High doses of vitamin C supplements linked to kidney stones

NEW research from Karolinska Institutet in Sweden shows that men who regularly take high doses of vitamin C supplements (ascorbic acid, approximately 1,000mg per tablet) run a higher risk of developing kidney stones. The study*, published in the JAMA Internal Medicine (Online First), did not however observe an increased risk between kidney stones and multivitamins – which contain lower concentrations of vitamin C.

The research is based on data from a large population-based study of men in Sweden, who were monitored for 11 years. A total of 23,355 men were identified who had no history of kidney stones and who took either no dietary supplements or supplements in the form of vitamin C only. During the study period, 436 of the participants developed kidney stones that required medical attention.

Ascorbic acid use was associated with a statistically significant two-fold increased risk. However, multivitamin use was not associated with kidney stone risk (risk ratio, 0.86), according to the study results.

The results of the study indicate that men who take vitamin C supplements are twice as likely to develop kidney stones as men who do not take any dietary supplements. The risk was also found to increase with the frequency of vitamin C supplement use. The regular use of multivitamins was not found to be associated with the risk of kidney stones.

The researchers believe that both the dose and combination of nutrients with which the vitamin C is ingested are important. For this reason, the observed increase in risk does not apply to a normal dietary intake of vitamin C from fruit and vegetables. In Sweden, the RDI for vitamin C is 75 mg; the vitamin C content of supplements is commonly 1,000 mg per tablet, which is a considerably higher dose than which is obtained through food.

“Because the risk associated with ascorbic acid may depend both on the dose and on the combination of nutrients with which the ascorbic acid is ingested, our findings should not be translated to dietary vitamin C,” the study notes.

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