Differences Between Calcium Citrate and Calcium Phosphate

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Calcium citrate and calcium phosphate are different forms of calcium. (Image: daizuoxin/iStock/Getty Images)

Calcium is essential for development and maintenance of bones and teeth and for the proper function of the heart, muscles, nerves and other body systems. Calcium is critical in preventing osteoporosis, a condition that is characterized by the breakdown of bone and increased risk of fractures. Calcium citrate and calcium phosphate are common forms of calcium supplements that differ in calcium content, absorption and cost.

Elemental Calcium Content

Eating foods high in calcium and vitamin D plus exercise on a daily basis are important to maintaining healthy bones, according to the National Osteoporosis Foundation. However, many adults do not get enough of these nutrients and physical activity and might require calcium supplements. Calcium citrate and calcium phosphate supplements can increase your dietary intake of calcium. Calcium citrate has about 21 percent elemental calcium; calcium phosphate contains a much lower percentage of elemental calcium. Calcium triphosphate, however, has 39 percent elemental calcium. Taking a higher quantity of calcium phosphate supplements in order to increase the amount of elemental calcium intake can increase your risk of kidney stones. Research by Joan Parks published in "Kidney International" in 2004 showed that the percentage of calcium phosphate in kidney stones has increased for more three decades and that the saturation of calcium phosphate in the stones increases as the intake of calcium phosphate increases. The University of Maryland Medical Center says that your daily total calcium intake from combined dietary and supplemental sources should not exceed 2,500 milligrams. Excessive calcium intake might contribute to the development of kidney stones and inhibit the absorption of iron and zinc.

Calcium Absorption

Your body easily absorbs and digests calcium citrate, and it is a good source of calcium, especially if you are elderly. Calcium citrate does not require extra stomach acid to dissolve and absorb into the body, so you can take it on an empty or full stomach. Magnesium, phosphorous and vitamins D and K are vital for calcium absorption and use in the body. Calcium from calcium phosphate is not easily absorbed, except in the form of calcium triphosphate. Research by Hitomi Kumagai, Ph.D., published in "Biofactors" in 2004 showed that when 92 percent of phosphorous is removed from soybeans, a food with a high content of calcium, intestinal absorption of calcium increases. Take calcium supplements in small doses, less than 500 milligrams per dose with at least four hours between doses so you do not consume excessive amounts, which can lead to developing kidney stones. Drink eight cups of water throughout the day to avoid constipation.


Calcium phosphate costs less than calcium citrate. Calcium phosphate is commonly used to enrich fruit juices, soy milk, rice milk and other foods. Talk with your doctor about the quantities and forms of calcium that are best for you.


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