Vitamin D and thyroid function of pregnant women in a sunny region: is there any connection?

The aim of this study was to investigate the relationship between vitamin D serum concentrations and thyroid hormones of pregnant women living in a sunny region of Northeast Brazil.

This is a cross-sectional secondary analysis of a study that evaluated the iodine status of pregnant women attending prenatal consultations in a tertiary hospital. Consecutive patients (>18 years) were conveniently sampled. Blood samples were collected for the study, including measurements of vitamin D, anti-TPO, and anti-Tg antibodies, thyroid-stimulating hormone, total and free thyroxine (TT4, FT4), and total and free triiodothyronine (TT3, FT3). Vitamin D levels <20 ng/mL were considered deficient. Between 20 and 30 ng/mL were classified as insufficient, and >30 ng/mL were sufficient. Additional data on urinary iodine concentrations, anthropometry, sociodemographic, and gestational features were also collected.

A total of 562 pregnant women were included, with a median age of 29 years. Most of them (47.9%) were in the first gestational semesters. Only 3.9% of subjects presented with vitamin D deficiency, while 81% had insufficient values and 15.1% had sufficient levels. Vitamin D levels were not significantly correlated or associated with thyroid hormones or body mass index (all p-values >0.05).

Our study adds to the growing body of evidence highlighting the importance of assessing the status of both vitamin D and thyroid hormones in population- and region-specific contexts, as it may vary accordingly.