The debate over Vitamin C contributing to the formation of kidney stones has raged for decades. And just when it seems the question has been settled a new study pops up to renew the debate. Vitamin C was first postulated to be a cause for calcium oxalate kidney stones, the most common kind of kidney stone, because ascorbic acid (vitamin c) can be converted to oxalate, which when combined with calcium can accrete into kidney stones. A review of the literature reveals misconceptions and laboratory misinterpretations that solidified this belief; it turns out ascorbic acid in urine samples was converted to oxalic acid outside the body when the sample was being tested.[i]

Most naturopaths and doctors using high therapeutic doses of vitamin C with their patients would likely agree that the incidence of kidney stones in those patients is low. Most studies tend to back up this conception. An early study looked at 4-day diet recalls of men with and without kidney stones and found those afflicted were more likely to have higher dietary ascorbic acid.[ii] Several subsequent population studies have looked at the impact of vitamin C on kidney stone formation. Out of five studies looking at dietary intake of ascorbic acid in large populations of men and women (over 200,000 individuals in total) four of the studies showed no increased risk on kidney stones with levels of ascorbic acid at 1500 to 2000 mg daily.[iii]^{,[iv],[v],[vi]} One of the studies that followed men over a period of 14 years did show an age-related increase in symptomatic kidney stones with daily intake of 100 mg or more of vitamin C.[vii] Recently, a laboratory control trial looked again at oxalate absorption and formation in the body as related to vitamin c intake of 2000 mg daily, compared between groups of people who tended to develop kidney stone and those who did not. The results of the study did show a significant increase in oxalate absorption and formation in the stone –forming individuals.[viii]

So what can one conclude from all these studies and can we finally lay this debate to rest? The overwhelming evidence points to little to no effect of vitamin C intake, at levels between 1000 and 2000 mg daily, on kidney stone formation. However there is conflicting evidence, especially in older adult males, that vitamin C can contribute to kidney stones. Finally, among those who are predisposed to form kidney stones, higher dietary intake of vitamin C does seem to increase oxalate levels, hence a risk of increased kidney stones. That means that for most of us, vitamin C will not likely contribute to kidney stone formation. But, caution is advised among those that have a history of forming calcium-oxalate kidney stones, and lowered intake of vitamin C may be warranted in this population.

<!--EndFragment-->