From the Guidelines
Calcitriol plays a crucial role in regulating calcium and phosphorus levels in the body, promoting bone mineralization, and supporting immune function, with its deficiency leading to bone disorders such as rickets or osteomalacia. The primary function of calcitriol is to increase the absorption of calcium and phosphorus from the intestines and reduce their excretion by the kidneys, which is essential for maintaining proper bone health 1. In patients with chronic kidney disease (CKD), calcitriol has been shown to lower intact parathyroid hormone (PTH) levels, improve histological features of hyperparathyroid bone disease, and increase bone mineral density when administered orally at doses of 0.25-0.5 μg/day 1. Additionally, calcitriol supports immune function by modulating the activity of immune cells, helps regulate cell growth and differentiation, and contributes to muscle function, making it a vital component of overall health 1. Key benefits of calcitriol include:
- Regulating calcium and phosphorus levels in the blood
- Promoting bone mineralization and preventing bone disorders
- Supporting immune function and muscle health
- Lowering intact PTH levels and improving bone histology in CKD patients It is essential to maintain adequate levels of calcitriol to prevent bone disorders and support overall health, and patients with CKD should be monitored closely to avoid hypercalcemia and ensure the safe use of calcitriol therapy 1.
From the FDA Drug Label
The two known sites of action of calcitriol are intestine and bone. A calcitriol receptor-binding protein appears to exist in the mucosa of human intestine. Additional evidence suggests that calcitriol may also act on the kidney and the parathyroid glands. Calcitriol is the most active known form of vitamin D3 in stimulating intestinal calcium transport Calcitriol is a synthetic vitamin D analog which is active in the regulation of the absorption of calcium from the gastrointestinal tract and its utilization in the body.
Main Functions of Calcitriol:
- Stimulates intestinal calcium transport
- Regulates the absorption of calcium from the gastrointestinal tract
- Utilization of calcium in the body
- Acts on the intestine, bone, kidney, and parathyroid glands
From the Research
Role of Calcitriol in the Body
- Calcitriol, the active metabolite of vitamin D, plays a crucial role in maintaining calcium homeostasis in the body 3.
- It stimulates intestinal calcium and phosphate absorption, thereby maintaining sufficient concentrations of these ions in the extracellular fluids, necessary for normal mineralization of bone matrix 3.
- Calcitriol exerts a number of important functions in regulating bone metabolism, including regulating the transcription of a large number of target genes 3.
Calcitriol and Bone Health
- Calcitriol is essential for maintaining normocalcemia and bone health by enhancing intestinal calcium absorption when dietary calcium intake is normal/low 4.
- When insufficient calcium is absorbed via the intestine, calcitriol levels will increase and act on mature osteoblasts and osteocytes to minimize calcium levels in bone tissue in favor of the blood calcium pool 4.
- Calcitriol treatment can be beneficial in the treatment of hereditary types of rickets and osteomalacia, such as vitamin D-dependent and vitamin D-resistant rickets 5.
Calcitriol and Vitamin D Status
- Osteomalacia results from impaired mineralization of bone that can manifest in several types, which differ from one another by the relationships of osteoid thickness both with osteoid surface and mineral apposition rate 6.
- Calcitriol, or 1,25-dihydroxyvitamin D, plays a crucial role in regulating the transfer of calcium between blood and bone, and its levels are often elevated in the initial stage of osteomalacia related to vitamin D deficiency 6.
- The goal of therapy of vitamin D-deficiency osteomalacia is to alleviate symptoms, promote fracture healing, restore bone strength, and improve quality of life while correcting biochemical abnormalities, and calcitriol may be used as part of this therapy 6.
Mechanism of Calcitriol Action
- The active form of vitamin D, 1α,25-dihydroxyvitamin D3, is a potent VDR ligand, and contributes to the maintenance of calcium homeostasis by enhancing intestinal calcium absorption, renal calcium reabsorption and bone resorption 7.
- Calcitriol also regulates bone formation, phosphorus metabolism and vitamin D metabolism, and has been shown to have actions on cellular proliferation and differentiation, immunity and inflammation, and cardiovascular function 7.