Cholecalciferol (Vitamin D)

Cholecalciferol (25-OH-D) in Serum

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 hypercalcemia1,5; 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


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 form7-9.

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.

Food Sources

Foods rich in vitamin D include beef liver, cheese, egg yolks and fatty fishes like tuna, mackerel, and salmon.

(1) Higdon J, Drake VJ, Delage B. (July 2017). Linus Pauling Institute. Micronutrient Information Center. Vitamin D. Retrieved from
(2) Shab-Bidat S, Bours S, Geusens PPPM, Kessels AGH, van den Bergh JPW. Serum 25(OH) response to vitamin D3 supplementation: A meta-regression analysis. Nutrition 2014; 30: 975-985
(3) Dhibar DP, Sahu KK, Bhadada SK. Vitamin D deficiency: Time for a reality check of the epidemiology. Re. “The increasing problem of subclinical and overt hypervitaminosis D in India: An institutional experience and review.” Nutrition 2018; 145-147.
(4) Sharma LK, Dutta D, Sharma N, Gadpayle AK. The increasing problem of subclinical and overt hypervitaminosis D in India: An institutional experience and review. Nutrition 2017; 34:76-81.
(5) Vitamin D Council. (n.d.). What is vitamin D? Retrieved from
(6) Razzaqe Mohammed S. Can adverse effects of excessive vitamin D supplementation occur without developing hypervitaminosis D? Journal of Steroid Biochemistry and Molecular Biology 2018; 180: 81-86.
(7) Kennel KA, Drake MT, Hurley DL. Vitamin D Deficiency in Adults: When to Test and How to Treat. Mayo Clinic Proceedings. 2010;85(8):752-758. doi:10.4065/mcp.2010.0138.
(8) Bralley, J.A., Lord, R.S. (2012). Laboratory Evaluations for Integrative and Functional Medicine. 2nd ed. Duluth, Ga: Metametrix Institute.
(9) Combs, G. F. Jr., McClung, J.P. (2017). The Vitamins: Fundamental Aspects in Nutrition and Health. 5th ed. Massachussetts: Academic Press.
(10) Holick MF, Binckley NC, Bischoff-Ferrari HA, Gordon CM, Hanley DA, Heaney RP, Murd MH, Weaver CM. Evaluation, treatment, and prevention of vitamin D deficiency: an Endocrine Society clinical practice guideline. J Clin Endocrinol Metab 2011; 96:1911-1930.
(11) Philippine Dietary Reference Intakes. 2015. Department of Science Technology-Food and Nutrition Research Institute.