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

Am J Clin Nutr. 2017 Jul;106(1):59-66. doi: 10.3945/ajcn.116.150821. Epub 2017 May 17.


Background: Asymmetric α-carotene, a provitamin A carotenoid, is cleaved to produce retinol (vitamin A) and α-retinol (with negligible vitamin A activity). The vitamin A activity of α-carotene-containing foods is likely overestimated because traditional analytic methods do not separate α-retinol derivatives from active retinol.Objective: This study aimed to accurately characterize intestinal α-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 α-retinyl palmitate (αRP) and retinyl palmitate were measured over 12 h postprandially via high-performance 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: αRP was identified and quantified in every subject. No difference in preference for absorption of β- over α-carotene was observed (adjusting for dose, 28% higher, P = 0.103). After absorption, β-carotene trended toward preferential cleavage compared with α-carotene (22% higher, P = 0.084). A large range of provitamin A carotenoid conversion efficiencies was observed, with α-carotene contributing 12-35% of newly converted vitamin A (predicted contribution = 25.5%). In all subjects, a majority of α-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 α-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 α-carotene conversion. The contribution of newly absorbed α-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. This trial was registered at as NCT01432210.

Keywords: bioconversion; carrot; vitamin A; α-carotene; α-retinol.

MeSH terms

  • Adult
  • Biological Availability
  • Carotenoids / blood
  • Carotenoids / pharmacokinetics*
  • Daucus carota / chemistry*
  • Diterpenes
  • Enterocytes / metabolism
  • Esterification
  • Female
  • Humans
  • Intestinal Absorption*
  • Male
  • Meals
  • Plant Extracts / blood
  • Plant Extracts / pharmacokinetics
  • Postprandial Period*
  • Provitamins
  • Retinyl Esters
  • Vitamin A / analogs & derivatives
  • Vitamin A / blood*
  • Young Adult
  • beta Carotene / blood
  • beta Carotene / pharmacokinetics


  • Diterpenes
  • Plant Extracts
  • Provitamins
  • Retinyl Esters
  • beta Carotene
  • Vitamin A
  • retinol palmitate
  • Carotenoids
  • alpha-carotene

Associated data