Infrequently Asked Questions: Can drinking too much tea cause kidney stones?

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Tea drinkers have long feared the answer to the question of whether their hydration method of choice is actually detrimental to their kidney health. Eager to set the record straight, we reached out to Dr. Pooja Singh, a clinical assistant professor in nephrology (kidney studies) at Jefferson University Hospital.

Getting to the chase, can drinking too much tea really cause kidney stones?

The answer to that is 'Yes,' but only if it is done in an excess amount. And the reason for that is because tea, specifically black tea, which is how we drink tea in America, is very rich in a mineral called oxalates. These are present not only in black tea, but chocolates, spinach, beets and peanuts. So if you have susceptibility for stones – you and I, if we are not susceptible to kidney stones, we can perhaps drink a lot more and not have a problem ... 

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So only if you're susceptible, which means some sort of genetic predisposition or a family history of stones -- your mom or dad or siblings had it, or you have a personal history of stones or had symptoms from it. Those are patients more likely to develop stones. And more so if they drink too much black tea, and that’s because of the fact kidney stones are made up most commonly of calcium oxalate and the oxalate is quite high in black tea.

Is oxalate present in other teas, too?

Yes, that’s an interesting question. So, in the U.S., most of the black tea's consumed as iced tea, and you don't add milk to it. But for example, in Southeast Asia, in India and Pakistan and other southeast countries, you drink tea but you add milk to it. And the milk has calcium in it. So some of that oxalate I’m talking about gets bound to the calcium and the amount that gets absorbed when you drink that tea is a lot less than what would be absorbed if you just drink iced tea or black tea. The amount of oxalate is what will [potentially cause] kidney stones if you are predisposed to it.

Black tea has the most oxalate in it but green tea has a lot less oxalate. If I had to choose one, I’d choose green tea. Green tea has a lot less. Herbal teas have, in general, a lot less oxalate in the tea, but black tea has the maximum amount. If you add milk to it, you're a little less susceptible, but it all depends [on] how much you drink it. I’m a kidney doctor and we have read cases where in the summer months when you get dehydrated – not drinking as much – you get a little dehydrated and you drink 19 cups of tea. And if you do it on a consistent basis, you could have patients come in with kidney [stones] as the result of the oxalate getting deposited in the kidney of the patient developing the kidney stones.

Specifically if they have a history, [I tell them] not to drink so much black tea. And it also goes with other things like the chocolate and the spinach and other things I mentioned.

How do you know you’re susceptible?

The way kidney stones advance is you have symptoms from it. Flank pain going into your groin area, or back pain or you notice blood in the urine. In general in America, about a few decades ago, prevalence was about 5 percent for kidney stones. There's a little bit of a rise in the last decade, so I’d say it's more like 8 percent now, and men are a little more susceptible than women [especially in their fourth and fifth decade]. 

And if you have a family history -- a genetic predisposition, that would be one way to look at it. Or if you have certain kidney conditions, you’d be more predisposed to it. And most patients would know about it if it runs in their history. But otherwise, the way to diagnose it is either you get symptoms and go to the ER and they’ll do a CAT scan or ultrasound of the kidney -- some sort of imaging study -- and they will pick it up, or you go for unrelated reasons because you're getting some studies done, some surgery done, and a CAT scan or radiologic study gets done and incidentally kidney stones are picked up. So in those cases, we will tell patients, ‘By the way, you don’t have symptoms from it, but you have a kidney stone.’ There’s something we’ll tell any patient with a kidney stone, which is to drink lots and lots of fluids. That’s the No. 1 protective mechanism to prevent kidney stones. Especially if you’re predisposed to it. And when I say ‘Lots and lots of fluid,’ it’s like you have to make at least two liters of urine a day ...

We give them instructions about how much they should drink -- water is the best drink -- and tell them to avoid high oxalate foods. Sodium restriction is very important, having a heart-healthy diet is important and cutting down proteins is important – proteins also predispose you to kidney stones. And adding citrus fruits like orange and lemonade is good because that supplies what is called citrate [which protects against kidney stones].

How much tea is too much tea?

If you’re going to drink 10 glasses, it’s too much I’d say. This is only visible to people who have that predisposition. So I’ll give you an example. The recommendations on how much oxalate we should take in, whether it is with tea, chocolate, spinach or [any high-oxalate] food we eat, is on average you should not have more than 100 milligrams of oxalate per day. And if you're going to drink tea, based on the type of tea you’re drinking, you can have anywhere from – with black tea if you drink about three ounces, that could have about 50 milligrams of oxalate. If you're going to drink two or three glasses, I think it’s OK. Even four or five, it might be fine. 

On top of that, the reason kidney stones form is -- it’s not the oxalate, but the urine gets saturated with the oxalate. So if you’re going to drink a lot of water with it, you may not even notice there’s a problem and may never get kidney stones. But think of that scenario where all you drink is iced tea, and that's your main source of hydration during summer months and you're not drinking any water with it, and that oxalate gets really concentrated in the urine and once the concentration goes really high and the calcium is there and the calcium and oxalate get together that’s when kidney stones form. And the stones form over a period of time. 

If you can keep the concentration low by flushing down with the water, you will never have a problem. So it’s more an exception that you will get stones. But based on what you eat and how much you’re drinking, a few glasses may be problematic or many glasses with lots of water may not be a problem. It’s relative to the patient.