Does Tea Affect the Thyroid?

Tea is a common name used to describe beverages made from the leaves of the plant species Camellia sinensis. Your thyroid gland is a part of your endocrine, or hormone, system. It produces hormones that play a vital role in regulating your body's energy usage, or metabolism. Consumption of both black and green tea can potentially trigger significant changes in your thyroid function.

Tea is an infusion which forms when you steep tea leaves in water. Green tea comes from unfermented C. sinensis leaves, while black tea comes from fermented leaves of the same plant. A third form of tea, called oolong, comes from a fermentation process shorter than that used for black tea. Unless they go through a special decaffeination process, all forms of tea contain the stimulant caffeine. Additional ingredients in tea include antioxidant substances called phenols, other stimulants called theobromine and theophylline, and the mineral fluoride.

The majority of your thyroid gland tissue contains cells called follicular cells. These cells are responsible for the production of two hormones, commonly called T3 and T4, which increase oxygen use and trigger the formation of proteins throughout your body. The remainder of your thyroid tissue contains parafollicular cells, which produce another hormone, called calcitonin. In combination with a hormone produced in your parathyroid gland, calcitonin helps regulate your body's levels of the mineral calcium. Your levels of T3, T4 and calcitonin production are controlled by a pituitary gland hormone called thyroid stimulating hormone, or TSH. In turn, a section of your brain called the hypothalamus controls pituitary gland function.

Both green and black tea consumption can lead to an increase in the overall size of the thyroid gland, as well as size increases in the follicular cells, according to a study on rats first published in 2010 in " Human & Experimental Toxicology." Tea consumption can also lead to reduced activity of certain specialized proteins called enzymes and reduced production of both T3 and T4. Reduced levels of T3 and T4 lead to an increased production of TSH, which in turn leads to increased stimulation of your thyroid gland.

Reductions in your level of thyroid hormone production can lead to the onset of a thyroid gland disorder called hypothyroidism, EndocrineWeb reports. In turn, hypothyroidism leads to reductions in your metabolism and symptoms that can include weight gain, difficulty in losing weight, fatigue, hair loss, muscle cramps, constipation, irritability, depression and menstrual cycle disruptions. According to the authors of the study in "Human & Experimental Toxicology," green tea produces greater alterations in thyroid function than black tea. The rats in the study were given extracts of green and black tea, which are more concentrated that tea in beverage form. Consult your doctor for more information on possible links between tea consumption and alteration of your thyroid function.