Sexual Functioning and Depressive Symptoms in Levothyroxine-Treated Women with Postpartum Thyroiditis and Different Vitamin D Status

<i>Background/Objectives</i>: Hypothyroidism and thyroid autoimmunity have a negative effect on women's sexual health, which is only partially reversed by thyroid hormone substitution. Sexual functioning in thyroid disorders after delivery has been poorly researched. The aim of our study was to compare the effect of levothyroxine on sexual response and depressive symptoms in women with postpartum thyroiditis (PPT) and different vitamin D status. <i>Methods</i>: The study population consisted of three matched groups of women with the hypothyroid phase of PPT: two groups with subclinical and one with overt thyroid hypofunction. Each group included similar numbers of women with normal and low vitamin D status. For the following six months, one group of women with subclinical hypothyroidism and all women with overt thyroid hypofunction received levothyroxine. At the beginning and at the end of the study, all participants completed questionnaires evaluating female sexual function (FSFI) and depressive symptoms (BMI-II). The remaining outcomes of interest included thyroid antibody titers, and the serum levels of 25-hydroxyvitamin D, TSH, free thyroid hormones, sex hormones, and prolactin. <i>Results</i>: Before levothyroxine substitution, women with overt and subclinical disease differed in the total FSFI score, all domain scores, and the overall BDI-II score. Within each study group, domain scores for desire were greater in women with vitamin D sufficiency than in those with vitamin D deficiency/insufficiency. Testosterone and estradiol levels were lower in women with overt than in women with subclinical hypothyroidism, while the opposite relationship was found for prolactin. Levothyroxine treatment improved all domains of female sexual function and reduced the total BDI-II score in both patients with overt and subclinical hypothyroidism and normal vitamin D status. In women with vitamin D deficiency/insufficiency, the impact of this agent was limited to arousal, lubrication, and sexual satisfaction. Levothyroxine replacement reduced thyroid antibody titers only in women with normal vitamin D status. The impact on testosterone was limited to women with normal vitamin D status, and was more pronounced in women with overt than subclinical disease. The effect on estradiol and prolactin, observed only in overt disease, was unrelated to vitamin D status. The increase in sexual functioning correlated with the following: 25-hydroxyvitamin D levels (in vitamin D-deficient/insufficient women); the impact on thyroid peroxidase antibodies, free triiodothyronine and testosterone (for desire and arousal); and the changes in the overall BDI-II score. Five years later, the quality of life was better in vitamin D-sufficient women receiving levothyroxine in the postpartum period. <i>Conclusions</i>: Low vitamin D status attenuates the impact of levothyroxine on female sexual function and depressive symptoms in women with the hypothyroid phase of PPT.