Clinical Information

Vitamin D is a fat-soluble vitamin that is synthesized in the skin upon exposure to sun. The metabolically active form of vitamin D is 1,25-dihydroxyvitamin D.

Vitamin D is important for bone health, muscle strength, and the immune system². It is critical for calcium and phosphate metabolism, bone and teeth mineralization, and treatment of rickets or osteomalacia³.

Signs and Symptoms of Deficiency or Toxicity

Vitamin D deficiency results from lack of exposure to sunlight, lack of routine supplementation⁴.

Typical signs and symptoms of vitamin D deficiency include tiredness, general aches, and pain in the bones⁴.

The signs and symptoms of vitamin D toxicity include hypercalcemia^1,5; low intact parathyroid hormone (iPTH)⁴; hypercalciuria, hyperphosphatemia; vomiting, loss of appetite, weight loss, thirst, excessive water intake with polyuria, constipation⁶.

Biomarker and Methods of Analysis

CHOLECALCIFEROL (25-OH-D) IN SERUM

The ideal marker for Vitamin D is the concentration of 25(OH)D3 in serum or plasma. 25(OH)D3 is the most prominent circulating form of vitamin D in the body and is the direct precursor of the active form^7-9.

Supplementation Guide

An acceptable dosage to prevent and treat and Vitamin D deficiency according to the Endocrine Society clinical practice guideline¹⁰ are as follows:

• For infants, 0-1 yr who are vitamin D deficient: 2000 IU/day of vitamin D2 or vitamin D3, or with 50,000 IU of vitamin D2 or vitamin D3 once weekly for 6 weeks to achieve a blood level of 25(OH)D above 30 ng/ml, followed by maintenance therapy of 400-1000 IU/day.
• For children, 1-18 y.o. who are vitamin D deficient, 2000 IU/day of vitamin D2 or D3 is the suggested treatment for at least 6 weeks or with 50,000 IU of vitamin D2 once a week for at least 6 weeks; followed by maintenance therapy of 600-1000 IU/day.
• For vitamin D deficient adults, the recommended dosage is 50,000 IU/dy of vitamin D2 or D3 once a week for 8 weeks or its equivalent of 6000 IU of vitamin D2 or d3 daily; followed by maintenance dosage of 1500-2000 IU/day.

Following are the upper limits for vitamin D intakes¹¹

• Infants (0-11 months): 25 mcg/day
• Children (1 y.o. and above) and adults (19 y.o. and above): 50 mcg

Certain medications interfere with the intestinal absorption of vitamin D. These include but are not limited to cholestyramine, colestipol, orlistat, and mineral oils. On the other hand, phenytoin, fosphenytoin, phenobarbital, carbamazepine, and rifampin increase vitamin D metabolism¹.