Vitamin C status is inversely related to quercetin bioavailability in young adults

Defining factors regulating quercetin (Q) bioavailability may help to understand its cardioprotective activities. We conducted a pharmacokinetic trial to investigate whether vitamin C status affects Q bioavailability in young adults. Participants (n = 7M/5F, 21.3 ± 3.2 y, 22.8 ± 4.9 kg/m 2 ) ingested 1095 mg Q aglycone with a standardized meal. Plasma vitamin C and endotoxin were measured prior to ingesting Q whereas Q and its methylated metabolites, isorhamnetin (ISO) and tamarixetin (TAM), were measured at timed intervals for 24 h. Maximal plasma Q (1.21 ± 0.66 μM) occurred at 6.0 ± 3.3 h, Q half‐life was 12.2 ± 7.2 h, and inter‐subject variability of Q AUC 0–24 h (15.51 ± 6.44 μM * h) was 42%. Plasma Q AUC 0–24 h was related to AUC 0–24 h of ISO and TAM (r = 0.91–0.96), indicating that greater Q bioavailability increases its biotransformation. Plasma vitamin C was inversely related to the AUC 0–24 h of Q, ISO, and TAM (r = −0.58 to −0.72), suggesting that poor vitamin C status increases Q bioavailability and its propensity to be methylated. Vitamin C was also inversely related to endotoxin (r = −0.58), and endotoxin was correlated with total Q (Q + ISO + TAM; r = 0.50), suggesting that poor vitamin C status increases Q bioavailability by increasing intestinal permeability. Future dietary interventions are warranted to investigate whether alterations in vitamin C status regulate Q bioavailability. Funded by Donaghue Nutrition Research Program.