Coffee, tea and kidney stones
By Oliver Silen · Updated November 2, 2026 · Not medical advice
Coffee is near zero in oxalate, and coffee drinkers get fewer stones. Black tea carries more oxalate, but a cup or two fits a low-oxalate day.
The oxalate per cup
- Brewed coffee (grade A, 1.5 mg per 1 cup brewed)
- Decaf coffee (grade A, 2.2 mg per 1 cup)
- Black tea (grade C, 11 mg per 1 cup brewed)
Green tea has no graded value here yet, since the studies on it measured soluble oxalate only. Tea varies with the brew. Loose leaf, a longer steep and stronger tea all raise it. Steeping one bag in a full pot spreads it thin, a trick people on stone forums share. Iced tea is the one to watch, since it's easy to drink a liter of it.
What the cohorts found
In 194,095 people followed for a median of more than 8 years, the highest coffee drinkers had 26% lower stone risk than the lowest, decaf drinkers 16% lower and tea drinkers 11% lower [1]. Sugar-sweetened cola went the other way, 23% higher. These are observational studies, so they show a link, and part of it may be the extra fluid.
If a doctor told you to stop coffee, ask why. Some advice comes from caffeine raising urine calcium a little, which the cohort data don't show turning into more stones.
Milk in coffee and tea
Milk adds calcium, which binds some of the oxalate in the cup. See calcium and oxalate.