title: High vitamin D status in younger individuals is associated with low circulating thyrotropin.
abstract: BACKGROUND
  Vitamin D is an immunomodulator and may affect autoimmune thyroid diseases. Vitamin D has also been shown to influence thyrocytes directly by attenuating thyrotropin (TSH)-stimulated iodide uptake and cell growth. However, it is unclear how vitamin D status is related to TSH at the population level. The goal of the present study was to investigate the relationship between vitamin D status and TSH levels according to thyroid autoantibodies in a population-based health survey in Thailand.
  
  
  METHODS
  A total of 2582 adults, aged 15-98 years, were randomly selected according to the geographical region from the Thailand 4th National Health Examination Survey sample. By study design, the sexes were equally represented. Serum levels of 25-hydroxyvitamin D [25(OH)D], TSH, the thyroid peroxidase antibody (TPOAb), and the thyroglobulin antibody (TgAb) were measured in all subjects.
  
  
  RESULTS
  The mean age was 55.0±0.4 (SE) years. In subjects positive for serum TgAb, serum TSH levels were higher, whereas total serum 25(OH)D levels were lower. In addition, the prevalence of vitamin D insufficiency in TgAb-positive subjects was significantly higher than that observed in TPOAb- and TgAb-negative subjects, whether based on cutoff values of 20 or 30 ng/mL: 8.3% vs. 5.6%, p<0.05; or 47.6% vs. 42.0%, p<0.05, respectively. However, vitamin D status was not associated with positive TPOAb and/or TgAb after controlling for sex and age. To explore the probable interaction between vitamin D status and age on serum TSH, analyses were performed according to age tertiles; it was found that higher 25(OH)D levels were independently associated with lower TSH, but only in subjects in the lowest age tertile.
  
  
  CONCLUSIONS
  This population-based study showed that high vitamin D status in younger individuals is associated with low circulating TSH.
authors.affiliation: Department of Medicine, Ramathibodi Hospital, Mahidol University, Bangkok, Thailand. laor.cha@mahidol.ac.th
authors.forename: La-or
authors.initials: LO
authors.lastname: Chailurkit
authors.forename: Wichai
authors.initials: W
authors.lastname: Aekplakorn
authors.forename: Boonsong
authors.initials: B
authors.lastname: Ongphiphadhanakul
mesh_terms: D015652:25-Hydroxyvitamin D 2 / Q000097:blood* / Q000276:immunology; D000293:Adolescent; D000328:Adult; D000367:Age Factors; D000368:Aged; D000369:Aged, 80 and over; D001323:Autoantibodies / Q000097:blood; D002112:Calcifediol / Q000097:blood* / Q000276:immunology; D005260:Female; D006801:Humans; D007155:Immunologic Factors / Q000097:blood; D007453:Iodide Peroxidase / Q000276:immunology; D008297:Male; D008875:Middle Aged; D009752:Nutritional Status; D013785:Thailand; D013954:Thyroglobulin / Q000276:immunology; D013972:Thyrotropin / Q000097:blood* / Q000276:immunology; D055815:Young Adult
chemical_list: D001323:Autoantibodies; D007155:Immunologic Factors; C056626:thyroid microsomal antibodies; D015652:25-Hydroxyvitamin D 2; D013972:Thyrotropin; D013954:Thyroglobulin; D007453:Iodide Peroxidase; D002112:Calcifediol