Can Taking Too Much Calcium Cause Kidney Stones?

Key Takeaways
Most kidney stones contain calcium, but a high calcium intake alone is not usually the main cause of stones.A low calcium diet can raise kidney stone risk, especially when eating oxalate-rich foods like beets and almonds.High sodium intake is more likely to cause kidney stones than calcium supplements.

Most kidney stones are made of calcium. About 85% of kidney stones contain the mineral, and many people who are prone to stones have high levels of calcium in their urine.

That may not be a reason to toss out your calcium supplements just yet. Several dietary factors can play into kidney stone risk, and getting the right amount of calcium can do more good than harm for your kidneys.

How Calcium and Oxalate Form Stones

After the body processes food, waste products are left behind and flushed out by the kidneys through urine. When not enough water moves through the kidneys, the waste particles can stick together and crystallize into stones.

The most common type of stone forms when calcium binds with oxalate, an antinutrient that is found in plant foods. This can happen when the levels of oxalate or calcium in the urine are too high.

It’s especially common in people with idiopathic hypercalciuria, a condition marked by excessive calcium in the urine despite a normal calcium intake. People with hyperparathyroidism also have elevated blood calcium levels, which puts them at greater risk of developing kidney stones.

For people without hypercalciuria, consuming too much calcium could raise the risk of forming stones. However, other factors, like not drinking enough water or eating too much salt are far more likely to increase that risk, explained Amy Yau, MD, a nephrologist and clinical assistant professor of internal medicine at The Ohio State University Wexner Medical Center.

Excess Calcium Isn’t the Main Cause of Kidney Stones

Some patients may be advised to take calcium supplements for bone health or other reasons. If they get enough calcium from food sources, supplements could put them over the recommended daily intake of 1,000-1,300 milligrams, and the excess may wash out in the urine.

Still, taking too much calcium is not a primary reason people develop kidney stones, said Melanie Betz, RD, a dietitian and author of The Kidney Dietitian blog.

“If you have calcium oxalate kidney stones, you actually want to make sure that you are getting enough calcium,” Betz said.

Getting Enough Calcium Reduces Kidney Stone Risk

Studies have shown that a low calcium diet is associated with a higher risk of forming kidney stones.

When you eat lots of vegetables and fruits that are high in oxalates, like beets and almonds, you need enough calcium to bind with the oxalates and excrete them through your stool. Otherwise, oxalates are absorbed and excreted in urine, where they can form stones.

“Making sure you’re eating enough calcium is the most effective way to get urine levels of oxalate down if they’re even high in the first place,” Betz said.

A High Sodium Diet Is More Likely to Cause Stones

Yau said that when she sees patients with calcium-oxalate stones, she first recommends cutting back on salt rather than calcium intake.

“The biggest reason for having high calcium in the urine is actually not from eating too much calcium or calcium supplements—it’s actually from eating too much salt,” she said.

When you eat moderate amounts of salt, your body retains that sodium and reabsorbs calcium along with it. But too much salt will force your kidneys to wash both out in the urine, where calcium can crystallize into stones, Yau explained.

Staying well hydrated can also help flush out calcium and oxalates before they can bind in the kidneys.

Food-Based Calcium Is Better Than Supplements

The body can more easily retain and use calcium when it’s consumed through food rather than supplements.

“As a society, we are so quick to jump to supplements. It’s almost like we forget that you can get nutrition from food, and many times, this being one of them, it’s actually better,” Betz said.

Dairy is perhaps the best dietary source of calcium because the body absorbs it well. Calcium-rich plant-based foods, like fortified almond milk and leafy greens, often contain oxalates, which limit calcium absorption.

Still, Betz says not to avoid oxalates. Following a strict low-oxalate diet means you may miss out on potassium, magnesium, phytate, and fiber—all of which lower the risk of kidney stones.

There are some instances in which taking a supplement makes sense. People who have undergone gastric bypass surgeries or have Crohn’s disease and other digestive diseases tend to easily absorb oxalate, raising their risk of developing stones. These patients may benefit from taking a calcium supplement to help bind with those oxalates and reduce their stone risk.

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