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Vitamin D

I had a surprising phone call about two weeks ago from a family that eats healthy, exercises regular and takes appropriate vitamins. At a routine health visit, the spouse came back with a Vitamin D level of 13 ng/mL, just above the threshold for Vitamin D deficiency.

Vitamin D is associated with healthy bones.

Prior to its discovery and supplementation into milk and other foods in the 1930s, weak bones and bow-legs in children were considered major public health problems. Today, Vitamin D is established as an important vitamin for calcium absorption and healthy bones, but there is also compelling evidence that Vitamin D produces additional effects, including inhibition of some cancers, effects on the cardiovascular system and protection against certain autoimmune diseases, such as multiple sclerosis. And because of these additional effects in adults, low Vitamin D remains a public health concern.  

  • VitD is formed in the skin when it is exposed to ultraviolet sunlight, the same wavelengths of sunlight that produce sunburn.
  • So when we’re exposed to the sun and worrying about burning, we’re also making Vitamin D.
  • And if we’re in a part of the country or in weather conditions when we can’t sunburn, well then we’re not making much VitD either.
  • For example, in Boston there is insufficient sunlight for VitD production during their winter months.

The good news is that Vitamin D supplements are available in two forms: ergocalciferol (Vitamin D2) and cholecalciferol (Vitamin D3).  The two forms produce equivalent responses on bone health, but VitD3 is the natural form that is produced when the skin is exposed to sunlight.

VitD2 or VitD3 does not act directly in the body. Instead, VitD must be metabolized to its active form, calcitriol.  VitD is first metabolized in the liver to 25-OH VitD.  This circulating form serves as the reservoir for further metabolism into 1,25 di-OH VitD by the kidneys; this is calcitriol, the active form of VitD.

Calcitriol binds to specific receptors in the cell nucleus of bone, intestinal tract and parathyroid gland.  Together these help control calcium absorption and bone strength.

Vitamin D

Vitamin D

One of the important points about Vitamin D supplementation for bone health is the importance of adequate calcium intake.

Since Vitamin D encourages the absorption of calcium from the intestinal tract, it is important to have an adequate amount of calcium in the diet to optimize the effects of Vitamin D on bone health.

Vitamin D is thought to be important in overall health. Receptors for calcitriol are found in many organs and in cells of the immune system. Vitamin D is also believed to control proliferation of cancer cells in the skin, breasts and prostate.

If you are wondering about whether you are taking enough vitamin D, you are not alone. There is some controversy as to the optimal blood levels of the vitamin. Talk to your prescriber or pharmacist for advice on Vitamn D supplementation or to arrange to have your blood level of Vitamin D measured. Your community pharmacist is there to help. 


NIH Office of Dietary Supplements
Vitamin D Factsheet


About Dr. Peter J. Rice

Dr. Peter J. Rice is a professor of Pharmacology emeritus at the East Tennessee State University Quillen College of Medicine and Professor of Clinical Pharmacy at the University of Colorado Skaggs School of Pharmacy and Pharmaceutical Sciences. --------------------------------------------------------------------------He received his BS in pharmacy from Northeastern University, PhD in pharmacology from the Ohio State University and PharmD from the University of Kentucky. He is a Board Certified Pharmacotherapy Specialist and practices in the ambulatory care and community pharmacy settings. Professor Rice is the author of Understanding Drug Action: An introduction to pharmacology (APhA, 2014) and is a fellow of the American Pharmacists Association. --------------------------He welcomes interesting medication questions and suggestions for future columns.