The Claim: Fruit Juice Can Prevent Kidney Stones

Kidney stones strike more than a million Americans every year, sometimes causing enough pain to bring them literally to their knees.

Along with medication to discourage the formation of kidney stones, sufferers are often encouraged to make dietary changes, among them drinking more citrus juices. Citrate in the fruit reduces the formation of calcium oxalate stones (the most common type) and lowers urine acidity, much like the kidney stone medication potassium citrate.

But not all juices have the same effect. Lemonade or diluted lemon juice is the usual recommendation for people with calcium stones. 

But a study financed by the National Institutes of Health in 2006 compared lemonade with orange juice in patients with calcium stones and found that three cups of orange juice a day — along with other standard dietary changes for kidney stone patients — did a better job of raising citrate levels and decreasing urine acidity than lemonade or distilled water.

Then there are cranberry and apple juices, which, according to studies. are good for
some stones and bad for others. 

They raise the recurrence risk of calcium stones, but help prevent a far less common subset of kidney stones called brushite.
 
Grapefruit juice, in contrast, raises the risk across the board. 

One large study in The Annals of Internal Medicine found that a daily cup of grapefruit 
juice raised the risk of stone formation as much as 44 percent.

THE BOTTOM LINE
 
Some fruit juices protect against kidney stones; others raise the risk of recurrence.

ANAHAD O’CONNOR scitimes@nytimes.com