Vitamin D Metabolism in Patients With Endocrine Disorders

Inclusion Criteria: * confirmed diagnosis (arms "Cushing's Disease", "Acromegaly", "Diabetes Mellitus Type 1", "Primary Hyperparathyroidism") * active phase of the disease (arms "Cushing's Disease", "Acromegaly") * no history of surgical and specific pharmacological treatment (arm "Primary Hyperparathyroidism") * HbA1c \<8.0% (arm "Diabetes Mellitus Type 1") * absence of the specified endocrine disorders (arm "Control group") Exclusion Criteria: * factors associated with vitamin D level * intake of the following drugs during the 3 months preceding the study: vitamin D medications; glucocorticosteroids; antiretroviral drugs; antifungal drugs; cholestyramine, orlistat; antiepileptic drugs; antidepressants (fluoxetine); diuretics (spironolactone); antimicrobial agents (macrolides, tetracyclines, isoniazid, rifampin, primaquine); chemotherapy (cyclophosphamide, tamoxifen, paclitaxel, ifosfamide, irinotecan, etoposide, vinblastine); immunosuppressants (cyclosporin A, tacrolimus, sirolimus); H2 receptor antagonists. * BMI \>35 kg/m2 * pregnancy * granulomatous disease (sarcoidosis, tuberculosis, histoplasmosis, berylliosis, coccidiomycosis) * disease with malabsorption syndrome (Crohn's disease, ulcerative colitis, celiac disease, post-bariatric surgery condition, decompensation of chronic pancreatitis) * reduced renal function (eGFR \<60 ml/min/1.73m2) * laboratory signs of liver failure (hypoalbuminemia, hypoprothrombinemia) * hypercalcemia or risk factors for hypercalcemia * serum total calcium \>3.0 mmol/L * myeloma * immobilization * thiazide diuretics intake * allergy to vitamin D drugs * total 25(ОН)D \>60 ng/ml (determined by chemiluminescent immunoanalysis)