High regular doses of vitamin C may increase risk of kidney stones

According to a new Swedish study, men who regularly take vitamin C supplements but not multivitamins may be at a higher risk of developing kidney stones.

The observational study documented cases of kidney stones among 23,355 men with no history of kidney stones who consumed either no dietary supplements or supplementswith vitamin C (ascorbic acid) over the course of 11 years (1). The risk of kidney stones in vitamin C-takers was compared with the risk among men who did not take any supplements and in men who took only multivitamins. The study results indicated that men who took vitamin C supplements – more than 7 tablets containing the typical dose of around 1000 mg per week – were twice as likely to develop kidney stones as men who did not take any dietary supplements or men who regularly used multivitamins.

The researchers suggested that both the dose of vitamin C and the combination of nutrients with which it is ingested could play an important role in the risk of kidney stones. However, the findings could not prove that the vitamin itself triggered the stones to form. The results would need to be confirmed by further studies. While the relationship between regularly high doses of vitamin C and kidney stones is not clear, some ex-perts suggest the recommended vitamin C intake should be raised to 200 mg/day for adults.

1. Thomas L. D. K. et al. Ascorbic acid supplements and kidney stone incidence among men: a prospective study. JAMA Internal Medicine. Published online February 2013.