Which previous studies have suggested that vitamin C moderates gout risk?
A previous study in by Choi et al in the USA showed that people with a higher vitamin C intake have a lower risk of gout. There are also studies in healthy volunteers that suggest that vitamin C supplements reduce blood uric acid levels.
What mechanism did these studies propose for moderation of gout risk by vitamin C supplementation?
It is thought that vitamin C increases the excretion of uric acid in the urine.
The exact mechanism is not known, however, it is thought to be something to do with the way the kidneys excrete uric acid.
There is some evidence that vitamin C might also reduce production of uric acid as well but the major mechanism is thought to be through increasing excretion through the kidneys.
Please can you outline your recent research into vitamin C supplementation in gout patients?
We recruited gout patients who had blood uric acid levels greater than the treatment target level of 0.36 mmol/L (6 mg/100 mL).
Of the 40 participants with gout, 20 patients taking allopurinol were given an additional 500 mg dose of vitamin C daily or had the dose of allopurinol increased, while another 20 patients were either started on allopurinol or vitamin C (500 mg/day).
We analyzed blood levels of vitamin C (ascorbate), creatinine and uric acid at baseline and week eight.
What were the findings of your study?
Our study showed that a modest vitamin C dose (500mg/d) for eight weeks did not lower urate levels to a clinically significant degree in gout patients, but did increase blood levels of ascorbate (vitamin C).
Did your research involve patients taking vitamins pills or adjusting their diet to increase their vitamin C intake?
Patients were given vitamin C pills.
Do you think your results would have differed if patients had increased their vitamin C intake by diet modification rather than taking vitamin C pills?
No. The dose of vitamin C we gave was higher than the daily recommended intake and the blood levels of ascorbate (vitamin C) increased suggesting that patients were receiving adequate amounts.
Were you surprised by the results of your study?
Not really. The degree of change in uric acid levels is similar to that seen in other studies. The amount of change is unlikely to have any significant clinical benefit for patients with gout.
Are the results of your research conclusive or is further research needed to confirm whether vitamin C is beneficial to gout patients?
Higher doses of vitamin C could be studied, however the risks of higher doses needs to be considered.
The dose we gave is already above the recommended daily dose and the blood levels reached a point where increasing them further was unlikely to have any extra effect.
Although your research looked at the effects of vitamin C supplementation on uric acid levels, do you think there may be other benefits of gout patients taking fruits containing vitamin C? For example, are fresh cherries and cherry juice effective at lowering uric acid levels?
Cherries have been reported to lower uric acid levels in women. They have also been reported to reduce the number of gout attacks. The mechanism by which cherries exert these effects is not entirely clear. It has been suggested that cherries increase uric acid excretion via the kidneys and may lower urate production. There are also other anti-inflammatory chemicals in cherries that may have an effect. The amount of vitamin C in cherries is probably not high enough to have any effect.
Why do many patients fail to reach appropriate urate levels despite taking current treatments?
The two most common reasons patients don’t reach appropriate urate levels are not taking the medicines that lower uric acid levels regularly and that the dose of the medicine is too low.
How was your research funded?
The research was funded by the Health Research Council of NZ.
Do you have any plans to research other alternative therapies for gout?
We have plans to look at the effects of omega three fats in acute gout.
There are two things you need to do when you are treating gout. Firstly, you need to treat the acute attacks as they come, secondly, in the long term you need to lower the uric acid to prevent the attacks from coming.
Omega three fats work like a natural anti-inflammatory. The study, which is being led by one of my colleagues in Wellington, will look at whether we could treat those acute attacks of gout by omega three fats rather than using anti-inflammatory drugs. Anti-inflammatory drugs can have quite a lot of side effects.
Where can readers find more information on research into gout treatments?
Patients can look on the clinical trial registry web sites for studies on gout medicines.
Readers can find our research paper here: http://onlinelibrary.wiley.com/doi/10.1002/art.37925/abstract;jsessionid=CBF67F2B57C8F7B5DF8F6E2C58A29DBB.d03t03?systemMessage=Wiley+Online+Library+will+be+disrupted+on+18+May+from+10%3A00-12%3A00+BST+%2805%3A00-07%3A00+EDT%29+for+essential+maintenance
About Prof. Lisa Stamp
Professor Lisa Stamp is a Rheumatologist at the University of Otago, Christchurch and Christchurch Hospital.
She is director of the Canterbury Rheumatology Immunology Research Group and the University of Otago Arthritis Research Theme.
She received a University of Otago Early Career Award for Distinction in Research in 2009 and the Rowheath Trust Award and Carl Smith Medal for Research in 2011.
Professor Stamp has an active clinical role in adult rheumatology. Her research interests include individualization of drug treatments in gout and rheumatoid arthritis.
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