Gout is a type of arthritis common in people with high levels of uric acid, hyperurecemia, in their blood. Gout manifests as painful inflammation in one or more joints such as the big toe, knee or ankle joints. High uric acid level in blood does not cause gout in every person but it is generally associated with gout. Blood uric acid level greater than 9 mg/dL is associated with ten-fold increase in risk of gout.
Hyperurecemia is associated with consumption of high purine foods and alcohol, intake of certain drugs and health conditions such as diabetes, kidney disease and obesity. Therefore, among other approaches, gout experts recommend adoption of diet and lifestyle regime to reduce uric acid level in blood through either or combination of lowering purine intake or faster removal of uric acid from the blood.
On-going research also suggests dietary vitamin or supplementation may help reduce serum uric acid level and subsequently lower risk of gout. Vitamin C (ascorbic acid) has been demonstrated to reduce uric acid production and increase its excretion, and lower its level in blood.
A systematic review of human studies, first-authored by Stephen Juraschek and published in the June 23, 2011 issue of Arthritis Care and Research journal, on the effect of vitamin C supplement intake on serum uric acid level found that vitamin C supplementation was associated with serum uric acid level reduction in 8 out of 13 studies.
The 13 studies, randomized controlled trials from the last 30 years, were conducted on a total of 556 human subjects, 20 to 81 years old men and women, healthy and with certain disease conditions, with serum uric acid level ranging 2.9 to 7.0 mg/dL (SI: 172.5 – 416.4 μmol/L). The reported vitamin C supplements dosage were 200 mg/d to 2000mg/d, with a median of 500 mg/d. Recommended dietary allowance (RDA) for vitamin C for adult women and men is 75 - 90 mg/d.
In overall, the vitamin C supplementation effected 0.35 mg/dL (SI: 20.8 μmol/L) serum uric acid reduction. The effect was greater on subjects with a baseline serum uric acid level greater or equal to 4.85 mg/dL (SI: 288.5 μmol/L). On these subjects, the serum uric acid level was reduced by 0.78 mg/dL, (SI: 46.4 μmol/L).
The authors of the review study suggest that further studies with more evaluation criteria and subjects with higher baseline serum uric acid level be carried out. They concluded even though their review of the 13 studies indicates vitamin C intake results in modest uric acid level reduction, more studies are needed to definitively link vitamin C supplementation with decrease of uric acid level and risk of gout.
Stephen P. Juraschek, Edgar R. Miller, Allan C. Gelber (2011). Effect of oral vitamin C supplementation on serum uric acid: A meta-analysis of randomized controlled trials. Arthritis Care Res (Hoboken). June 13 2011. doi: 10.1002/acr.20519.