Effect of high-dose vitamin C on hepatic cytochrome P450 3A4 activity.

Study Objectives: To investigate the effect of high-dose vitamin C on cytochrome P450 (CYP) 3A4 activity, and to evaluate possible sex-specific effects on CYP3A4 activity.

Design: Single-center longitudinal study.

Setting: Tertiary- and specialty-care teaching hospital.

Subjects: Fourteen healthy Caucasian adult volunteers (seven men, seven women).

Intervention: Subjects self-administered vitamin C 500 mg twice/day for 14 days.

Measurements And Main Results: Hepatic CYP3A4 activity was measured by using the erythromycin breath test on days 1 (baseline) and 15. Overall, no significant effect of vitamin C on CYP3A4 activity was observed. Sex and baseline results were significant predictors of changes in CYP3A4 activity. In men, mean activity increased by 21.9% (95% confidence interval -3.88-47.6%). The effect in women was not consistent.

Conclusion: Sex and baseline CYP3A4 activity appeared to influence the effect of vitamin C on CYP3A4 activity.