Vitamin C ups kidney stone risk

Men who take ascorbic acid supplements daily (approximately 1000 mg) were at increased risk for first incident cases of kidney stones (rate difference, 147/100,000 compared with men who do not take ascorbic acid supplements). This represents a dose-dependent, 2-fold increased risk for kidney stone formation.

Laura D.K. Thomas, MSc, from the Institute of Environmental Medicine, Division of Nutritional Epidemiology, Karolinska Institutet, Stockholm, Sweden, and colleagues published the results of their large, population-based prospective cohortstudy online February 4 in JAMA Internal Medicine.

The study was performed in the Cohort of Swedish Men and included 48,850 men aged 45 to 79 years. The authors estimated, but were not able to accurately assess, the dose of vitamin C consumed by the men in the study.

The authors controlled for age, education level, body mass index, tea and coffee use, smoking status, hypertension, and diabetes mellitus. They did not control for dehydration, immobilization, use of loop diuretics, corticosteroids, or vitamin D.

They found high-dose (1000 mg) vitamin C to be associated with a single new kidney stone per 680 high-dose users per year. They found no association between multivitamin use and kidney stone risk (relative risk, 0.86; 95% confidence interval, 0.62 - 1.191).

The study included only men, and the authors note that the results may not be generalizable to women.

In an accompanying editorial, Robert H. Fletcher, MD, from Harvard Medical School in Boston, Massachusetts, discussed the benefits and risks of vitamin supplementation. He began his editorial by describing the original purpose of vitamin supplementation, which was to avoid vitamin-deficiency diseases such as pellagra, rickets, and scurvy. Since that time, however, vitamin supplements have been consumed with the intention of preventing or treating chronic diseases.

Treatment with vitamin C, for example, began in the 1700s as a response to the scurvy experienced by sailors who spent months at sea. In the 1900s, the Nobel Laureate Linus Pauling, PhD, proposed that vitamin C was an effective treatment for the common cold, cancer, and cardiovascular disease. Dr. Pauling's enthusiasm for vitamin C inspired numerous clinical trials that were unable to support the use of vitamin D to prevent mortality.

Recently, evidence has been accumulating that vitamin C supplementation may also be unsafe in that it promotes the formation of kidney stones. Results from the current study are consistent with other studies that have linked vitamin C supplementation and kidney stone formation.

Source: http://www.medscape.com/viewarticle/778769?nlid=27860_1301&src=wnl_edit_dail&uac=129655SZ