Urate-lowering effect of calcium supplementation: Analyses of a randomized controlled trial

Objective: To investigate if the gout-protective effect of low-fat dairy products could be attributed to the urate-lowering effect of calcium.

Methods: This is a placebo-controlled trial in which thirty-five adult (aged 18-42 years) female low-calcium consumers (<800 mg/d) were randomized to one of three treatment groups: low calcium breakfast (control, ∼70 mg of calcium/d) -C or high-calcium breakfast (∼770 mg/d) from calcium citrate - CIT or from skim milk - SM, during 45 consecutive days. Breakfasts were matched for potential confounders and were provided as part of an energy-restricted normoprotein diet containing an additional 800 mg of calcium/d. Dual-energy X-ray absorptiometry measurements (body fat assessment) and fasting blood samples (urate, ionic calcium, PTH, and 1,25-(OH)2-D3) were taken at baseline and the end of the experiment.

Clinical trial registration: http://www.ensaiosclinicos.gov.br/ (RBR-7Q2N33).

Results: Despite no significant changes in total body weight/fat, CIT and SM led to a significant reduction in serum urate and ionic calcium, but did not affect PTH and vitamin D concentrations compared to C. CIT and SM reduced baseline serum urate by ∼14% and ∼17%, respectively. There was a trend to a positive correlation between changes in serum urate and changes in ionic calcium on day 45 (r = 0.327, P = 0.055).

Conclusions: Calcium supplementation (770 mg/d from dairy or calcium citrate) reduced serum urate concentrations, suggesting that the gout-protective effect of low-fat dairy consumption is at least partly due to a urate-lowering effect of calcium.