Vitamin C added little to the urate-lowering effect of standard gout treatment and was clinically ineffective when used alone, according to a small randomized trial published online May 16 in Arthritis & Rheumatism.
According to lead author Lisa Stamp, PhD, from the University of Otago in Christchurch, New Zealand, the study objective was to determine whether reductions in serum urate reported in a previous article by Huang et al in healthy control participants given vitamin C (500 mg/day) would also occur in patients with gout. If that were the case, the authors reasoned, then vitamin C might be a useful addition to standard gout treatment with allopurinol or probenecid.
"In gout patients, our study suggests there is no clinical benefit in terms of lowering uric acid levels with 500 mg/day of vitamin C," Dr. Stamp told Medscape Medical News. "There have been suggestions that vitamin C supplementation would be helpful in gout. Most of the previous work that led to these suggestions has been based on studies in healthy subjects. While there may be a decreased risk of developing gout in people with higher vitamin C intake, our study is the first to show that vitamin C is not an effective treatment for gout."
The researchers recruited 40 patients with gout who had urate levels greater than the American College of Rheumatology treatment target level of 0.36 mmol/L (6 mg/100 mL). The 20 patients already taking allopurinol either received an additional 500-mg dose of vitamin C daily or a higher dose of allopurinol. The 20 patients who had not been taking allopurinol at baseline either started taking allopurinol or began taking vitamin C (500 mg/day). The primary outcome measure was reduction in serum urate at week 8.
The researchers found that vitamin C increased serum ascorbate levels but did not lower serum urate levels enough to be clinically significant. At 8 weeks, serum urate levels were reduced in those who began taking allopurinol, unchanged in those who began taking vitamin C, reduced in those who added more allopurinol to their baseline urate-lowering therapy, and unchanged in those who added vitamin C to their baseline urate-lowering therapy.
"Vitamin C 500 mg will probably not do any harm but also [may] not be of any benefit in terms of lowering uric acid. I would not recommend it as a treatment for gout, but patients may wish to take it for other reasons," Dr. Stamp said.
The contrast between the results for patients with gout in this study and those for normal participants in the earlier study by Huang et al raises questions about the power of the study, about the vitamin C dose tested, and about ways that patients with gout might differ from normal patients in processing vitamin C.
"As the authors noted, this is a pilot study of 40 gout patients. In contrast, the referenced randomized trial by Huang et al that tested the same dose of 500 mg of daily vitamin C supplementation had 184 participants (without gout). This makes readers wonder whether the smaller sample size (ie, the lower 'power' of the study) could be one of the potential reasons underlying the null results obtained from the current study," Hyon Choi, MD, from the Section of Rheumatology and the Clinical Epidemiology Unit, Boston University Medical School, Massachusetts, told Medscape Medical News. Dr. Choi, who was not involved in this study, has also studied the effect of vitamin C on the risk of developing gout.
According to Dr. Stamp, the 500 mg/day dose of vitamin C was chosen because that dose was used in the previous studies in normal participants.
"The dose of 500 mg/day vitamin is consistent with our previous study including 1387 men. In this study, we found a significant association between greater intakes of vitamin C intake and lower serum uric acid concentrations with a plateau of 500 mg/day. However, it is important to test the association between vitamin C and serum uric acid with different doses in the same population and then test whether there is a dose–response relationship between vitamin C intake and serum uric acid reduction," Xiang Gao, MD, PhD, told Medscape Medical News. Dr. Gao, who is assistant professor and research scientist at Harvard Medical School and Harvard School of Public Health and associate epidemiologist at Brigham and Women's Hospital, Boston, Massachusetts, was not involved in the study.
The study authors, Dr. Choi, and Dr. Gao have disclosed no relevant financial relationships.
Arthritis Rheum. Published online May 16, 2013. Abstract
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Cite this: Gout: No Help From Vitamin C - Medscape - May 16, 2013.