Effect of Consumption of Cocoa-Derived Products on Uric Acid Crystallization in Urine of Healthy Volunteers

Abstract

The purpose of this study was to determine the effects of consumption of different cocoa-derived products on uric acid crystallization in urine of 20 healthy volunteers. Participants were requested to select the specific diet that they wished to follow during the 12 h prior to collection of urine. The only restriction was that the diet could not include any product with cocoa, coffee, or caffeine. On the first day, each volunteer followed their selected diet, and an overnight 12 h urine sample was collected as the baseline urine. After seven days on an unrestricted diet, each volunteer repeated the same diet with 20 g of milk chocolate, chocolate powder, or dark chocolate during breakfast and another 20 g during dinner. Overnight 12 h urine samples were then collected. Urine volume, pH, oxalate, creatinine, uric acid, theobromine, and a uric acid crystallization test were determined for each sample. The results for all 20 patients show that uric acid crystallization was significantly lower following the consumption of chocolate powder or dark chocolate relative to baseline or following the consumption of milk chocolate. The results indicated that increased concentrations of urinary theobromine reduced the risk of uric acid crystallization.

Keywords: cocoa; theobromine; therapy; uric acid; urolithiasis.

Figure 1

Uric acid crystallization (UAC) test. Six wells of a 12-well plate were used for each sample of urine, with each well containing 5 mL of urine and different amounts of HCL and uric acid. Well #1 had urine alone, well #2 had urine and 50 μL of 2 M HCl (0.1 mmoL H⁺), well #3 had urine and 50 μL of 6 M HCl (0.3 mmol H⁺), well #4 had urine and 750 µg uric acid (375 µL of 2 g/L solution), well #5 had urine, 50 μL of 2 M HCl and 750 µg uric acid, and well #6 had urine, 50 mL 6 M HCl and 750 µg uric acid. Uric acid (AU). + means addition of the specified volume of the solution.

Figure 2

Effect of the consumption of different cocoa products on urinary theobromine concentration (A) and total theobromine excretion in 12 h (B) in each of the 20 volunteers (each colored line corresponds to one of the volunteers), and mean concentration (C) and total excretion in 12 h (D) among all 20 volunteers. An ANOVA repeated measures test indicated significant differences among the four groups in concentration and excretion (p < 0.05). B: basal, MC: milk chocolate, PC: chocolate powder, and DC: dark chocolate.

Figure 3

Representative UAC test results of one volunteer at baseline (B) and after consumption of milk chocolate (MC), chocolate powder (PC), and dark chocolate (DC). Uric acid crystallization was greatly reduced following consumption of chocolate powder or dark chocolate.

Figure 4

UAC test results at baseline (B) and after consumption of milk chocolate (MC), chocolate powder (PC), and dark chocolate (DC). Samples were compared using the Wilcoxon signed-rank test. Boxplots show the median (inner horizontal line), interquartile range (box), 95% confidence interval (vertical lines), and outlier (circle).