Van Loo-Bouwman CA, West CE, van Breeman RB, Zhu D, Siebelink E, Versloot P, Hulshof PJM, van Lieshout M, Russel FGM, Schaafsma G, Naber THJ. 2009. Vitamin A equivalency of -carotene in healthy adults: limitations of the extrinsic dual-isotope dilution technique to measure matrix effect. British Journal of Nutrition 101:1837-1845.