25 Dihydroxy Vitamin D
Produced by: Skin
Definition / Purpose: Is responsible for increasing intestinal absorption of calcium, iron, magnesium, phosphate and zinc.
Lab Reference Range: 30 – 100 nmol/liter
When to order:

• Screening test that should be ordered when looking for thyroid disease. Why? Low Vitamin D levels are associated with hypothyroidism and autoimmune diseases of the thyroid.
• Follow up lab testing to confirm normal levels.

Pearls:
Half-life: 15 days.
Always test Vitamin D levels if you have Hashimoto’s or Graves’ Disease.
Very few foods contain Vitamin D.
It is not strictly a vitamin and may be considered a hormone.