DOI: 10.11118/978-80-7701-100-6-0114

VYHODNOCENÍ PRODUKCE 24,25-DIHYDROXYVITAMINU D3 SE ZVYŠUJÍCÍMI SE DÁVKAMI SUPLEMENTACE VITAMINEM D U ZDRAVÝCH MLADÝCH DOSPĚLÝCH

EVALUATION OF 24,25-DIHYDROXYVITAMIN D3 PRODUCTION WITH INCREASING DOSES OF VITAMIN D SUPPLEMENTATION IN HEALTHY YOUNG ADULTS

Michal Jirásko^1,2, Eliška Fousková¹, Radek Kučera^1,2, Hedvika Hatáková^1,2

¹ Ústav farmakologie a toxikologie, Univerzita Karlova, Lékařská fakulta v Plzni, Alej Svobody 76, 323 00 Plzeň, Česká republika

² Oddělení imunochemické diagnostiky, Fakultní nemocnice Plzeň, Edvarda Beneše 1128/13, 305 99 Plzeň, Česká republika

Increasing interest in vitamin D supplementation has raised concerns regarding optimal dosing and the potential risk of toxicity; however, recent evidence suggests that vitamin D toxicity may be overestimated due to the presence of additional metabolic inactivation pathways. One such pathway involves 25-hydroxyvitamin D₃ 24-hydroxylase, which converts 25-hydroxyvitamin D₃ (25OHD₃) to its inactive metabolite, 24,25-dihydroxyvitamin D₃ [24,25(OH)₂D₃]. In this study, we examined the relationship between vitamin D supplementation and serum 24,25(OH)₂D₃ levels in 38 healthy young adults (mean age 22 years) over a two-year period during winter months. Participants received increasing doses of oil-based vitamin D supplementation ranging from 1,000 to 8,000 IU per day. Serum concentrations of 25OHD₃ and 24,25(OH)₂D₃ were quantified using liquid chromatography–mass spectrometry, and body composition parameters, including body mass index (BMI), body fat percentage, fat mass, and skeletal muscle mass, were assessed using the InBody S10 system. A strong positive correlation was observed between serum 25OHD₃ and 24,25(OH)₂D₃ concentrations. The production of 24,25(OH)₂D₃ was most pronounced at moderate supplementation doses and remained stable even at the highest dose of 8,000 IU. The 25OHD₃/24,25(OH)₂D₃ ratio was higher in males and showed a significant association with BMI. Overall, vitamin D metabolic inactivation persisted across all supplementation doses, with a relatively stable metabolite ratio, suggesting that daily supplementation up to 8,000 IU during winter months does not exceed metabolic capacity and appears safe in healthy young adults for preventing seasonal vitamin D deficiency.

Keywords: vitamin D, 25-hydroxyvitamin D, 24,25-dihydroxyvitamin D, toxicity

pages: 114-118, online: 2026