title: Seasonal variations in calcidiol and parathyroid hormone levels in healthy children and adolescents in Navarre, Spain: a cross-sectional study.
abstract: OBJECTIVE
  To analyze the seasonal variations in calcidiol and parathyroid hormone serum levels along a natural year in a paediatric population living in a region of the north of Spain considering a normal nutrition status.
  
  
  METHODS
  A cross-sectional study.
  
  
  METHODS
  Navarra Hospital Complex, Pamplona, Spain.
  
  
  METHODS
  A total of 413 Caucasian individuals (aged 3.1 to 15.4 years): 227 school children (96 males and 131 females) and 186 adolescents (94 males and 92 females), with normal nutritional status.
  
  
  METHODS
  Clinical examination (sex, age, weight, height and body mass index) and blood testing (calcium, phosphate, alkaline phosphatase, calcidiol and parathyroid hormone) during the year 2014.
  
  
  RESULTS
  Calcidiol levels were lower during spring (25.96 ± 6.64 ng/mL) and reached its maximum level in summer (35.33 ± 7.51 ng/mL); parathyroid hormone levels were lower in summer (27.13 ± 7.89 pg/mL) and reached maximum level in autumn (34.73 ± 15.38 pg/mL). Hypovitaminosis D prevalence was 14.3% in summer and 75.3% in spring. Parathyroid hormone levels were compatible with secondary hyperparathyroidism in eight individuals (1.9%). There is a correlation (p < 0.01) between calcidiol and parathyroid hormone (r = -0.336). Logistic regression showed significant increased risk of hypovitaminosis in females (OR:1.63) and adolescents (OR:1.77), and when blood samples taken in autumn (OR:12.22), winter (OR:8.54) and spring (OR:19.72).
  
  
  CONCLUSIONS
  There is a high prevalence of hypovitaminosis D in the paediatric population with a healthy nutrition situation in Navarre, mainly during the months of autumn and winter, and, especially, in spring time. Given the difficulties in maintaining a sufficient amount of body vitamin D content along the year, it should be considered to give vitamin supplements and/or increase the intake of its natural dietary sources or vitamin D fortified foods.
authors.affiliation: Department of Pediatrics, Faculty of Medicine, University of Navarra, Pamplona 31008, Spain; Department of Pediatrics, Navarra Hospital Complex, Pamplona, Spain; Instituto de Investigación Sanitaria de Navarra (IdisNA), Pamplona 31003, Spain.
authors.forename: Teodoro
authors.initials: T
authors.lastname: Durá-Travé
authors.affiliation: Department of Pediatrics, Navarra Hospital Complex, Pamplona, Spain.
authors.forename: Fidel
authors.initials: F
authors.lastname: Gallinas-Victoriano
keywords: Endocrinology; nutrition and metabolism; paediatrics