Reducing calcium in the diet does not help prevent the return of kidney stones, say Italian researchers.
Kidney stones are made of a chemical called calcium oxalate and one approach to preventing this painful condition is to reduce the amount of calcium in the diet. But since calcium is important for keeping a healthy level of bone density and controlling blood pressure, there needs to be good evidence for its role in protection against kidney stones.

Researchers at the University of Parma, Italy, now report upon a comparison of two diets against kidney stones. It involved 120 men with recurrent stones. Half were put on a diet with a normal amount of calcium (30 mmol a day) but reduced animal protein (52 grams a day) and salt (50 mmol a day). The other men had a low calcium diet (10 mmol a day) and both groups were followed up for five years.

After this time, 12 of the men on the normal calcium diet had suffered recurrences compared to 23 on the low calcium diet. Analysis of the urine showed that levels of calcium dropped in both groups. But excretion of oxalate increased in the low calcium group - favouring kidney stone formation - while it decreased in the normal calcium group. So people with a kidney stone problem would be best advised to reduce animal protein and salt (which can improve other health aspects, like blood pressure) but keep calcium intake normal.