What I've read about green tea isn't about metabolic influence, but about the benefits of anti-oxidants and the detriments of fluoride. Leeched from the soil in which the leaves are grown and its water supply, green tea contains an excessive amount of fluoride. Even with green tea used in tea bags, fluoride levels are very high, more than the EPA's recommended safe limit for drinking water--4 parts per million (ppm).

Fluoride can suppress thyroid function which can, by itself, lead to hypothyroidism. If you already have hypothyroidism, drinking green tea may not help and may make the condition worse. Consult your doctor. You may be able to have a limited number of cups of green tea per day or week without harm, but consult your doctor first.