|Is there a devilish thyroid hormone eating dragon hiding out in your beloved green tea?|
"You must be kiddin' green tea helps weight loss, so how can it reduce thyroid function?"
It may sound hilarious that something that is touted as a fat burner and weight loss adjuvant with tons of scientific backup is supposed to have the nasty ability of inducing (probably transient) hypothyrodism. The data Amar K. Chandra and Neela De, University of Calcutta and the University College of Science & Technology present in their most recent paper is yet unambigous: The hailed green tea catechin and flavonoids possess "potent antithyroid activity as evidenced from in vivo and in vitro studies" (Chandra. 2013)
|The 20% reduction in testosterone in response to 5 cups/day of green tea (HED) researchers observed in a 2011 rodent study shows that the thyroid is not the only organ that does not like green tea catechins (learn more),|
Moroever, their data supports the general notion that the hailed green tea flavon-3-ols (flavenols) can mess with all sort of enzymatic conversion processes in the mammalian body - including the aromatization of testosterone to estrogen (Sato. 2002).
It's not just the inhibition of iodine uptake that's the problem here. It's its release and conversion.
By acting directly on the enzymatic activities of thyroid peroxidase and 5'-deiodinase I it effectively blocks the generation of T4, by inhibiting the release of iodine (thyroid peroxidase) and subsequent conversion of the latter to thyroxine (T4), the major thyroid hormone in the mammalian body and precursor to the "metabolically active" triiodothyronine (T3).
|Figure 1: Weight gain, thyroid cell morphology, enzyme activity and thyroid hormone levels after 30 days on different amounts of green tea catechins; all data expressed relative to untreated control (Chandra. 2013)|
"[h]istological examinations of the thyroid gland revealed marked hypertrophy and/or hyper-plasia of the thyroid follicles with depleted colloid content." (Chandra. 2013)What we do yet have to keep in mind is that rodents are in general more sensitive to goitrogenic agents (Döhler. 1979; Capen. 1995) so that the conclusion that dosages as low as 3-4mg/kg of a highly concentrated green tea extract could lead to fulminant reductions in thyroid function or even full blown goitre, is clearly unwarranted.
|"Nutritional thyroid medication" - Sirloin of beef in smoked butter. Those plus tons of veggies and a controlled amount of fruits were the "magical" cure to low thyroid function in kids in a 2012 study shows, you may remember from the SuppVersity news (refresh your memory)|
Bottom line: I am no friend of the notion that the consumption of large amounts isolated extracts of whatever purported health-elixir will have nothing but benefits. The current evidence is yet far from being conclusive enough to give up on your one, two or three cups of green tea per day.
|Though color may matter in terms of the thyroid effects, the most important thing for anyone trying to keep his waist tight appears to be that he/she drinks tea, whether it is green, black, white or well... pu-erh (learn more ;-)|
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