Camellia sinensis in asymptomatic hyperuricemia: A meta-analysis of tea or tea extract effects on uric acid levels

Abstract

Flavanols of Camellia sinensis exhibit uric acid (UA) lowering effect, through the modulation of both xanthine oxidase and urate excretion. In order to investigate the potential benefit of Camellia Sinenis products in asymptomatic hyperuricemia, a meta-analysis of long-term Randomized Controlled Trials (RCT) with tea or tea extract has been conducted. From 20 human intervention studies selected only 5 RCT (13 interventions) were suitable for meta-analysis (n = 472). The current "normal" range set for hyperuricemia fails to identify patients with potential metabolic disorders. Therefore on the basis of the literature data, we fixed cut-off limits for UA baseline levels of 4.5 mg/dl for women, 6.1 mg/dl for men, and 5.5 mg/dl for studies involving mixed populations. Statistically significant effects were not found, but subgroup analysis revealed that the Pooled Estimate effect was different in subjects with baseline levels under [MD (95% CI): 0.1078 (-0.0528 to 0.2684)] and over the cut-off [MD (95% CI): -0.0239 (0.3311 to 0.2833)]. However, due to the low number of RCT and to the lack of data on bioavailability, it is difficult to draw any firm conclusion and more studies are needed to establish if tea flavanols could be useful in asymptomatic hyperuricemia treatment.

Antioxidants from black and green tea: from dietary modulation of oxidative stress to pharmacological mechanisms

“…As shown in Table , theaflavins and catechins inhibit xanthine oxidase (XO) activity and UA production in vitro : theaflavin 3,3′‐O‐digallate (10 −6 M) and EGCG (10 −7 M) act as competitive inhibitors (Aucamp et al , ; Lin et al , ). Despite the effect of theaflavins and catechins as XO inhibitors, in a meta‐analysis reviewing human intervention studies that measured UA after tea products, no significant differences were observed between BT, GT and GTE (Peluso et al , ). However, it must be taken into account that many studies had UA as secondary outpoint and did not consider the fact that the normal range of UA differs in males and females.…”

“…Apart from their antioxidant activity, tea flavanols could also have other activities of pharmacological interest, such as the ability to lower glucose (Liu et al , ; Zheng et al , ), lipid (Zheng et al , ; Hartley et al , ; Onakpoya et al ., ) and uric acid (UA) (Peluso et al , ) concentrations. These activities could be mediated by their effects on various enzymes and transporters (Peluso et al ., ).…”

Total Antioxidant Capacity in beta-thalassemia: A systematic review and meta-analysis of case-control studies

“…The data extracted from each study included the first-author's name, year of publication, country of the study performed, ethnicity, subject characteristics, type of BT, comorbidities, method of evaluation of TAC and other markers of plasma redox status. For each study with more than one beta-thalassemic group, we divided the control group evenly according to the number of disease groups [14]. When the data were presented as standard error of means (SEM), standard deviation (SD) was obtained by multiplying SEM by the square root of the sample size [14].…”

“…For each study with more than one beta-thalassemic group, we divided the control group evenly according to the number of disease groups [14]. When the data were presented as standard error of means (SEM), standard deviation (SD) was obtained by multiplying SEM by the square root of the sample size [14]. Data extraction was performed independently by two reviewers (H.M. and G.D.) to ensure uniformity.…”

“…Mean difference (MD) and confidence intervals 95% (CI 95%) were calculated by the random effect model (DerSimonian & Laird) for continuous data. Statistical heterogeneity was assessed by using the  2 statistic and Egger's weighted regression statistics [14]. Symmetry or asymmetry of funnel plots and trim-andfill sensitivity analysis were used to determine the presence of publication bias [14].…”