Vitamin C, or ascorbic acid, is essential for your health. Many animals can manufacture vitamin C in their cells, but humans must obtain it from their diet. Vitamin C's benefits and potential uses have been the subject of a great deal of scientific scrutiny, and claims that high doses of vitamin C can cure colds or prevent cancer are still hotly debated. Although vitamin C's place in your overall health is undisputed, high dosages of this vital nutrient could potentially contribute to specific medical conditions, such as kidney stones.
Kidney Stones
Kidney stones are crystallized mineral deposits that your body forms from waste products in your urine. According to scientists at the University of Kansas Medical Center, about 5 percent of men and women in the United States suffer from kidney stones, otherwise known as nephrolithiasis, during their lifetimes. About 70 percent of all kidney stones are composed of calcium oxalate. When the concentration of metabolic by-products in your urine exceeds a certain point, you can form a kidney stone. Then, much like a hailstone, the kidney stone acquires successive layers until it is large enough to begin moving through your urinary tract.
Risk Factors
Anything that decreases urine volume or flow or that increases the levels of waste products in your urine can increase your chances for forming a kidney stone. Higher urine levels of calcium, phosphate, sodium, uric acid and oxalate contribute to stone formation, as do dehydration and alkaline urine. Bowel diseases, obesity, prolonged immobilization, insulin resistance, gout and excess dietary sodium, oxalate and meat have all been linked to an increased risk for nephrolithiasis. In certain individuals, supplemental vitamin C might also contribute to stone formation.
Oxalate Stones
A study published in the December 2004 issue of "Journal of the American Society of Nephrology" suggested that men who consumed more than 1,000 mg of vitamin C daily had a slightly increased risk for forming kidney stones. However, this heightened risk might only pertain to people with a tendency to form oxalate kidney stones. In the December 2008 issue of "Gene Reviews," Dr. Gill Rumsby of the University College London Hospitals recommended that people with primary hyperoxaluria -- a genetic condition that causes increased intestinal absorption and urinary excretion of oxalates -- avoid supplemental vitamin C, because it is metabolized to oxalates in body tissues.
Considerations
Most kidney stones are composed of calcium oxalate. Because vitamin C is metabolized to oxalates in your body, high doses of vitamin C could theoretically increase your risk for forming a kidney stone, particularly if you become dehydrated or acquire any other risk factor for nephrolithiasis. Individuals with primary hyperoxaluria, who already have a higher risk for oxalate kidney stones, should avoid supplemental vitamin C. If you have ever had an oxalate-containing kidney stone, ask your doctor if you should take extra vitamin C.
References
- Linus Pauling Institute at Oregon State University: Vitamin C and the Common Cold
- "American Family Physician"; Medical Management of Common Urinary Calculi; P.K. Pietrow, M.E. Karellas; July 2006
- "Journal of the American Society of Nephrology"; Dietary Factors and the Risk of Incident Kidney Stones in Men: New Insights after 14 Years of Follow-up; E.N. Taylor, et al.; December 2004
- "Gene Reviews"; Primary Hyperoxaluria Type 2; G. Rumsby; December 2008
