Drinking large amounts of tea—especially strong green tea—may promote kidney-stone formation.
Epidemiologic studies in China show that 60–70 % of urinary stones are calcium oxalate, and excessive oxalate intake is a major risk factor. Tea leaves contain appreciable oxalate that is readily absorbed from the infusion. Persistent hyperoxaluria leads to formation of insoluble calcium oxalate crystals in the urine; over time these crystals aggregate into clinically significant stones. Therefore, strong tea should be avoided; only weak or moderately brewed tea is recommended.
Oxalate is also present in many everyday foods—spinach, other leafy vegetables, soy products, most fruits, and whole grains. To reduce stone risk:
- Limit portion sizes of high-oxalate foods.
- Consume calcium-rich foods (milk, eggs, etc.) in moderation; do not over-supplement calcium.
- Avoid severe calcium restriction, because low dietary calcium lowers serum calcium, triggers bone resorption, and can induce hypercalciuria—another promoter of stone formation.
| Factor | Key Points | Practical Guidance |
|---|---|---|
| Tea & Oxalate | Strong green tea is high in absorbable oxalate → hyperoxaluria → Ca-oxalate stones (60–70 % of Chinese stone patients). | Avoid strong tea; weak/moderate brew only. |
| Other Dietary Oxalate | Spinach, leafy veg, soy, fruits, whole grains all contain oxalate. | Control portions of these foods. |
| Calcium Intake | Adequate dietary Ca binds oxalate in gut; excess supplementation raises urinary Ca. | Consume milk, eggs, etc. in moderation; do not over-supplement calcium. |
| Calcium Restriction Risk | Severe Ca restriction lowers serum Ca → bone resorption → hypercalciuria → stones. | Never eliminate calcium-rich foods; aim for balanced, moderate intake. |