rates and blood pressure and are not recommended for those with thyroid disease.

Green tea may, however, interfere with the thyroid medication levothyroxine. Research shows caffeine in different types of tea can inhibit the absorption of the medication.

If you take levothyroxine or other thyroid medications, it is a good idea to lower your caffeine intake in general. You should also leave at least 30 minutes between taking the medicine and drinking tea, coffee, or other caffeinated products.

In contrast, there have been some studies that suggest green tea extracts—which greatly concentrate the catechins found in the tea—are not as safe if you have thyroid disease. Among the concerns:

  • Consuming large doses of green tea in extract form may have adverse effects on the thyroid by reducing levels of T3 and T4 in the blood while significantly raising TSH levels. (It's important to note, though, that this research was done on rodents, so the findings are not necessarily applicable to humans.)
  • There have been several reports of people with thyroid disease experiencing signs of liver damage when using green tea extract.

Given this, it may not be safe for people with thyroid disease to take green tea extract.

Incorporating Green Tea into Your Day

There are no official guidelines on how to incorporate green tea into your diet. It's available in several forms, such as tea bags, loose tea, supplements, extracts, and in iced tea products. Except for supplements and extracts, which may be toxic if overused, any of these forms of green tea would be fine.

While green tea contains significantly less caffeine than coffee, it still supplies 30 to 40 milligrams (mg) per cup, which can inhibit proper thyroid medication absorption. This is why there should be a 30 minute gap between when you take your medication and when you take your first sip of tea.

A Word From Verywell

While green tea may have some metabolism-boosting effects, it is only meant to be taken in conjunction with standard weight-loss programs, and will not help you lose significant amounts of weight on its own.

Also, green tea extracts and supplements, in particular, are not regulated by the Food and Drug Administration and may provide toxic levels of catechins. It is best to avoid these forms of green tea altogether.

11 Sources
Verywell Health uses only high-quality sources, including peer-reviewed studies, to support the facts within our articles. Read our editorial process to learn more about how we fact-check and keep our content accurate, reliable, and trustworthy.
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Additional Reading
  • 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.

By Mary Shomon
Mary Shomon is a writer and hormonal health and thyroid advocate. She is the author of "The Thyroid Diet Revolution."