Abstract and Introduction
Objective The objective of this study was to investigate the hypouricemic effects of green tea extract (GTE) in healthy individuals.
Methods This study comprised 1-week control, 2-week interventional, and 1-week follow-up periods. Participants were assigned randomly at the interventional period to consume GTE at 2 (GTE2), 4 (GTE4), or 6 (GTE6) g/d. Levels of serum uric acid (SUA), uric acid clearance, and serum antioxidant power (using trolox equivalent antioxidant capacity assay) were measured at both ends of each study period.
Results Of 30 participants, 11, 11, and 8 received GTE2, GTE4, and GTE6, respectively. After 2 weeks of consumption, the mean SUA level tended to decrease in all groups, with no statistical significance. Serum uric acid reduction was greatest in GTE2 (from 4.81 ± 0.81 mg/dL to 4.64 ± 0.92 mg/dL, 3.53%). Uric acid clearance decreased significantly in GTE2 (from 11.37 ± 6.41 mL/min per 1.73 m2 to 7.44 ± 2.74 mL/min per 1.73 m2, 34.56%, P < 0.05) and GTE4 (from 8.36 ± 3.41 mL/min per 1.73 m2 to 5.78 ± 2.33 mL/min per 1.73 m2, 30.86%, P < 0.05). Serum antioxidant capacity (TEAC) increased significantly in GTE6 (from 32.77 ± 3.39 mg/mL to 35.41 ± 3.17 mg/mL, 8.06%, P < 0.05). There was no significant change in creatinine clearance. Gastrointestinal adverse events were common, but usually mild, with no medical treatment required.
Conclusions Green tea extract may modestly lower SUA level and decreases uric acid clearance. Green tea extract also significantly elevated serum antioxidant capacity with a positive dosage effect. The effect of GTE on SUA in healthy individuals was short term. The effects of GTE on urate handling in patients with hyperuricemia or gout need to be determined.
Hyperuricemia is a risk factor in the development of gout, which is the most common cause of acute inflammatory arthritis in men. Consumption of alcohol and a high purine diet such as red meat and seafood can increase the serum uric acid (SUA) level, whereas consumption of dairy products, coffee, vitamin C, and cherries can reduce it.[1,2]
Green tea (Camellia sinensis), a common drink among Japanese people, contains a high amount of polyphenolic antioxidants, particularly catechins. The principal catechins in green tea are catechin (C), epicatechin, epigallocatechin, epicatechin gallate, and epigallocatechin gallate (EGCG). Epigallocatechin gallate is the major catechin, with up to 13% dried weight of green tea leaves. Green tea has a strong antioxidant property by acting through multiple mechanisms, including antilipid peroxidation, free-radical scavenging, metal sequestration, and inhibition of several enzymes including xanthine oxidase (XO). Several studies have demonstrated that catechins inhibit XO activity in vitro.[5–8] In a study by Aucamp et al. the inhibition constant (Ki) of EGCG was comparable to that of allopurinol, a commonly used XO inhibitor (0.76 vs 0.30 μmol).
The effect of green tea on XO activity in humans was demonstrated in a study by Panza et al. They observed an increase in XO activity after exercise in the control group, but such an increase was not seen in participants who consumed green tea. This suggested that consumption of green tea could inhibit XO activity in humans. A decrease in the level of SUA after consuming green tea extract (GTE) was observed in a number of human trials.[10–12] Nevertheless, these studies were not designed primarily to evaluate the effects of GTE on SUA level. This study therefore was designed to evaluate the hypouricemic effects of green tea in healthy individuals.
J Clin Rheumatol. 2014;20(6):310-313. © 2014 Lippincott Williams & Wilkins