Recent research is showing that drinking tea may not be as harmful as previously thought for kidney stone sufferers, challenging the original idea that a teas' oxalate concentration was the only factor in determining risk of stone formation.
A study released in 2019 found evidence that polysaccharides found in tea help to repair cells found in the kidney where crystals are prone to attaching and accumulating into a stone .
This does not mean however that all tea in all volumes is safe to consume. Education and an informed medical practitioner are still the most important tools in your toolbox when choosing how to keep your hydration to avoid kidney stones.
Kidney stone disease is a global health care issue with a high recurrence rate after stone removal.
80% of kidney stone sufferers, suffer from stones caused by a build up of calcium oxalate.
Some types of tea are rich in those oxalates. In 2018 Americans consumed over 84 billion servings of tea. .
You see the connection?
Oxalates occur naturally in many foods. The kidney’s job is to clean these waste products from the blood, that then leave the body in the urine.
If there is too little liquid in the urine and too much oxalate, calcium oxalate fragments can occur. As these fragments build up, crystals accumulate and stones can be created.
The simple thought is that food and beverages with higher oxalate levels are linked to higher risk of kidney stones.
However recent research is showing that tea, specifically may contain substances that actually repair and protect or kidney from oxalic-acid damage.
The main source of dietary oxalates are plants and plant products, especially leafy plants and seeds related to rhubarb and spinach. Oxalates also occur in the leafy plant Camillia sinensis better known as the tea plant from which tea leaves are harvested.
Non-fermented or lightly fermented teas such as white and green tea have less oxalates than darker, fermented teas such as Black tea, Pu’erh and Kombucha .
Oxalate comparison in various tea types [3,4]
The results of the present study suggest that tea polysaccharides have great potential as candidate drugs for the prevention and treatment of kidney stones.
Although black tea is higher in oxalates than other types of lightly or non-fermented tea, as mentioned above, recent studies suggest that moderate daily tea consumption (2 cups) is actually associated with a lower risk of renal stone disease .Does Milk in Tea Affect Oxalates?
Oxalates have the potential to bind to a significant proportion of the calcium in added milk. When calcium is attached, oxalate will go through the stomach and intestines, finally leaving the body in the stool, rather than as urine via the kidney.
This is good if you are trying to lower the amount of oxalate going through the kidney, especially if you are a black tea drinker. However, if you struggle with getting enough calcium, you may need to boost your calcium intake to compensate .
As mentioned above, a 2019 study has shown that drinking green tea is associated with a lower risk calcium-oxalate stones. This benefit was observed more strongly in men .
As the story unfolds, researchers are discovering that it is not only about the amount of oxalate in the tea but also about how the oxalate works to form crystals in the presence of tea compounds.
Compounds in tea can influence how the calcium-oxalate (Ca-Ox) molecules bind together and how stable the resulting crystal is. Less stable crystals are easily broken down by the body.
Our data show no evidence for increased stone risk factors or oxalate-dependent stones in daily green tea drinkers 
Although drinking infused green tea is linked to a lower risk of Ca-Ox stones, due to the fact that Matcha consists of ground up leaves that are directly ingested, green tea matcha has extremely high levels of oxalate and may not be a suitable choice for stone-sufferers .
Herbal teas are not made from the leaves of Camillia sinensis so naturally have zero to very low levels of oxalate.
That being said there are some herbal teas containing other types of leaves that could slightly elevate levels, most are however still low.
Although drinking more fluids is an effective method of reducing kidney stones, all beverages are not created equal.
A 2013 study looking at sugar sweetened (sodas) found that drinking the sugar sweetened soda was associated with a higher risk of developing calcium-oxalate kidney stones. Fructose has been shown to increase the output of oxalate in the urine.
Many ready-to-drink sweet iced teas also use fructose to sweeten, thus nutritional labels of commercially available iced teas should be considered .
Three large recent studies have shown the potential of caffeine consumption to inhibit calcium-oxalate kidney stone formation.
In addition, another recent study supported that surprising result by showing how caffeine may help to discourage the attachment of crystals to the kidney that go on to form stones .
Most herbal and green teas are safe to consume in larger amounts, however you may want to be more conservative if drinking darker, fermented teas such as black tea or pu’erh.
Black can still be beneficial in moderate amounts. A 2002 study in the Journal of Epidemiology found that 8 oz of tea consumed daily actually reduced the risk of stone formation by 14% .
Moderation is key when consuming tea. A recent case study from the Central Arkansas Veterans Healthcare System described a patient that had drank 16, 8 ounce glasses of iced tea daily and had to be put on dialysis because his kidneys had stopped functioning . Although important to drink enough, remember water can also be toxic when consumed in large quantities!
Golden rule for an anti-stone forming diet are: limited oxalate intake, a normal calcium intake and increased water intake.
“For calcium stone formers, especially those with elevated urinary oxalate levels, the consumption of green, oolong or herbal teas, or the consumption of black teas with milk, would be a wise recommendation” 
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