How Does High Calcium Affect the Kidneys?

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Calcium is the most abundant mineral in your body and is responsible for bone strength, as well as several other functions. While this vitamin is an essential part of your diet, too much can cause problems in your kidneys. Check with your doctor before you begin taking a calcium supplement. It may be unnecessary if you are generally healthy.

Function of Calcium

Approximately 99 percent of the calcium in your body is utilized to keep your bones and teeth strong, supporting structure, says the Office of Dietary Supplements. The remaining calcium throughout your body supports normal nerve function, intracellular signaling so cells can communicate and muscle and heart contractions. In order to support these functions, you need 1,000 mg of calcium from your diet or supplements daily.

Kidneys and Calcium Regulation

Your kidneys play a role in the concentration of calcium in the body. When your blood calcium levels drop, proteins in the parathyroid glands that detect calcium send signals to help secrete parathyroid hormones, or PTH. This hormone helps convert vitamin D into its active form known as calcitriol, explains the Linus Pauling Institute. Calcitriol in the kidneys increases the absorption of calcium. Both PTH and calcitriol help release calcium in bones by activating osteoclasts. These cells help reabsorb calcium, decreasing calcium excretion in the urine, allowing it to be reabsorbed in the kidneys. When calcium is at a normal levels, parathyroid glands cease secretion of PTH and excess calcium is expelled in the urine, which can lead to problems in the kidneys if your calcium level is high.

Calcium and Kidney Stones

The exact cause of kidney stones is unknown; however a condition called hypercalciuria, or excessive calcium in urine, comes with an increased risk for stones. Kidney stones formed from calcium can be either calcium oxalate or calcium phosphate, with calcium oxalate being more common, says the National Kidney and Urologic Diseases Information Clearinghouse. Calcium oxalate stones form when urine is acidic, whereas calcium phosphate stones are a side effect of alkalinic urine. While having too much calcium in your diet can lead to kidney stones, other factors, such as excessive protein and sodium or hydration status, may also increase your chances.

Effects of Diuretics

Diuretics work by forming more urine in the kidneys, increasing the amount of fluid expelled in urine. Since calcium is reabsorbed in the kidneys, taking a diuretic with a high-calcium supplement may increase your risk of hypercalcemia, reports the Linus Pauling Institute. This condition causes high levels of calcium in the blood, possibly leading to an abnormal heart rhythm.