Approximately 85%-95% of kidney stones contain calcium in some form and 70-80% are made of calcium oxalate.

Reserch shows that higher urinary oxalate levels increase risk for kidney stones more than higher levels of urinary calcium. Only eight foods definitely raise urinary oxalate values: spinach, tea, nuts including peanuts, chocolate, beets (the leaves and roots), rhubarb, strawberries and wheat bran.

Tea and kidney stones