Special Precautions/Comments:

Additional Information:

Vitamin D is a steroid hormone which is primarily produced in the skin following exposure to sunlight. Vitamin D itself is inactive and must be hydroxylated by the liver to form 25-vitamin D, and then again by the kidney to form the biologically active 1,25-vitamin D. Vitamin D itself is present in many different forms, the most notable are vitamin D3 (cholecalciferol) and vitamin D2 (ergocalciferol). Vitamin D2 cannot be produced by the body and is obtained through the diet.  

Total 25-hydroxyvitamin D (including 25-hydroxycholecaliferol and 25-hydroxyergocalciferol) is measured and gives an indication of the overall vitamin D status. Measurement of 25-vitamin D is preferred to 1,25-vitamin D because it is more stable and the major storage form. Levels of 25-vitamin D are approximately 1000-fold greater than 1,25-vitamin D. Measurement of 1,25-vitamin D is available in certain circumstances.  

Vitamin D is essential for calcium homeostasis and bone health. Severe deficiency in children can lead to rickets. Mild deficiency can affect the absorption of dietary calcium and is a common cause of secondary hyperparathyroidism. This can result in osteomalacia, increased bone turnover, reduced bone mass and increased risk of fractures. 

Measurement of vitamin D is only recommended by NICE in patients with musculoskeletal symptoms. Routine measurement of vitamin D is not recommended in asymptomatic patients.