Characterization of vitamin D metabolism in active acromegaly in the setting of bolus (150,000 IU) cholecalciferol treatment

Purpose To reveal distinctive features of vitamin D metabolism in patients with active acromegaly compared to healthy individuals, particularly in the setting of cholecalciferol treatment. Methods The study group included 34 adults with active acromegaly, and the control group included 30 apparently healthy adults with similar age, sex, and BMI. All participants received a single dose (150,000 IU) of cholecalciferol aqueous solution orally. Laboratory assessments including serum vitamin D metabolites (25(OH)D 3 , 25(OH)D 2 , 1,25(OH) 2 D 3 , 3-epi-25(OH)D 3 and 24,25(OH) 2 D 3 ), free 25(OH)D, vitamin D-binding protein (DBP) and parathyroid hormone (PTH) as well as serum and urine biochemical parameters were performed before the intake and on Days 1, 3, and 7 after the administration. All data were analyzed with nonparametric statistics. Results Patients with acromegaly had tendency to lower baseline 25(OH)D 3 levels ( p = 0.05) and lower 25(OH)D 3 levels ( p < 0.05) during the follow-up. They were also characterized by PTH suppression (lower baseline PTH levels and lower prevalence of secondary hyperparathyroidism), altered production of main vitamin D metabolites (higher 1,25(OH) 2 D 3 and lower 24,25(OH) 2 D 3 levels with corresponding lower 25(ОН)D 3 /1,25(ОН) 2 D 3 and higher 25(ОН)D 3 /24,25(ОН) 2 D 3 ratios) as well as concordant biochemical features (higher levels of serum phosphorus and albumin-adjusted calcium levels) throughout the study ( p < 0.05). The acromegaly group showed an increase in DBP levels after cholecalciferol intake as opposed to the control group ( p < 0.05) and had lower increase in free 25(OH)D levels ( p < 0.05). Δ25(OH)D 3 was similar between the groups ( p > 0.05), showed a negative correlation with the disease activity markers—both IGF-1 levels ( r = −0.44, p < 0.05) and fasting GH levels ( r = −0.56, p < 0.05)—and lacked correlation with BMI in the acromegaly group ( p > 0.05). Conclusion Patients with active acromegaly have dysregulated vitamin D metabolism characterized by higher 1,25(ОН) 2 D 3 , lower 24,25(ОН) 2 D 3 and altered DBP production. The response to vitamin D supplementation in acromegaly patients might be influenced by hormonal excess. Obtained results require reproducibility check and further study to develop specific clinical recommendations. Trial registration NCT04844164 (release date: April 9, 2021; retrospectively registered).