The Impact of Diet, Including Dairy Products and Ascorbate, on the Serum Uric Acid
The serum urate level depends on the balance between dietary intake, endogenous synthesis and net uric acid excretion. The annual incidence of gout directly correlates with serum urate level.[3*,4*,20,21,22,23] As such, patients with gout have typically been advised to avoid foods rich in purines, such as meat and seafood. Until recent studies by Choi and his co-workers, however, the relationship between the intake of purine-rich foods, the level of serum uric acid and the incidence of gout had not been studied prospectively.
Recently, the specific relationship between the intake of purine-rich foods, protein and dairy products, and the level of serum uric acid was evaluated using NHANES III data. Data analyzed were from a prospective cohort[4*] of 14 809 participants (6932 men and 7877 women) selected from 1988 to 1994 to simulate a representative sample of the non-institutionalized civilian population. The mean serum uric acid was 5.32 mg/dl and 18% had hyperuricemia. Serum uric acid increased significantly as a function of meat and fish intake, with the multivariate odds ratios (ORs) of 1.37 (95% CI 1.05-1.80) and 1.58 (95% CI 1.07-2.34), respectively. Total protein intake, however, was not associated with an increase in serum uric acid. In fact, high-protein diets have been associated with an increased urinary excretion of uric acid and may actually lower serum uric acid. Therefore, patients should be cautioned against using the protein content of foods as a surrogate marker of purine content.
Several studies have suggested a protective effect of low-fat dairy product consumption on serum uric acid levels. Consistent with prior studies, a significant inverse association was also noted between the intake of dairy and serum uric acid level in the NHANES III (OR 0.66; 95% CI 0.48-0.89). The dairy proteins casein and lactalbumin were thought to lower serum uric acid level by inducing urinary excretion of uric acid.[25,26,27] Such direct uricosuric effects of the proteins in dairy products are relatively weak, as illustrated in a study of nuns after menopause.
Previous studies[28,29] have suggested a significant uricosuric effect of vitamin C. Recently, the effect of vitamin C on serum uric acid level was evaluated in a double-blind placebo-controlled study[30*] of 184 participants who received either placebo or 500 mg per day of vitamin C for 2 months. Both groups had similar intake of protein, purine-rich foods and dairy products at baseline. The serum uric acid level, however, was lowered only in the vitamin C group. Among those who had hyperuricemia at baseline (uric acid greater than 7 mg/dl), vitamin C supplementation resulted in a mean uric acid reduction of 1.5 mg/dl (P = 0.0008, adjusted for age, sex and baseline serum uric acid and ascorbic acid level). It has been postulated that vitamin C may decrease serum uric acid by both increasing renal secretion and decreasing renal re-absorption of uric acid through competitive binding activities. Despite this potential benefit of vitamin C supplementation, its role in the prevention and management of gout has not been established.
Curr Opin Rheumatol. 2006;18(2):193-198. © 2006 Lippincott Williams & Wilkins
Cite this: Recent Developments in Diet and Gout - Medscape - Mar 01, 2006.