25-OH Vitamin D3

Vitamin D is a group of biologically active substances essential for calcium metabolism, immune function, and overall health.

• Cholecalciferol (Vitamin D3) – synthesized in the skin upon exposure to ultraviolet (UV) rays and obtained from food sources.
• Ergocalciferol (Vitamin D2) – acquired only through dietary intake.

To assess Vitamin D levels in the body, 25-OH Vitamin D is measured in blood, as it is the primary circulating metabolite.

Metabolism of Vitamin D

1. Liver: Vitamin D undergoes hydroxylation to form 25(OH)D, a moderately active form that binds to transport proteins and is stored in fat tissue.
2. Kidneys: 25(OH)D undergoes further hydroxylation to convert into 1,25(OH)₂D (calcitriol), the most active form of Vitamin D.

Functions of Vitamin D

• Regulates calcium and phosphorus metabolism
• Promotes bone and teeth health
• Supports the immune system
• Reduces the risk of chronic diseases (e.g., cancer, diabetes, multiple sclerosis, cardiovascular diseases, tuberculosis)

Factors Influencing Vitamin D Levels

• Age
• Season
• Dietary intake
• Ethnicity
• Geographical location and sun exposure

Deficiency & Excess

• Vitamin D deficiency can lead to rickets in children and osteomalacia in adults.
• Vitamin D toxicity may cause hypercalcemia, hyperphosphatemia, soft tissue calcification, nausea, vomiting, irritability, anorexia, and impaired physical development.