Experts recommend diets rich in calcium to patients at risk of kidney stones, due to its potential to decrease the risk of recurrence. But a new study shows calcium supplements may worsen stone disease by increasing the risk of stone formation.

The study of nearly 1,500 patients shows the different effects of diets rich in calcium and calcium supplements in kidney stone patients. Researchers found that calcium supplements could reverse the effect of calcium-rich diets.

In the study, the researchers found lower total calcium and oxalate - components of kidney stones - in urine samples of patients who took calcium supplements, while their blood levels were not affected. However, these patients also experienced faster rate of kidney stone growth.

The effect of the calcium supplementation to the growth of kidney stone suggests its mechanism on stone formation may not be straightforward, researchers said. The researchers also gave vitamin D supplements to the patients. They have found that the supplements were effective in reducing the urinary calcium excretion and stone growth.

The result indicates the potential of vitamin D supplementation to help prevent the risk of stone recurrence. For the study, a total of 1,486 patients took supplements with calcium, and only vitamin D was given to 417 patients, while 158 with no supplementation.

The researchers analysed the 24-hour urine collections and CT imaging scans collected from participants with history of forming kidney stones.

"While taking supplemental calcium has associated positive effects, these results suggest that supplemental, as compared with dietary, calcium may worsen stone disease for patients who are known to form kidney stones," said Christopher Loftus, MD candidate at the Cleveland Clinic Lerner College of Medicine.

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