1. Arroyave G, Aguilar JR, Flores M & Guzman MA (1979): Evaluation of Sugar Fortification with Vitamin A at the National Level. pp 1–82. Washington, DC: Pan American Health Organization.
2. Bahl R, Bhandari N, Taneja S & Bhan MK (1997): The impact of vitamin A supplementation on physical growth of children is dependent on season. Eur. J. Clin. Nutr. 51, 26–29.
3. Clausen SW & McCoord AB (1938): The carotenoids and vitamin A of the blood. J. Pediatr. 13, 635–650.
4. Corner G (1989): dSURVEY User Manual. Australia: Helkorn Pty. Ltd..
5. Dean AG, Arner TG, Sangam S, Sunki GG, Friedman R, Lantinga M, Zubieta JC, Sullivan K & Smith DC (2000): Epi Info 2000. A Database, and Statistics Program for Public Health Professionals for use on windows 95, 98, NT, and 2000 computers. Centers for Disease Control and Prevention, Atlanta, Georgia, USA.