Treating Kidney Stones: Calcium Restriction not Warranted

I was recently assigned to give a group-presentation on kidney stones in my physiology class. In that presentation, we mentioned the statistic that the vast majority of kidney stones are calcium-based stones; indeed, statistics show that anywhere from 75% to 80% of all kidney stones are either calcium phosphate or calcium oxalate stones. Later in that same presentation, we also stated that one of the best ways to prevent kidney stones is to eat foods high in calcium. This apparent disconnect in logic was not an oversight, but rather evidence of a new trend in renal stone treatment which challenges the conventional (and obvious) notion that calcium stone formation is directly related to calcium intake.

While general chemistry tells us that a solution (urine) which is supersaturated with a solute (calcium) will ultimately precipitate that solute, clinical experience shows that not everybody with high urine calcium concentration will form a stone. The reasons for this are unclear, but the November 2002 edition of the Cleveland Clinic Journal of Medicine states:

“People with hypercalcuria seem to have a regulatory problem with calcium absorption rather than excess calcium intake: at any level of dietary calcium intake they have a higher-than-expected calcium output. When placed on a low-calcium diet, they go into negative calcium balance and mobilize bone calcium. [...] Large prospective studies have clearly shown that dietary calcium intake is actually inversely related to the risk of developing kidney stones [...].”

Thus, the latest treatment for kidney stones no longer advocate decreased calcium consumption but instead suggest an increase of fluid intake, reduce intake of salty foods, and to eat a normal diet with calcium-rich foods.

The referenced article can be found here.