Many kidney stone formers, especially women with kidney stones, question whether to stop or reduce their calcium intake. Despite the fact that calcium is a major component of 75% of stones, excessive calcium intake is very rarely the cause of stone formation. In fact, several studies have shown that restricting calcium intake in most stone formers actually increases the number of stones they develop. This appears to happen because when less calcium is ingested, it becomes easier for oxalate (which normally binds with calcium in the gut) to be absorbed. Higher levels of oxalate in the urine then lead to an increase in stone risk.
What contains calcium?
Calcium is found in many food types. It is most concentrated in dairy products, such as milk, ice cream, and cheese. It is also present in non-dairy products, such as broccoli and almonds. Many foods are also fortified with calcium, including soy milk and breads.
Calcium is commonly given as a supplement, either by itself or as part of a multivitamin. By itself, it is most commonly in the form of calcium carbonate. Other forms included calcium citrate and coral calcium.
I’m a woman on calcium supplements to help prevent osteoporosis, do I need to stop or reduce my calcium pills?
If you can, it is better for you to get your calcium from dietary sources instead of calcium supplements. This is because supplements can increase your risk of stones slightly. In a large study of over 35,000 women given calcium with vitamin D or placebo, the women on the calcium supplements were 17% more likely to develop stones than those on placebo (Wallace et al, Am J Clin Nutr 2011). Dietary sources of calcium such as dairy have the opposite effect and lowers your risk of stones. In a large study of almost 100,000 female nurses between 27 and 44 years old and without a history of prior stones, researchers found that the nurses with the highest calcium intake had a lower risk of developing a stone than those with the lowest calcium intake. (Curhan et al, Arch Intern Med, 2004). Many other studies have come to similar conclusions and our general recommendation is for most patients to maintain a normal dietary calcium intake but to try to avoid calcium supplements if possible. This is in contrast to older recommendations previously given to kidney stone formers to reduce their calcium intake.
I don’t tolerate dairy and need to take supplements. What about different types of calcium supplements?
The two most common types of calcium supplements are calcium carbonate and calcium citrate. Calcium carbonate tends to be less expensive while calcium citrate is more easily digested and can be taken on an empty stomach. Calcium citrate costs more and has a lower amount of calcium in each pill, requiring more of it to be taken.
Calcium citrate is preferred for stone formers because it has the stone friendly benefit of also increasing urinary citrate concentrations. Citrate is an inhibitor of stones, which makes it more difficult for calcium based stones to form.
Researchers have found that taking calcium supplements with meals appears to be better than taking supplements by themselves in regards to stone formation. This may be due to the availability of the calcium taken at mealtime to bind oxalate, a stone promoting substance.
*updated 10/16/12 with new information on calcium supplements.