Dietary calcium and the risk of kidney stone disease.

Most kidney stones made of calcium, most commonly calcium oxalate.  Many men and women with calcium kidney stones have increased amount of calcium in the urine when evaluated with 24-hour urine collection.

It is intuitive to think that decreasing the amount of calcium in the diet would lead to decreased risk of kidney stone formation.

The reality is different.  Multiple studies have demonstrated that people who have lower dietary intake of calcium  are at higher risk for kidney stone formation.  In fact studies have looked at both dietary calcium intake from milk products and other forms of calcium in the diet.  These studies consistently demonstrate that people with lower calcium intake in the diet are at much higher risk for having calcium kidney stones than people with normal or higher level of calcium intake from dietary sources.

It is believed that calcium in diet decreases kidney stone formation by binding oxalate in the gut and preventing absorption of oxalate.

For all patients with kidney stones adequate intake of calcium in the diet is recommended. Calcium restricted diet is not recommended because counter-intuitively it is associated with higher risk of forming calcium stones.

It is important to note that supplementary calcium taken in pill forms (for example calcium and vitamin D supplements used for postmenopausal women) is associated with higher risk of kidney stone formation. It is possible that this is caused by a high load of calcium in the gut which leads to high gut absorption of calcium. It is likely that when calcium is consumed in food (milk products, etc) calcium has a better chance of binding oxalate and preventing absorption of both oxalate and calcium. It is possible that taking calcium supplements with food may minimize the chances of increased stone formation.

To summarize:

• Do NOT restrict the amount of calcium in your diet.
• Taking supplemental calcium in pill form seems to increase risk of stone formation. If you need to take it for other reasons (osteoporosis, etc), it may be beneficial to take it in close proximity with food intake.
• Do restrict Sodium intake (SALT)

References:

http://www.ncbi.nlm.nih.gov/pubmed/23535174