Kidney stones are a common cause of primary care and emergency department visits in the United States. Vitamin C, also called ascorbic acid, is an antioxidant found in citrus fruits and certain vegetables. High dose vitamin C is sometimes recommended to promote health, but may elevate the risk of kidney stone formation.
Types of Kidney Stones
There is more than one type of kidney stone. The most common is the calcium type, composed of calcium oxalate or calcium phosphate, which makes up about 80 percent of all kidney stones. Other kidney stones are composed of struvite, uric acid or cystine. A person can have more than one type of stone at the same time.
How Kidney Stones Form
It is important to know the mechanisms by which stones form to understand the potential effect of vitamin C. Calcium stones form when calcium oxalate or calcium phosphate crystals become concentrated in the urine. Low urine pH and high levels of calcium and oxalate in the urine promote calcium stone formation. Struvite stones form after a urinary tract infection with a type of bacteria that produces urease, which increases the urine pH. Uric acid stones form when the levels of uric acid in the urine are high, which occurs in patients with gout. Cystine stones are rare and have a genetic cause.
Reasons Vitamin C May Increase Kidney Stone Risk
Vitamin C is converted to oxalate, which is subsequently excreted in the urine. In high doses, it has been postulated to lower the pH in the urine. Over time, these factors can increase the risk of calcium stone formation. Due to its potential pH-lowering properties, Vitamin C has sometimes been used to prevent the formation of struvite stones.
Reasons Vitamin C May Not Cause Kidney Stones
In a 2003 study in the "Journal of Urology," the authors measured the urine pH and oxalate concentrations after giving vitamin C to both normal patients and calcium stone-forming patients. Although they found that the oxalate concentration increased in patients given vitamin C, there was no change in the urine pH concentration. Furthermore, the study does not prove that the administration of vitamin C ultimately leads to stone formation. Unfortunately, a recent, definitive study on the role of vitamin C in the development of kidney stones does not exist.
Safe Levels of Vitamin C
In the book "Campbell-Walsh Urology," Dr. Paul Pietrow acknowledges that the evidence for the risk of vitamin C leading to kidney stones is inconclusive. However, he recommends that patients with a propensity for the formation of calcium stones should limit vitamin C to less than 2 grams per day. In "Reviews in Urology," Dr. Dean Assimos recommends that since high-dose vitamin C does not appear to alter the urine pH, it should not be used to prevent struvite stones.
References
- "Journal of Urology"; Effect of ascorbic acid consumption on urinary stone risk factors; Oliver Traxer, MD et al; 2003
- "Campbell-Walsh Urology"; Evaluation and Medical Management of Urinary Lithiasis; Alan Wein, MD (Editor), Paul Pietrow, MD and Glenn Preminger MD; 2007
- "Reviews in Urology"; Vitamin C Supplementation and Urinary Oxalate Excretion; Dean G Assimos, MD; 2004
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