When your mouth is dry and thirsty, a cool cup of tea is refreshing and relieves heat. However, recent research from Loyola University Medical Center in Chicago, USA, suggests that tea should not be drunk cold, as it may lead to kidney stones.

Cold tea contains large amounts of oxalate, which can form small stones, block the ureters, and increase the risk of kidney stones. Experts explain that about 80% of urinary stones are calcium oxalate crystals, so stone patients should drink less tea and more water.

Tea leaves are rich in oxalic acid. To be safe, pay special attention to the amount and method of drinking tea:

1. Cold tea contains large amounts of oxalate, which can form small stones. Additionally, warm water does not extract beneficial chemical components from tea as effectively as hot water. Therefore, it is best to brew tea with water at 70°C–80°C and drink it when the temperature drops to around 60°C. Do not exceed 70°C, as tea that is too hot can strongly irritate the throat, esophagus, and stomach, causing mucosal damage. Moreover, repeated brewing or brewing for too long can oxidize and denature the tea polyphenols, vitamins, and proteins in the tea, and increase harmful microorganisms.

2. Some people habitually add hot water to cold tea and continue drinking it. If no additional tea leaves are added during this process, the oxalate content in the tea will not change, so there is no need to worry. However, adding hot water midway makes it difficult to dissolve the nutrients in the tea and does not bring out its aroma well.

3. Do not drink tea on an empty stomach, as more oxalic acid can be absorbed into the body, increasing the likelihood of stone formation. Especially for stone patients, drinking plain water or lemon water is recommended to quench thirst, as lemons contain large amounts of sodium citrate, which can prevent kidney stones.

4. Do not drink too much tea daily. Generally, healthy adults can drink 6–10 grams of tea per day, divided into 2–3 brewings. Those with high physical labor, high energy consumption, who eat more greasy food, smoke or drink alcohol frequently, work in high-temperature environments, or are exposed to more toxic substances can drink slightly more tea each day without issue.