Vitamin C and Kidney Stones | Portland, OR | Lee Dennis, ND

Lee Dennis, ND

Naturopathic Physician


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Vitamin C and Kidney Stones

by Lee Dennis, ND

Posted: September 3, 2013


Ascorbic acid, more commonly known as vitamin C, is a widely available and easily accessible supplement. Because of its availability and popularity as a supplement, it is often taken in amounts much higher than the recommended daily allowance. Though it is generally considered safe in almost any amount, there are some concerns for the risks it may pose in the formation of kidney stones - especially at higher supplemental doses.

The majority of kidney stones are made of calcium oxalate (Chai, Liebman, Kynast-Gales, & Massey, 2004). Ascorbic acid is known to be a precursor for oxalate in the body and high urinary oxalate levels, or hyperoxaluria, are an acknowledged risk factor for calcium oxalate stone formation (Siener, Ebert, Nicolay, & Hesse, 2003). The purpose of this paper is to review the studies that have been done on this topic and identify whether there is an increased risk for incidence of kidney stones with ascorbic acid intake.


Hyperoxaluria is the primary proposed mechanism for ascorbic acid's possible effects on kidney stone formation (Baxman, Mendonca, Heilberg, 2003). Looking at a population of known stone formers, those with hyperoxaluria had a higher incidence of kidney stone passage compared to those with normal oxalate levels (Siener et al., 2003). Early studies looking at the effects of vitamin C intake on oxalate excretion were unreliable due to the possible conversion of urinary ascorbic acid to oxalate spontaneously after the sample was collected or by the oxalate testing procedures specifically (Massey, Liebman, Kynast-Gales, 2005).

Since then, more rigorous studies have been done that have limited this possibility. Along with improved oxalate tests, the main technique used to prevent spontaneous conversion of ascorbic acid to oxalate was preservation with hydrochloric acid (Chai et al., 2004; Massey et al., 2005; Baxman et al., 2003; Siener et al., 2003). Baxman et al. (2003) also tested the effects of EDTA preservation on collected urine samples, but found no difference in oxalate levels between samples collected with and without EDTA. Auer, Auer, and Rogers note that even with the newer oxalate tests and acid preservation, the spontaneous conversion of ascorbic acid to oxalate after collection is still a possibility and should be taken into consideration (as cited in Baxman et al., 2003).


More recent experimental studies have shown that certain individuals respond to ascorbate supplementation with higher urinary excretion of oxalate. Massey et al. (2005) goes so far as to make the distinction between responders and non-responders across both stone forming and non-stone forming groups, meaning that within both groups, certain individuals responded with higher urinary oxalate levels while others did not.

Whether or not that same pattern is present in other studies is unclear. The study conducted by Baxman et al. (2003) only looked at known stone formers and while mean urinary oxalate levels were reported to have increased following ascorbate supplementation of both one and two grams of ascorbate, they did not individualize the results. Chai et al. (2004) studied the effects on both stone formers and non-stone formers. The increase in levels of urinary oxalate after ascorbate supplementation only reached significance within the stone forming group. Again, however, only the mean results were reported and individual variation within the groups was not.

A cross sectional study conducted by Siener et al. (2003) took a different approach. Stone formers were divided into those with hyperoxaluria and those with normal oxalate excretion. Siener et al. (2003) used a twenty-four hour weighed dietary record and reported that the intake of ascorbic acid was greater in stone forming individuals with hyperoxaluria than in those with normal oxalate excretion. It was also reported that stone formers with hyperoxaluria had a higher number of "stone episodes". It is not clear, however, to what degree higher ascorbate ingestion affected endogenous oxalate formation or whether it was more indicative of a plant-based diet containing more dietary oxalates (Siener et al., 2003).

Oxalate Absorption

Although ascorbic acid is usually thought to affect endogenous production of oxalate, another interesting possibility was noted in one study. Ascorbate supplementation not only increased urinary oxalate excretion through endogenous conversion, but also seemed to have the effect of increasing absorption of dietary oxalates in stone formers (Chai et al., 2004). Chai et al. (2004) reported this trend to reach significance between stone forming and non-stone forming females. One possible explanation for this is that excess ascorbic acid may be non-enzymatically converted to oxalate in the alkaline environment of the small intestine (Siener et al., 2003).

Ascorbic Acid, pH and Kidney Stones

Siener et al. (2003) reported a higher urinary pH in stone forming patients with hyperoxaluria. In an alkaline environment with high enough urinary ascorbate levels, ascorbate may be converted to oxalate non-enzymatically (Siener et al., 2003). What is not clear is whether or not ascorbic acid is itself a good urinary acidifier (Baxmann et al., 2003). This is a possibility that could potentially be a limiting factor in the conversion of ascorbic acid to oxalate. Baxmann et al. (2003) tested the effects of ascorbic acid supplementation on pH using both one gram and two grams a day for three days. No significant difference was measured in the pH values with or without ascorbic acid supplementation.

Observational Studies

Several observational studies have been done comparing the rates of ascorbic acid intake and incidence of kidney stones. The results tend to be contradictory showing a positive correlation in some cases and no correlation in others. As mentioned previously, Siener et al. (2003) reports a positive correlation between ascorbic acid intake and hyperoxaluria in stone formers and a higher incidence of kidney stone passage in those with hyperoxaluria.

In a large prospective cohort study conducted by Taylor, Stampfer, and Curhan (2004) similar results were found in men. The study followed a cohort of men with no original history of kidney stones and looked at various dietary factors in relation to the new incidence of kidney stones over a number of years. Multivariate adjustment for other dietary factors revealed a positive association between ascorbic acid intake and the risk for stone formation. Interestingly, in this study it is noted that the association was only found after including potassium in the multivariate adjustment. This is likely because potassium was negatively associated with kidney stone formation and because higher potassium intake was associated with higher ascorbic acid intake (Taylor et al., 2004).

Other studies, however, have shown different results. Curhan, Willett, Speizer, and Stampfer (1999) conducted a similar prospective study with a cohort of women with no previous history of kidney stones. This study reported no association between incidence of kidney stones and ascorbic acid intake after adjusting for age and accounting for other dietary factors. Similarly, a large cross sectional study using data from the second National Health and Nutrition Examination Survey also found no association between serum ascorbic acid levels and incidence of kidney stones (Simon & Hudes, 1999).

Taylor et al. (2004), Curhan et al. (1999), and Simon and Hudes (1999) all had large sample sizes and were therefore more likely to represent the population as a whole. The dietary data, however, was obtained using dietary surveys and therefore may not be very accurate in accounting for ascorbic acid intake. On the other hand, the study done by Siener et al. (2003) was a comparatively smaller sample size, but used weighed dietary records which increases the accuracy considerably. Taylor et al. (2004) and Curhan et al. (1999) also limited the scope of study to only one gender, males and females respectively. Since those results were conflicting, it is unclear as to whether this may stem from a difference in the etiology of kidney stones between males and females or perhaps due to differences in study design and protocol.


Studies have shown a positive correlation between hyperoxaluria and risk for kidney stones. Experimental studies also point towards a positive correlation between urinary oxalate levels and ascorbic acid intake in certain individuals with ascorbic acid having no effect on urinary pH. While it seems the effect on oxalate levels is greatest in the stone forming population, it is possible that ascorbic acid related hyperoxaluria is not necessarily strictly confined to stone formers, nor are all stone formers necessarily affected in such a way by ascorbic acid.

This information is contradicted somewhat by the findings of various observational studies - some finding a correlation between ascorbic acid intake and kidney stone formation and others not. The study by Taylor et al. (2004) indicates that the risk associated with kidney stone formation from ascorbic acid intake may be offset by other dietary factors such as potassium intake. This could be the reason why other studies have shown no correlation.

From what has been surveyed in this paper, it would seem that dietary sources of ascorbic acid are likely safe for most individuals, especially given that ascorbic acid is often found in foods with other micronutrients, such as potassium, that may reduce the risk for stone formation. However, supplemental forms of ascorbic acid may be contraindicated in those with a history of kidney stones or with other risk factors for kidney stones.


Baxmann, A. C., Mendonca, C. D. O., & Heilberg, I. P. (2003). Effect of Vitamin C Supplements on Urinary Oxalate and pH in Calcium Stone-Forming Patients. Kidney International, 63(3), 1066-71.

Chai, W., Liebman, M., Kynast-Gales, S., & Massey, L. (2004). Oxalate Absorption and Endogenous Oxalate Synthesis From Ascorbate in Calcium Oxalate Stone Formers and Non-Stone Formers. American Journal of Kidney Diseases, 44(6), 1060-9.

Curhan, G. C., Willett, W. C., Speizer, F. E., & Stampfer, M. J. (1999). Intake of Vitamins B6 and C and the Risk of Kidney Stones in Women. Journal of the American Society of Nephrology, 10(4), 840-5.

Massey, L. K., Liebman, M., & Kynast-Gales, S. A. (2005). Ascorbate Increases Human Oxaluria and Kidney Stone Risk. The Journal of Nutrition, 135(7), 1673-1677.

Siener, R., Ebert, D., Nicolay, C., & Hesse, A. (2003). Dietary Risk Factors for Hyperoxaluria in Calcium Oxalate Stone Formers. Kidney International, 63(3), 1037-43.

Simon, J. A., & Hudes, E. S. (1999). Relation of Serum Ascorbic Acid to Serum Vitamin B12, Serum Ferritin, and Kidney Stones in US Adults. Archives of Internal Medicine, 159(6), 619-624.

Taylor, E. N., Stampfer, M. J., & Curhan, G. C. (2004). Dietary Factors and the Risk of Incident Kidney Stones in Men: New Insights after 14 Years of Follow-up. Journal of the American Society of Nephrology, 15(12), 3225-32.


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