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).
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.
This work was supported by the BBSRC.