title: The use and interpretation of serum retinol distributions in evaluating the public health impact of vitamin A programmes.
abstract: OBJECTIVE
  Developing countries have adopted universal, high-potency vitamin A (VA) supplementation and food fortification as major strategies to control deficiency, prevent nutritional blindness and reduce child mortality. Yet questions persist regarding how best to measure impact and when to phase out supplementation. The present paper provides guidance on the use and interpretation of serum retinol (SROL) distributions as indicators of both programme impact and adequate VA intake in a population.
  
  
  METHODS
  We reviewed extant data on SROL's response to high-potency VA supplementation and VA-fortified foods in children.
  
  
  RESULTS
  Supplementation virtually eliminates xerophthalmia and reduces child mortality; however, it shifts the SROL distribution only transiently (<2 months). Regular consumption of VA-fortified foods prevents xerophthalmia, lowers mortality and sustainably improves SROL distributions, from which both compliance and public health impact can be inferred.
  
  
  CONCLUSIONS
  Given SROL's limited responsiveness to high-potency VA supplementation, target population coverage remains the preferred performance indicator. However, periodic SROL surveys do reflect underlying dietary risk and can guide programming: low or marginal SROL distributions in areas with high supplementation coverage do not signify programme failure, but rather suggest the need to continue supplementation while working to effectively raise dietary VA intakes. We propose that a sustained rise in the SROL distribution, defined as ≤5 % prevalence of SROL < 0·70 μmol/l among vulnerable population groups in at least two consecutive surveys (≥1 year apart), be used as an indicator of stable and adequate dietary VA intake and status in a population, at which point programmes may re-evaluate the need for continued universal supplementation.
authors.affiliation: Center for Human Nutrition, Department of International Health, Johns Hopkins Bloomberg School of Public Health, 615 North Wolfe Street, Baltimore, MD 21205, USA.
authors.forename: Amanda C
authors.initials: AC
authors.lastname: Palmer
authors.forename: Keith P
authors.initials: KP
authors.lastname: West
authors.forename: Nita
authors.initials: N
authors.lastname: Dalmiya
authors.forename: Werner
authors.initials: W
authors.lastname: Schultink
mesh_terms: D002675:Child, Preschool; D016208:Databases, Factual; D019587:Dietary Supplements; D005527:Food, Fortified; D017408:Guidelines as Topic; D006801:Humans; D007223:Infant; D011634:Public Health; D016032:Randomized Controlled Trials as Topic; D012307:Risk Factors; D014801:Vitamin A / Q000008:administration & dosage* / Q000097:blood*; D014802:Vitamin A Deficiency / Q000150:complications / Q000453:epidemiology* / Q000517:prevention & control*; D014985:Xerophthalmia / Q000209:etiology / Q000517:prevention & control
chemical_list: D014801:Vitamin A