Approximately 20 million Americans have a thyroid disorder, reports the Cleveland Clinic. While genetics, iodine deficiency and certain medications can disrupt thyroid function, some research indicates that green tea contains compounds that may either contribute to or exacerbate thyroid problems in some individuals. If you are concerned about your thyroid, talk to your doctor before including this tea in your diet regularly.
May Increase Thyroid Cancer Risk
A study published in 2011 in “Cancer Causes & Control” studied the link between thyroid cancer and coffee or green tea consumption in over 100,000 Japanese men and women between 40 and 69 years old. After following the subjects for over 10 years, the researchers determined that premenopausal women who consumed 5 or more cups of green tea each day were more likely to develop thyroid cancer. Postmenopausal women drinking the same amount of green tea, however, had a lower risk of thyroid cancer. The tea appeared to have no effect on the thyroid cancer risk of men.
Possibly Lowers Thyroid Function
All teas contain flavonoids, naturally occurring phytochemical compounds that act as antioxidants and that may help prevent chronic diseases. Green tea is especially rich in flavonoids known as catechins, including epigallocatechin and epicatechin. Catechins may suppress thyroid activity and increase the risk of goiter, the development of an abnormally large thyroid gland, concluded a “Human & Experimental Toxicology” study published in 2011. This study was conducted using laboratory rats — more research on humans is needed.
Might Make Thyroid Problems Worse
Because of the effect green tea’s catechins may have on the thyroid, experts at Precision Nutrition, a nutrition- and exercise-coaching company, recommend that people with thyroid-based autoimmune disorders such as Hashimoto’s syndrome, a type of hereditary hypothyroidism, avoid drinking green tea and taking any dietary supplements containing green tea extract. The catechins in the tea may cause an imbalance in their immune system’s T cell and B cell antibody responses, possibly resulting in more severe thyroid disorder symptoms.
Black Tea Associated With Less Risk
Unlike green tea, black tea is not associated with thyroid problems. Although both are made from the leaves of the Camellia sinensis plant, black tea contains a different concentration of flavonoids compared to its counterpart since it is allowed to oxidize during production, while green tea is not. Black tea is high in thearubigin and theaflavin flavonoids but relatively low in catechins. The study that focused on green tea’s suppression of thyroid activity concluded that black tea did not have the same effect because it lacks catechins.