Scientists have been debating the relationship between vitamin C supplements and kidney stones for decades. In the 1970s the New England Journal of Medicine published heated correspondence about this controversy.
Now Swedish investigators have weighed in with a study of vitamin C supplementation in middle aged and elderly men. Nearly 1000 took large doses of vitamin C regularly. They were matched with about 22,000 men who did not take vitamin C pills. They were followed for more than a decade.
Those who took vitamin C were twice as likely to develop kidney stones than those who did not swallow supplements, but the absolute risk was small. Over the 12 years of the study, roughly 3.4% of vitamin C takers suffered stones whereas 1.8% of the matched controls experienced kidney stones.
In Sweden, the usual dose of vitamin C is around 1,000 mg. This amount could lead to oxalic acid crystals forming in the kidneys. The authors conclude that men should be warned that high-doses of vitamin C may double their risk of kidney stones.
[JAMA Internal Medicine, online, Feb. 4, 2013]