Relative contribution of α-carotene to postprandial Vitamin A concentrations in healthy humans after carrot consumption

Abstract

Background: Asymmetric a-carotene, a proVitamin A carotenoid, is cleaved to produce retinol (Vitamin A) and a-retinol (with negligible Vitamin A activity). The Vitamin A activity of a-carotene- containing foods is likely overestimated because traditional analytic methods do not separate a-retinol derivatives from active retinol. Objective: This study aimed to accurately characterize intestinal a-carotene cleavage and its relative contribution to postprandial Vitamin A in humans after consumption of raw carrots. Design: Healthy adults (n = 12) consumed a meal containing 300 g raw carrot (providing 27.3 mg β-carotene and 18.7 mg α-carotene). Triglyceride-rich lipoprotein fractions of plasma were isolated and extracted, and a-retinyl palmitate (aRP) and retinyl palmitate were measured over 12 h postprandially via highperformance liquid chromatography-tandem mass spectrometry. The complete profile of all α-retinyl esters and retinyl esters was measured at 6 h, and total absorption of α- and β-carotene was calculated. Results: aRP was identified and quantified in every subject. No difference in preference for absorption of β- over a-carotene was observed (adjusting for dose, 28% higher, P = 0.103). After absorption, β-carotene trended toward preferential cleavage compared with a-carotene (22% higher, P = 0.084). A large range of proVitamin A carotenoid conversion efficiencies was observed, with a-carotene contributing 12-35% of newly converted Vitamin A (predicted contribution = 25.5%). In all subjects, a majority of a-retinol was esterified to palmitic acid (as compared with other fatty acids). Conclusions: α-Retinol is esterified in the enterocyte and transported in the blood analogous to retinol. The percentage of absorption of a-carotene from raw carrots was not significantly different from β-carotene when adjusting for dose, although a trend toward higher cleavage of β-carotene was observed. The results demonstrate large interindividual variability in a-carotene conversion. The contribution of newly absorbed a-carotene to postprandial Vitamin A should not be estimated but should be measured directly to accurately assess the Vitamin A capacity of α-carotene- containing foods.