The effect of lactation on thyroid activity of women

The study comprised 12 lactating (L) women, 26 women who interruped the lactating during study (IL) and 6 women failing to lactate (NL). All women gave birth to normal fullterm infants after uneventfull pregnancy and vaginal delivery. Sampling was done during the 2nd day and 10th week after parturition. Lactating women showed more pronounced decrease of thyroxine, decreased thyroxine: triiodothyronine ratio and increased TSH level during the 10th week after parturition in comparison to IL group. The women on NL group showed similar changes as L women, but without increased level of TSH in comparison to IL ones. Results suggest the effect of lactation on the thyroid activity. This effect could be due to the loss of iodine and thyroid hormones to the milk.