Relationship between thyroid-stimulating hormone levels and the severity of vitamin D deficiency by age group

Researchers have long been captivated by the complex molecular interactions between vitamin D and the thyroid gland. Hypothyroidism affects 2% to 4% of women of reproductive age and can impact fertility through anovulatory cycles, luteal phase defects, hyperprolactinemia, and sex hormone imbalances. This study investigated the relationship between thyroid disease and the severity of vitamin D deficiency across different age groups.

A retrospective study was conducted of 286 patient samples from individuals aged 18 to 60 years who were processed in the clinical biochemistry laboratory of our hospital. Samples were tested for thyroid-stimulating hormone (TSH) and vitamin D (specifically, vitamin D3) levels. The study samples were categorized into four clinically relevant groups based on TSH levels and into three groups based on serum 25-hydroxyvitamin D (25(OH)D) levels.

Most of the samples were from female patients (n=269), and the most common age group was 18 to 35 years (n=191, 66.78%). Subclinical hypothyroidism was identified in 120 patients, while vitamin D deficiency was present in 237 (82.87%) participants. A significant association was observed between vitamin D deficiency and the presence of thyroid disorders. Additionally, a significant negative correlation was found between TSH and vitamin D levels. Polycystic ovary syndrome was noted in 103 female patients (36.01%).

TSH and 25(OH)D levels should be screened in all women of reproductive age, not just those in high-risk groups, as subclinical and occult hypothyroidism may otherwise go undiagnosed. Furthermore, TSH should be considered the primary screening test.