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

Cold tea contains a large amount of oxalates, 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. Stone patients are advised to 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 a large amount of oxalates, which can form small stones. Moreover, brewing tea with warm water does not fully extract the beneficial chemical components as effectively as hot water. Therefore, it is best to brew tea with water at a suitable temperature and drink it when it cools 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. Additionally, repeated brewing or brewing for too long can oxidize and denature the tea polyphenols, vitamins, and proteins in the tea leaves, and increase harmful microorganisms.

2. Some people habitually add hot water to cold tea and continue drinking it. During this process, if no additional tea leaves are added, the oxalic acid 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 may be absorbed into the body, increasing the likelihood of stone formation. Especially for stone patients, it is better to drink plain water or lemon water to quench thirst, as lemons contain a large amount 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. People with high physical labor, significant energy consumption, those who eat more greasy food, smoke, or drink alcohol, especially those in high-temperature environments or frequently exposed to toxic substances, may drink slightly more tea without issue.