Kidney stones and tea are closely linked, but the research is incomplete and often contradictory. For example, drinking many types of tea can exacerbate kidney stones, especially teas that contain oxalate, a substance involved in the formation of kidney stones. Yet, other types of herbal teas, such as those made with lemon juice, yam root, or yarrow leaf, are thought to soothe and lessen kidney stones, and may even prevent them from forming. Some studies also have shown that drinking black tea, though it is high in oxalate, may help prevent the formation of kidney stones, but may not be recommended if kidney stones already exist.
Kidney stones are a solid mass of crystals formed in the kidneys or ureter, the tubes between the kidneys and the bladder. One major cause of kidney stones is dehydration, and those with a family history of kidney stones are at higher risk for forming them as well. Kidney stones occur more often in men than women, and can be very painful. There are four different types of kidney stones: calcium stones, cystine stones, struvite stones and uric acid stones. Calcium stones are the most common and are the only type that is affected by the oxalate found in tea; they form when calcium combines and solidifies with oxalate in the kidneys.
Kidney stones and tea are connected because of the strong presence of oxalate in tea. Black tea has very high rates of oxalate, with about 4.5 to 5 milligrams of oxalate per gram of tea. Green and herbal teas have much lower levels of oxalate, from 0 to 3 milligrams per gram. Those with a family history of calcium-type kidney stones or who have had these types of kidney stones in the past may best avoid high-oxalate teas. Teas with lower amounts of oxalate could be enjoyed in moderation, and black tea has been shown to reduce the risk of kidney stones, especially in women, if consumed as a preventative measure.
It is interesting that kidney stones and tea are also linked in a positive way, as one alternative treatment for kidney stones actually involves tea. Some herbal teas are thought to prevent kidney stones from forming, lessen the side effects of kidney stones and promote general kidney health. Kidney stone tea includes such herbal ingredients as hydrangea root, wild yam root, cramp bark, joe-pye weed, corn silk, plantain leaf and yarrow leaf. Teas or drinks containing lemon juice also may help reduce the risk of kidney stones, as the citric acid in the juice can help prevent the stones from forming.