title: Thymus Activity, Vitamin D, and Respiratory Infections in Adolescent Swimmers.
abstract: BACKGROUND
  Several studies have identified associations between low vitamin D concentrations and risk of upper respiratory infections (URI). T lymphocytes have a major anti-viral role, are affected by vitamin D metabolism, and may mediate the link between vitamin D and URIs. Competitive swimmers have a relatively high rate of URIs, alongside a high prevalence of low vitamin D concentration.
  
  
  OBJECTIVE
  To examine the associations linking T cell receptor excision circles (TREC, markers of thymus activity), circulating 25(OH)D concentrations and the effect of vitamin D supplementation, and URI symptoms in young competitive swimmers.
  
  
  METHODS
  We tested 82 adolescent swimmers for serum 25(OH)D and TREC concentrations and found that 55 had vitamin D insufficiency. Randomized supplementation of either vitamin D3 or placebo was given for 12 winter weeks. URI symptoms were recorded weekly. The associations between TREC copy numbers, vitamin D and URI burden were examined.
  
  
  RESULTS
  TREC concentrations decreased with the participants' age (r = -0.346, P = 0.003), with no significant between-gender difference. TREC concentrations did not materially differ among subjects with normal, insufficient or deficient vitamin D status, and were not affected by vitamin D supplementation. No significant correlations were found between TREC levels or their changes during the study period, and mean URI severity or duration.
  
  
  CONCLUSIONS
  Thymus activity, represented by higher TREC levels, was not related to vitamin D concentrations or status, and was not affected by vitamin D supplementation in adolescent swimmers. TREC concentrations were not associated with URI severity or duration in this population.
authors.forename: Inbal
authors.initials: I
authors.lastname: Mayan
authors.forename: Raz
authors.initials: R
authors.lastname: Somech
authors.forename: Atar
authors.initials: A
authors.lastname: Lev
authors.forename: Avner H
authors.initials: AH
authors.lastname: Cohen
authors.forename: Naama W
authors.initials: NW
authors.lastname: Constantini
authors.forename: Gal
authors.initials: G
authors.lastname: Dubnov-Raz
mesh_terms: D000293:Adolescent; D002648:Child; D002762:Cholecalciferol / Q000008:administration & dosage*; D019587:Dietary Supplements; D005260:Female; D006801:Humans; D008297:Male; D012141:Respiratory Tract Infections / Q000453:epidemiology*; D012720:Severity of Illness Index; D013550:Swimming; D013950:Thymus Gland / Q000378:metabolism*; D014807:Vitamin D / Q000031:analogs & derivatives* / Q000097:blood
chemical_list: D014807:Vitamin D; D002762:Cholecalciferol; C104450:25-hydroxyvitamin D