Endocrine Abstracts

Introduction: Vitamin D is a hormone that acts through the Vitamin D receptor (VDR) not only on the skeletal system but on a great number of target tissues, including thyroid gland. In recent years the association of vitamin D with autoimmune thyroid diseases (AITD), has been suggested.

VDR gene polymorphisms had been associated with an increased risk of AITD. In addition a recent meta-analysis showed that AITD patients had lower level of 25-hydroxyvitamin D. However some studies have not confirmed the association between vitamin D levels and AITD. Furthermore, data on the effects of vitamin D in thyroid hormones and TSH serum levels are very poor.

The aim of our study was to evaluate the association of vitamin D levels with thyroid function and positivity for thyroid antibodies.

Material and methods: PORMETS is a nationwide, cross-sectional study in Portugal comprising a sample of 4095 adults. Five hundred participants were randomly selected to be included in the present study. A fasting venous sample was collected and serum calcium, PTH, 25-hydroxyvitamin D [25(OH)D], TSH, FT₄, FT₃ and thyroid antibodies were measured.

Results: Our study included 286 women and 214 men with a mean age of 53.4 years.

Free thyroxine (FT₄), free triiodothyronine (FT₃), TSH and thyroid antibody levels did not present any significant linear correlation with 25(OH)D levels.

After adjustment for sex and age, TSH, FT₄ and FT₃ levels did not present any significant association with 25(OH)D levels or with low vitamin D status.

Logistic regression analysis did not show any significant association of low vitamin D status with thyroid antibodies positivity, even after adjustment for several possible confounding variables.

Conclusion: Our results do not confirm the association of vitamin D levels with thyroid function and positivity for thyroid antibodies.