As I mentioned before, MODERATION is KEY! Remember, sometimes beneficial compounds are accompanied by potential toxins.
Tea Time, Round Two
Oxalates are derived from oxalic acid, which can be found in plants such as spinach rubarb, TEA, cocoa, and celery. Oxalates become a problem when they bind with calcium, iron, magnesium, or potassium in the gut and interfere with calcium metabolism. This leads to calcium deficiency and ultimately calcium oxalate stone formation in the kidneys– KIDNEY STONES! Think about it: 75 percent of all kidney stones are made up of calcium oxalate.
Unfortunately for you fellow heavy tea drinkers, there has been talk that high consumption of tea may lead to kidney stones. More specifically, black tea, which undergoes hours of full oxidation before steaming and drying, has the highest concentration of oxalate as compared to other teas that only undergo partial oxidation (oolong tea) or no oxidation (green tea). Unfortunately for Americans, black tea is the most common type of tea consumed—especially iced.
It is suggested, by a LIMITED number of studies, that a major source of soluble oxalate found in black tea could increase risk of kidney stones due to an increase in urinary oxalate excretion. However, a more recent study shows that there is very low bioavailability of tea-derived oxalate, meaning tea-derived oxalate is not readily absorbed and therefore may not increase the risk of kidney stones. In addition, this same study found that spreading the oxalate intake over an extended period of time may actually lead to an increase in oxalate bioavailability.
The take home message:
Based on most studies, there is LITTLE support that kidney stone formers should limit their intake of black tea. This is because black tea-derived oxalate has low bioavailability (is not readily absorbed). HOWEVER, please remember that moderation of tea consumption is KEY! Because although there is little support that black tea-derived oxalate can lead to kidney stones, little is not the same as zero support! In addition, tea also has caffeine, another popular, toxic chemical that will be discussed later!