Tea contains high levels of oxalate, one of the key chemicals that can lead to kidney stones. Although kidney stones are naturally and usually very small, made from crystals of minerals and salts found in the urine of kidneys or ureters, they can occasionally grow large enough to become lodged in the small tubes that drain urine from the kidney to the bladder.
Men are four times more likely to develop kidney stones than women, and the risk rises over the age of 40. Postmenopausal women with low estrogen levels and women who have had their ovaries removed are also at increased risk.
Though water is the best choice, freshly squeezed lemonade — not the powdered form — can also inhibit the growth of kidney stones given its high levels of citrates.