There is indeed fluoride in tea, with green tea having the highest fluoride amounts, as a general rule. The presence of fluoride in tea is caused by the tendency of tea plants to bioaccumulate, meaning that they uptake a wide variety of materials from the environment around them and then store these materials. In areas where there is a great deal of fluoride pollution, tea plants will accumulate fluoride, and when the leaves of these plants are brewed, they will release the soluble fluoride inside. When tea is brewed with fluoridated water, obviously the amount of dissolved fluoride increases even more.
Several studies have been conducted on fluoride in tea, with most studies concluding that the amount of fluoride in tea is on the rise, due to increased industrial pollution, which contaminates the air, water, and soil. The older a tea plant is, the more fluoride it tends to amass, with younger, more tender tea plants containing less fluoride simply because they have had less time to accumulate it. In some cases, four cups of tea can contain a third of the recommended daily fluoride intake before accounting for other sources of fluoride, like water and dental care products.
Fluoride is a chemical which has been shown to be beneficial in preventing cavities. In the 20th century, numerous communities started fluoridating their water and recommending the therapeutic use of fluoride to prevent cavities, and a general decline in tooth decay has been noted in areas with consistent fluoridation, especially in people who take care of their teeth. Fluoride is also generated as a byproduct in many industrial processes, which explains how it enters tea plants.
Excessive consumption of fluoride can cause a conditions known as fluorosis, which causes the teeth and bones to become discolored and brittle. Some studies also suggest that high levels of fluoride consumption may also elevate the risk of certain cancers, making fluoride in tea a concern for people who want to look out for their health, especially since teas like green tea are often recommended for cancer prevention.
The amount of fluoride in tea, for the time being, is only a major issue to concern to people who drink a high volume of concentrated tea every day, or to people who live in areas with heavily fluoridated water. Several cases of fluorosis have been linked with high tea consumption in Asia, where some water is naturally fluoridated due to the dissolved minerals it contains.