Effects of heat stress on concentrations of thyroid hormones of workers in a foundry industry

Heat-related diseases are common disorders in many industries. Heat stress can cause changes in the secretion of some plasma hormones. The aim of this study was to determine the effects of heat stress on concentrations of serum triiodothyronine (T3) and thyroxine (T4) hormones among foundry workers. This cross sectional study was carried out with 35 workers of a foundry industry in summer 2013. In order to investigate the relationships between chronic and acute effects of heat on concentrations of thyroid hormones, 10- cc blood sample was obtained and determined using ELISA kit. Indoor air parameters were measured in mid-August at 7 workstations in this industry. Paired t- test and Wilcoxon test were applied to determine the relationships between variables before and after heat exposure. The WBGT index in the studied stations was 35°C and the mean of dry temperature and radiation was 40.53°C and 47.5± 6°C, respectively. The results of this research revealed that in the experimental group, the acute exposure to heat can cause significant decreases in the concentration of thyroid hormones and serum triiodothyronine (p< 0.001). A positive correlation was found between the concentration of T3 hormone among the workers, WBGT index, and the ambient air temperature. Acute exposure to heat can cause reduction in the levels of T3 and T4 hormones among the workers. Changes in the level of T3 hormone may be observed as one of the heat strain indexes.