High leptin levels in women developing postpartum thyroiditis

BACKGROUND There is experimental evidence that leptin is required for the development of T helper 1 (Th1)-mediated autoimmune diseases. However, to our knowledge, there are no studies demonstrating such a role in human autoimmune thyroid disease. OBJECTIVE In the present study we have retrospectively examined patients developing postpartum thyroiditis (PPT), as a model of autoimmune disease, for changes in serum leptin levels during the postpartum period. MATERIALS AND METHODS The study group included 61 women in the first month postpartum who were positive for thyroid peroxidase antibodies (TPOAb+ve). Twenty TPOAb-negative (-ve), age and body mass index (BMI)-matched, postpartum women were enrolled as the control group. All subjects were evaluated for BMI, serum leptin values, thyroid function [serum free-triiodiothyronine (FT3), free-thyroxine (FT4), thyrotropin (TSH)] and autoimmunity [TPOAb levels and complement activity index (C3 index)] at 4, 12, 16, 20 and 24 weeks' postpartum. During the postpartum period, 32 of 61 TPOAb+ve women (52.4%) showed one or more episodes of thyroid dysfunction (PPTD group), whereas the remaining 29 TPOAb+ve women remained euthyroid throughout the study period (PPTE group). None of the control group developed thyroid dysfunction. RESULTS Four weeks postpartum, TPOAb+ve women showed higher serum leptin values than TPOAb-ve women, despite comparable BMI. At this time, PPTE and PPTD patients showed no significant differences in leptin levels or leptin/BMI ratio. Throughout the postpartum period, PPTD patients maintained significantly higher leptin values and leptin/BMI ratio compared to the healthy women. In PPTE women, however, a significant reduction in leptin levels and leptin/BMI ratio was seen at 12 weeks' postpartum. This decrease was transient and correlated negatively with the variation in C3 index at the same time. No significant correlation was found between serum leptin variations and FT4 or TSH levels. CONCLUSIONS This study has demonstrated that women developing postpartum thyroiditis have higher leptin values compared to the healthy women. The higher levels were maintained for 6 months postpartum. This result would suggest an involvement of leptin in the pathogenesis of postpartum thyroid disease, although further studies are needed to characterize the reciprocal effects of leptin, immune system and thyroid hormones during the course of this disease.