ABSTRACT
T4 and T3, two major hormones of thyroid gland, are responsible for regulation of "basal metabolism" in the body. Thyroid function is regulated primarily by variation in the pituitary TSH. In this study, about four hundred individuals were considered from four Iranian populations. They were selected randomly in their cities; Shiraz, Mashhad, Rasht, and Ilam. Essential family information was asked to achieve native belonging of each person to related population. Blood specimens were collected, by separating serums, freezed serums were transferred immediately to Tehran for hormone assay. Assay of T4 and T3 concentrations was carried out by 'RIA-magnetic' kits and of TSH by 'IRMA-magnetic' kits. Analysis of variance has been taken into account among days of sampling in each city to calculate mean concentrations for T4, T3 and TSH. Analysis of association between age and hormones concentrations in each population was done by the regression and the correlation tests. Significant differences were detected at T4 mean concentration in each of these populations [P=0.0001]. Differences for T3 mean concentration were observed only between Shiraz and Mashhad [P=0.021]; and Shiraz and Rasht [P=0.003]. By increasing age of individuals, there were also a negative correlation at mean concentrations of T4 and T3 in Ilam [P=0.022], and Mashhad [P=0.016] respectively. According to these data, and specificity of environmental and genetic factors to each popualtions, specific 'normal reference' of T4 and T3 homones should be considred for each of these populations. Correlation study of mean concentrations of these hormones and genetic variations of some critical genes such as thyroid peroxidase [TPO] and iodothyronine deiodinase can open new window of epidimiology among Iranian popualltions