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Oxalate Kidney Stones & Supplements

Jun 30, 2011 | By Kimberly Rienecke
Oxalate Kidney Stones & Supplements
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If you take a calcium supplement, you may be at risk for developing kidney stones, recent research suggests. Approximately 80 percent of kidney stones are formed from calcium and of these, 80 percent are derived from calcium oxalate, according to a 2006 article by the Princeton Hypertension Nephrology Associates. While some studies have found no correlation with stone formation, others have suggested the timing of supplementation may be of importance.

Formation of Kidney Stones

The kidneys are responsible for filtering wastes and water from your blood, as well as for creating urine. Kidney stones form when crystals within your urine harden. These crystals develop from chemicals in urine, the most common being calcium oxalate. Calcium is a mineral found in your bones as well as in certain foods. Oxalate is produced by your body and is also found in the certain foods. Normally, calcium binds to oxalate in the intestines. However if the level of oxalate is high, it is absorbed into the bloodstream and then excreted into the urine. Excess oxalate in the urine may then combine with calcium and crystalize, resulting in the formation of stones.

Risk of Oxalate Stone Formation

Research regarding the effect of calcium on oxalate stone formation is somewhat mixed. While some studies suggest that calcium supplements actually discourage the formation of oxalate stones, others have reported the opposite. Researchers in a 2001 study published in the "Journal of Clinical Pathology" discovered that calcium supplements reduced the excretion of oxalate by 9.2 percent and increased urinary calcium by 10.2 percent. Despite this, the level of urine calcium oxalate, as determined by the calcium times oxalate product, actually decreased over a period of six months. The authors attribute this finding to reduced levels of vitamin D, which promotes the absorption of calcium. In contrast to these findings, a 2011 study in the "American Journal of Clinical Nutrition" found that calcium and vitamin D supplements increased oxalate stone formation by 17 percent. This study, however, may be limited by the fact that calcium supplements without vitamin D were not tested, so it is difficult to determine the exact etiology of stone formation.

Timing of Calcium Supplements

The timing of calcium supplements, not the supplements themselves, may be responsible for oxalate kidney stones, Thai researchers report in a 2004 study in "Kidney International." Authors of the study found that administration of calcium supplements at bedtime resulted in a substantial rise in urinary calcium oxalate in 32 male Thai Navy privates . This finding was not represented in participants taking a calcium supplement with meals. The authors propose that the oxalate in food binds to calcium within the intestines, thereby reducing the amount of oxalate that is absorbed into the bloodstream and subsequently excreted into the urine.

Recommended Intake

The National Kidney and Urologic Diseases Information Clearinghouse, or NKUDIC, recommends limiting calcium intake to 800 milligrams a day if you have a history of calcium oxalate stones. In accordance with the findings of several studies, the NKUDIC also recommends consuming calcium supplements with meals to prevent the formation of calcium oxalate stones. Since diets rich in oxalate are also associated with an increased risk of stone formation, foods high in oxalate content should be avoided, including spinach, nuts, rhubarb and wheat bran.

References

Article reviewed by GlennK Last updated on: Jun 30, 2011

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