• Mostafa Qorbani, Mahdavi GorabiArmitaAChronic Diseases Research Center, Endocrinology and Metabolism Population Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran., Hanieh-Sadat Ejtahed, Nazli Namazi, Maliheh Khoramdad, Ramin Heshmat, Elham Kazemian, and Roya Kelishadi.
• Non-communicable Diseases Research Center, Alborz University of Medical Sciences, Karaj, Iran; Chronic Diseases Research Center, Endocrinology and Metabolism Population Sciences Institute, Tehran University of Medical Sciences, Tehran, Iran.
• Nutrition. 2021 Oct 1; 90: 111307.

ObjectivesThe reference values to determine vitamin A and D deficiency may vary based on ethnicity, age, and region of residence. The aim of this study was to determine the reference interval of circulating vitamin A and D levels among Iranian children and adolescents based on sex, age, and region of residence.MethodsThis nationwide cross-sectional study was performed with 2596 students 7 to 18 y of age from the CASPIAN-V (Childhood and Adolescence Surveillance and Prevention of Adult Non- communicable disease) study. A parametric method was used to define the age-specific reference values by obtaining smooth centile curves and explicit formulae for the centile estimates and SD scores for both sexes and regions of residence.ResultsSignificant differences were found between the residents of rural and urban regions in terms of serum 25-hydroxyvitamin D [25(OH)D] and retinol concentration (P < 0.05). Boys (27 ± 8 versus 26.04 ± 10, P = 0.009). Children ages 7 to 12 y had higher serum 25(OH)D concentration than 13- to 18-y-old adolescents (26.96 ± 8 versus 26.04 ± 10, P = 0.007). The estimated reference interval for circulating 25(OH)D levels corresponding to the range between the 5th and 95th percentiles were 11.45 to 48.40 ng/mL in boys and 9.51 to 47.69 ng/mL in girls. Estimated reference intervals for serum retinol concentration among boys and girls corresponding to the 5th and 95th percentiles were 0.58 to 3.38 and 0.58 to 4.52, respectively. There were significant variations in both retinol and 25(OH)D concentrations across different age groups.ConclusionThis study established the reference intervals for circulating 25(OH)D and retinol levels in Iranian adolescents and children in different age groups based on sex and region.Copyright © 2021 Elsevier Inc. All rights reserved.

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