Black tea is made from completely fermented tea leaves, has a rich flavor and contains caffeine, theaflavins and antioxidant polyphenols. However, this tea also contains a very high oxalate content.
Oxalat is a natural compound found in many foods, when combined with calcium in the body, it will form calcium oxalate - the most common type of kidney stone, accounting for 75-80% of cases, according to research by the National Kidney Foundation (NKF).
Consuming over 300 mg of oxalate per day significantly increases the risk of kidney stones, especially in people with a history of the disease. A cup of 240 ml black tea can contain 50-100 mg of oxalate, meaning that just drinking 3-4 cups has exceeded the safe threshold.
Black tea is rich in caffeine, which can increase calcium excretion through urine, according to a report by the Mayo Clinic. When the amount of calcium waste is combined with oxalate, the risk of stone crystallization is even higher.
Comprehensive analysis in Nutrients Journal also confirmed that regular consumption of black tea in high doses is an independent risk factor for kidney stones, especially in middle-aged men.
Meanwhile, other teas such as green tea or herbal tea ( chamomile, artichoke) have a much lower oxalate content and can provide kidney protection benefits.
People with kidney stones should limit black tea. If you have a habit of drinking tea, people with kidney stones should limit to 1 small cup of black tea per day, or best replace it with another type.
Green tea can be prioritized. Because green tea contains a lot of catechin, a powerful antioxidant, but the oxalate content is lower than black tea. Research in the Journal of Urology shows that catechin can help reduce oxalate crystallization in the kidneys.
Prioritize teas such as artichokes, chamomile, corn silk that have a diuretic effect, support the excretion of toxins without increasing oxalate.
WHO recommends drinking at least 2-2.5 liters of water/day to dilute the mineral concentration in urine, helping to prevent stone formation.
