The Effect of Vitamin D Consumption During Pregnancy on Maternal Thyroid Function and Depression: A Randomized, Placebo-Controlled, Clinical Trial

background: beyond the vital function of vitamin d in the homeostasis of calcium balance, possible widespread effects of vitamin d are shown in numerous studies. objectives: the current study aimed at evaluating the effects of vitamin d supplement on thyroid function and postnatal depression. methods: in the current randomized experimental study, the vitamin d group presented with two 1000 iu vitamin d3 pills (2000 iu) daily from 26th to 28th week of gestation until birth; however, the control group received placebo. inter- and intra-group comparisons were performed in terms of maternal serum level of 25-hydroxyvitamin d, thyroid-stimulating hormone (tsh), free thyroxine (ft4), and thyroid peroxidase (tpo), and 4th week postnatal depression score. results: at birth, changes in maternal serum level of 25-hydroxyvitamin d was significantly different between the two groups (p = 0.004). the two study groups were not different significantly in terms of tsh, ft4, and tpo levels at birth (p > 0.05). while, at 4th week postnatal, depression score was significantly different between the two groups (p = 0.002). conclusions: vitamin d, 2000 iu /day in late pregnancy could induce a significant difference in the 4th week postnatal depression score independent of thyroid function.