Vitamin D

Vitamin D is a group of fat-soluble secosteroids, of which vitamin D3 and D2 are the most important. Vitamin D3 (cholecalciferol) is generated from exposure of the skin to sunlight, and from ingestion of fish, milk, plants. Vitamin D2 (ergocalciferol) comes from eating plants, fungi, and yeasts.

Both vitamin D2 and D3 are converted to a prehormone form in the liver called 25-hydroxyvitamin D3 first. This is then converted to the active form 1,25-dihydroxycholecalciferol (calcitriol) in the kidney.

• Increases intestinal absorption of calcium and phosphate
• Increases bone mineralization at low levels
• Increases bone resorption at high levels

Vitamin D deficiency is called by malabsorption, inadequate sun exposure, poor diet, chronic kidney disease (CKD), and/or advanced liver disease.

Vitamin D deficiency can result in:

• Rickets in children (deformities such as genu varum “bowlegs”)
• Osteomalacia in adults (bone pain and muscle weakness)
• Hypocalcemic tetany

Excessive vitamin D intake can potentially be toxic and result in hypercalcemia, hypercalciuria, decreased appetite, and/or level of consciousness change.