Abstract

Background: NADPH oxidase is a source of reactive oxygen species that may contribute to insulin resistance (IR). Aim: To assess the effect of a single oral dose of vanillin (a putative inhibitor of the enzyme) on IR in humans. Material and Methods: Using a crossover, random, double-blind design, eight lean and 10 obese males ingested 600 mg of vanillin or placebo followed by the ingestion of 75 g of glucose. Serum/plasma glucose, free-fatty acids, insulin, glutathione, C reactive protein concentrations and red blood cell glutathione concentration were determined. Insulin resistance was estimated by the Matsuda index. Results: Under fasting conditions, obese individuals had higher glucose and insulin and lower red blood cell glutathione levels than their lean counterparts (p < 0.01). Serum free-fatty acids, total and oxidized plasma glutathione concentrations were similar in both groups. After glucose ingestion, obese individuals had a lower red blood cell total glutathione concentration and increased plasma oxidized glutathione concentration than their lean counterparts (p < 0.05). In addition, obese participants had a higher level of IR (p < 0.001) and impaired serum free-fatty acid suppression (p < 0.001) than their lean counterparts. Ingestion of vanillin did not modify any of these variables when compared with placebo in obese individuals. In lean volunteers a reduction in Matsuda index was detected when vanillin was administered, compared to placebo (4.3 ± 0.6 and 3.6 ± 0.6 respectively; p < 0.05). Conclusions: IR was ameliorated after vanillin ingestion among lean but not obese participants.