Final answer:
The biologically active form of vitamin D involved in calcium absorption and bone health is 1,25-dihydroxyvitamin D or calcitriol.
Step-by-step explanation:
The biologically active form of vitamin D that is involved in calcium absorption and bone health is 1,25-dihydroxyvitamin D. When vitamin D is synthesized in the skin or ingested, it must first be converted to calcidiol in the liver, and then to calcitriol in the kidneys. Calcitriol, or 1,25-dihydroxycholecalciferol, stimulates the absorption of calcium from the digestive tract, promotes its reabsorption in the kidneys, and maintains normal serum concentrations of calcium and phosphate, which are essential for bone health. Deficiencies in vitamin D can lead to diseases such as osteoporosis, osteomalacia, and rickets. To address deficiencies, vitamin D is added to various foods and supplements to ensure adequate levels for maintaining health.