Gender-related differences in retinol and provitamin A carotenoid metabolism have previously been detected, with higher retinol concentrations in men, and on the contrary, higher β-carotene concentrations in women⁽ Reference Faure and Preziosi ^{1 )}. This reversed relationship suggests a higher β-carotene to retinol conversion rate in males⁽ Reference Faure and Preziosi ^{1 )}. Furthermore, lower conversion efficiency is correlated with BMI in women, but not in men⁽ Reference Tang and Qin ^{2 )}. We investigated retinol metabolism and β-carotene conversion efficiency in 23 female and 19 male volunteers by co-administering 2 mg [¹³C₁₀]-β-carotene and 1 mg [¹³C₁₀]-retinyl acetate. Relative absorption of β-carotene in the first 24 hours represented 11% of total ingested [¹³C₁₀]-β-carotene, with an inter-individual coefficient of variation of 49%. [¹³C₁₀]-β-carotene plasma concentration within the first 24 hours post-dose were significantly inversely related to the ability to convert β-carotene into retinyl-palmitate (r=−0.89; p<0.001). More importantly, significantly higher plasma concentrations of preformed [¹³C₁₀]-retinol and bio-converted [¹³C₅]-retinol were found in men compared to women (Figure 1), although plasma [¹³C₁₀]-β-carotene concentrations were similar between the genders. Interestingly, differences in retinoid concentrations are independent from the ability to cleave [¹³C₁₀]-β-carotene, since both retinyl palmitate/β-carotene and the newly-formed retinoid reference dose ratios are not significantly different between men and women (Figure 1).

Fig. 1. Effect of gender on plasma retinol concentrations and provitamin A conversion efficiency (AUC=Area under the curve for the first 24 hours post-dose).

In summary, our isotope dilution technique revealed that men have higher circulating retinol concentrations compared to women, and that this difference is independent of provitamin A conversion efficiency. We hypothesize that a gender specific effect on metabolic flux between different tissues could explain this difference.