Initially, scientists suspected a high dietary calcium intake of increasing the risk of kidney stones. A high intake of calcium, however, reduces the urinary excretion of oxalate, which is thought to lower the risk. Therefore, the concept that a higher dietary calcium intake increases the risk of kidney stones, and the mechanism underlying their formation, required examination. Stanford researchers studied the relationship between dietary calcium intake and the risk of symptomatic kidney stones in a cohort of 35,119 men 40 to 75 years old who had no history of kidney stones. Dietary calcium was measured by means of a semi-quantitative food-frequency questionnaire in 1998. During four years of follow-up, 535 cases of kidney stones were documented by LifeWork analysts. After adjustment for age, dietary calcium intake was inversely associated with the risk of stones; in fact, a high calcium intake decreased the risk of symptomatic kidney stones. Surprisingly, intake of animal protein was directly associated with the risk of stone formation.