Vitamin D status including 3-epi-25(OH)D3 among adult patients with thyroid disorders during summer months

In the context of pleiotropic vitamin D effects, its role has also been investigated in thyroid pathology, in particular autoimmune thyroid diseases (AITD). However, available data concerning vitamin D status in Polish patients with thyroid disorders are inconclusive. In the study we investigated vitamin D status and adequacy of supplementation, as well as sunlight exposure during summer months among adult patients with thyroid diseases.

Adults with diagnosed or suspected thyroid disease were recruited almost entirely in an ambulatory setting between June and September in Northern Poland. Questionnaire examinations were performed, and serum concentrations of 25(OH)D₂, 25(OH)D₃, 3-epi-25(OH)D₃, and 24,25(OH)2D₃ were determined by LC-MS/MS.

Thirty men and 194 women participated in the study, mean age ± standard deviation (SD): 42 ± 15 years, mean ± SD body mass index (BMI) 26 ± 6 kg/m². Among the participants, 133 declared L-thyroxine treatment, 44 - Hashimoto's thyroiditis, 40 - nodular goitre, and 20 - hyperthyroidism and/or Graves' disease. Mean ± SD 25(OH)D level was 26.9 ± 8.2 ng/ml, and deficiency (< 20 ng/ml) was stated in 12%, insufficiency (20 ≤ 25(OH)D < 30 ng/ml) in 50.4% of study participants. Calcidiol was significantly higher in subjects who declared supplementation, mean ± SD: 29.4 ± 7.5 vs. 25.2 ± 8 ng/ml. Among participants without vitamin D supplementation sunlight exposure correlated with 25(OH)D. The C3 epimer of 25(OH)D₃ was detected in all subjects; its concentration correlated strongly with that of 25(OH)D₃. 24,25(OH)2D₃ levels also strongly correlated with those of 25(OH)D₃.

To our knowledge, the current study is the first in Poland to analyse vitamin D status in summer months among patients with thyroid diseases, as well as serum 3-epi-25(OH)D₃ and 24,25(OH)2D₃ concentrations. The data presented here indicate that vitamin D sufficiency is not attained even in summer months in patients with thyroid diseases.