xanthines

n.crystalline oxidation product of the metabolism of nucleoproteins; precursor of uric acid; found in many organs and in urine

1. Xanthines such as caffeine can stimulate the central nervous system and improve alertness.
   黄嘌呤类物质（如咖啡因）可以刺激中枢神经系统，增强警觉性。
2. The doctor advised against consuming too many products containing xanthines due to potential health risks.
   医生建议避免过量摄入含有黄嘌呤类物质的产品，因为它们可能带来健康风险。