Interindividual variation in aspirin (ASA) metabolism is attributed to concomitant use of drugs or alcohol, urine pH, ethnicity, sex, and genetic variants in UDP-glucuronosyltransferases (UGT). Little is known about the effects of diet.
We evaluated cross-sectionally whether urinary excretion of ASA and its metabolites [salicylic acid (SA), salicyluric acid (SUA) phenolic glucuronide (SUAPG), salicylic acid acyl glucuronide (SAAG) and salicylic acid phenolic glucuronide (SAPG)] differed by UGT1A6 genotype and dietary factors shown to induce UGT. Following oral treatment with 650 mg ASA, urine was collected over 8 h in 264 men and 264 women (21–45 years old).
There were statistically significant differences in metabolites excreted between sexes and ethnicities. Men excreted more SUA; women more ASA (p = 0.03), SA, SAAG and SAPG (p ≤ 0.001 for all). Compared to Caucasians, Asians excreted more ASA, SA and SAAG, and less SUA and SUAPG (p ≤ 0.03 for all); African-Americans excreted more SAAG and SAPG and less SUA (p ≤ 0.04). There was no effect of UGT1A6 genotypes. Increased ASA and decreased SUAPG excretion was observed with increased servings of vegetables (p = 0.008), specifically crucifers (p = 0.05).
Diet may influence the pharmacokinetics of ASA, but effects may be through modulation of glycine conjugation rather than glucuronidation.