title: High provitamin A carotenoid serum concentrations, elevated retinyl esters, and saturated retinol-binding protein in Zambian preschool children are consistent with the presence of high liver vitamin A stores.
abstract: BACKGROUND
  Biomarkers of micronutrient status are needed to best define deficiencies and excesses of essential nutrients.
  
  
  OBJECTIVE
  We evaluated several supporting biomarkers of vitamin A status in Zambian children to determine whether any of the biomarkers were consistent with high liver retinol stores determined by using retinol isotope dilution (RID).
  
  
  METHODS
  A randomized, placebo-controlled, biofortified maize efficacy trial was conducted in 140 rural Zambian children from 4 villages. A series of biomarkers were investigated to better define the vitamin A status of these children. In addition to the assessment of total-body retinol stores (TBSs) by using RID, tests included analyses of serum carotenoids, retinyl esters, and pyridoxal-5'-phosphate (PLP) by using high-pressure liquid chromatography, retinol-binding protein by using ELISA, and alanine aminotransferase (ALT) activity by using a colorimetric assay.
  
  
  RESULTS
  Children (n = 133) were analyzed quantitatively for TBSs by using RID. TBSs, retinyl esters, some carotenoids, and PLP differed by village site. Serum carotenoids were elevated above most nonintervened reference values for children. α-Carotene, β-carotene, and lutein values were >95th percentile from children in the US NHANES III, and 13% of children had hypercarotenemia (defined as total carotenoid concentration >3.7 μmol/L). Although only 2% of children had serum retinyl esters >10% of total retinol plus retinyl esters, 16% of children had >5% as esters, which was consistent with high liver retinol stores. Ratios of serum retinol to retinol-binding protein did not deviate from 1.0, which indicated full saturation. ALT activity was low, which was likely due to underlying vitamin B-6 deficiency, which was confirmed by very low serum PLP concentrations.
  
  
  CONCLUSIONS
  The finding of hypervitaminosis A in Zambian children was supported by high circulating concentrations of carotenoids and mildly elevated serum retinyl esters. ALT-activity assays may be compromised with co-existing vitamin B-6 deficiency. Nutrition education to improve intakes of whole grains and animal-source foods may enhance vitamin B-6 status in Zambians.
authors.affiliation: Interdepartmental Graduate Program in Nutritional Sciences, University of Wisconsin-Madison, Madison, WI;
authors.forename: Stephanie
authors.initials: S
authors.lastname: Mondloch
authors.affiliation: Interdepartmental Graduate Program in Nutritional Sciences, University of Wisconsin-Madison, Madison, WI;
authors.forename: Bryan M
authors.identifier: http://orcid.org/0000-0003-1781-9242
authors.initials: BM
authors.lastname: Gannon
authors.affiliation: Interdepartmental Graduate Program in Nutritional Sciences, University of Wisconsin-Madison, Madison, WI;
authors.forename: Christopher R
authors.initials: CR
authors.lastname: Davis
authors.affiliation: Tropical Diseases Research Centre, Ndola, Zambia;
authors.forename: Justin
authors.initials: J
authors.lastname: Chileshe
authors.affiliation: National Food and Nutrition Commission of Zambia, Lusaka, Zambia; and.
authors.forename: Chisela
authors.initials: C
authors.lastname: Kaliwile
authors.affiliation: National Food and Nutrition Commission of Zambia, Lusaka, Zambia; and.
authors.forename: Cassim
authors.initials: C
authors.lastname: Masi
authors.affiliation: University of Florida, Gainesville, FL.
authors.forename: Luisa
authors.initials: L
authors.lastname: Rios-Avila
authors.affiliation: University of Florida, Gainesville, FL.
authors.forename: Jesse F
authors.initials: JF
authors.lastname: Gregory
authors.affiliation: Interdepartmental Graduate Program in Nutritional Sciences, University of Wisconsin-Madison, Madison, WI; sherry@nutrisci.wisc.edu.
authors.forename: Sherry A
authors.initials: SA
authors.lastname: Tanumihardjo
mesh_terms: D015415:Biomarkers / Q000097:blood / Q000378:metabolism; D002247:Carbon Isotopes; D002338:Carotenoids / Q000009:adverse effects / Q000097:blood*; D002648:Child; D002664:Child Nutritional Physiological Phenomena; D002675:Child, Preschool; D015331:Cohort Studies; D004032:Diet / Q000009:adverse effects / Q000208:ethnology; D005260:Female; D006801:Humans; D006986:Hypervitaminosis A / Q000175:diagnosis* / Q000208:ethnology / Q000209:etiology / Q000378:metabolism; D007201:Indicator Dilution Techniques; D008099:Liver / Q000378:metabolism*; D008297:Male; D054839:Retinol-Binding Proteins, Plasma / Q000032:analysis*; D012423:Rural Health; D015854:Up-Regulation; D014801:Vitamin A / Q000031:analogs & derivatives* / Q000097:blood / Q000378:metabolism; D014802:Vitamin A Deficiency / Q000175:diagnosis / Q000208:ethnology / Q000378:metabolism / Q000517:prevention & control; D015024:Zambia
chemical_list: D015415:Biomarkers; D002247:Carbon Isotopes; C101326:RBP4 protein, human; D054839:Retinol-Binding Proteins, Plasma; D014801:Vitamin A; D002338:Carotenoids
keywords: Zambia; plant carotenoids; pyridoxal-5′-phosphate; retinol; retinol isotope dilution; school-age children; α-carotene; β-carotene