- While many kidney stones contain calcium, excessive calcium intake alone typically isn't the main cause of stone formation.
- A diet low in calcium can actually increase the risk of kidney stones, especially when consuming oxalate-rich foods like beets and almonds.
- High sodium consumption is more likely to contribute to kidney stones than taking calcium supplements.
Most kidney stones are primarily composed of calcium. Up to 85% of these stones contain the mineral, with many stone-prone individuals having elevated calcium levels in their urine.
The presence of excessive calcium doesn't necessarily mean you should stop your calcium supplements, as several dietary factors influence kidney stone risk. Getting the correct amount of calcium can be more beneficial than harmful for your kidneys.
After digestion, waste products are expelled and processed by the kidneys through urine. When the volume of water passing through the kidneys is insufficient, these waste particles can clump together and crystallize into stones.
The most common type of stone forms when calcium bonds with oxalate, an antinutrient found in plant-based foods. This can occur due to high urine levels of oxalate or calcium.
This problem is especially frequent in individuals with idiopathic hypercalciuria, a condition characterized by excessively high urinary calcium levels despite normal dietary intake. People suffering from hyperparathyroidism also have increased blood calcium levels, which raises the risk of developing kidney stones.
For those without hypercalciuria, exceeding the recommended calcium intake may slightly increase the likelihood of forming kidney stones. Nonetheless, factors like inadequate hydration and excessive salt consumption are far more significant contributors to this risk according to Amy Yau, MD, a nephrologist at The Ohio State University Wexner Medical Center.
Certain patients might be advised to take calcium supplements for bone health or other reasons. If they already obtain ample calcium from their diet, these supplements could push them beyond the recommended 1,000-1,300 milligrams daily intake, with excess calcium possibly being excreted in urine.
However, excessive calcium consumption is not typically the primary cause of kidney stones, as per Melanie Betz, RD, a dietitian and author of The Kidney Dietitian blog.
“If you have calcium oxalate kidney stones, it's important to ensure that you're getting enough calcium,” Betz said.
Research has indicated that diets low in calcium are associated with a higher risk of forming kidney stones. When consuming large quantities of high-oxalate vegetables and fruits like beets and almonds, adequate calcium intake is crucial for binding oxalates and allowing their excretion through stool rather than urine stone formation.
“Ensuring proper calcium consumption is the most effective way to lower urinary oxalate levels when they are high,” Betz said.
Amy Yau, notes that she first advises reducing salt intake rather than calcium for patients with calcium-oxalate stones.
“The primary reason for elevated urinal calcium is not excessive calcium or calcium supplements—it's from consuming too much salt,” she explained.
Excessive salt intake causes the body to retain sodium and reabsorb calcium. However, when salt intake is too high, this forces the kidneys to excrete both components in urine, which can lead to stone crystallization, Yau detailed.
Staying well-hydrated helps flush out calcium and oxalates before they can bind together in the kidneys.
The body absorbs dietary calcium more efficiently than from supplements.
“As a society, we tend to rush into using supplements. We often overlook that nutrition can come from food, and quite often, as in this situation, it's actually better,” Betz said.
Dairy products are typically the best dietary calcium sources due to their excellent absorption rates. Calcium-rich plant-based foods like almond milk and leafy greens sometimes contain oxalates which can limit calcium absorption.
Still, Betz advises against avoidance of oxalates; a strict low-oxalate diet may cause the loss of beneficial nutrients like potassium, magnesium, phytate, and fiber—all of which reduce the risk of kidney stones.
In some cases, taking calcium supplements can be beneficial. People who have undergone gastric bypass surgeries or suffer from Crohn's disease and similar digestive ailments often absorb excess oxalates, raising their stone risk. These individuals might benefit from calcium supplements to bind with oxalates and lower stone formation risks.