title: The effect of vitamin A supplementation on thyroid function in premenopausal women.
abstract: OBJECTIVE
  Vitamin A and its retinoid derivates play an important role in regulation of normal growth and development. Vitamin A has been shown to regulate thyroid hormone metabolism and inhibit thyroid-stimulating hormone (TSH) secretion via down regulation of TSH-β gene expression; however, the effect of vitamin A on thyroid function in obese individuals who are at higher risk of subclinical hypothyroidism is still unclear. In the present study we investigate the impact of vitamin A supplementation on thyroid function in obese women.
  
  
  METHODS
  A 4-month randomized, double blind controlled trial was conducted among 84 healthy women aged 17-50 years old: 56 were obese (body mass index [BMI] 30-35 kg/m(2)) and 28 were nonobese (BMI 18.5-24.9 kg/m(2)). Obese women were randomly allocated to receive either vitamin A (25,000 IU/d retinyl palmitate) or placebo. Nonobese women received vitamin A. At baseline and 4 months after intervention, serum concentrations of TSH, total thyroxine (T4), total triiodothyronine (T3), retinol-binding protein (RBP), and transthyretin (TTR) were measured.
  
  
  RESULTS
  Baseline concentrations of thyroid hormones, RBP and TTR were not significantly different between groups. Vitamin A caused a significant reduction in serum TSH concentrations in obese (p = 0.004) and nonobese (p = 0.001) groups. Serum T3 concentrations also increased in both obese and nonobese vitamin A-treated groups (p < 0.001). Serum T4 decreased in all 3 groups after treatment. The results showed a significant reduction in serum RBP in the obese group after vitamin A supplementation (p = 0.007), but no significant change was seen in serum TTR.
  
  
  CONCLUSIONS
  Serum TSH concentrations in vitamin A-treated subjects were significantly reduced; therefore, vitamin A supplementation might reduce the risk of subclinical hypothyroidism in premenopausal women.
authors: Department of Community Nutrition, Faculty of Health and Nutrition, Tabriz University of Medical Sciences, Tabriz, Iran.
authors: Mahdieh Abbasalizad
authors: MA
authors: Farhangi
authors: Seyyed Ali
authors: SA
authors: Keshavarz
authors: Mohammadreza
authors: M
authors: Eshraghian
authors: Alireza
authors: A
authors: Ostadrahimi
authors: Ali Akbar
authors: AA
authors: Saboor-Yaraghi
mesh_terms: D000293:Adolescent; D000328:Adult; D015992:Body Mass Index; D019587:Dietary Supplements; D004311:Double-Blind Method; D015536:Down-Regulation; D005260:Female; D006801:Humans; D007037:Hypothyroidism / Q000503:physiopathology / Q000517:prevention & control; D008875:Middle Aged; D009765:Obesity / Q000188:drug therapy; D011228:Prealbumin / Q000032:analysis; D017697:Premenopause / Q000187:drug effects; D012177:Retinol-Binding Proteins / Q000032:analysis; D013961:Thyroid Gland / Q000187:drug effects* / Q000378:metabolism; D013972:Thyrotropin / Q000097:blood; D037322:Thyrotropin, beta Subunit / Q000032:analysis; D013974:Thyroxine / Q000097:blood; D014284:Triiodothyronine / Q000097:blood; D014801:Vitamin A / Q000008:administration & dosage*; D055815:Young Adult
chemical_list: D011228:Prealbumin; D012177:Retinol-Binding Proteins; D037322:Thyrotropin, beta Subunit; D014284:Triiodothyronine; D014801:Vitamin A; D013972:Thyrotropin; D013974:Thyroxine