Vitamin D Deficiency


Vitamin D is a fat-soluble vitamin that plays an important role in many places throughout the body, including the development and calcification of bones. Vitamin D has several important functions in the body:

  • It helps to absorb dietary calcium & phosphorus from the intestines.
  • It suppresses the release of parathyroid hormone, a hormone that causes bone resorption.
  • It is likely involved in a wide variety of other functions


The main reasons for low levels of vitamin D are:

  • Lack of vitamin D in the diet, often in conjunction with inadequate sun exposure
  • Inability to absorb vitamin D from the intestines
  • Inability to process vitamin D due to kidney or liver disease

In addition, reduced amounts of vitamin D are made in the skin and stored in the body as we age. This is especially true in the winter months where the skin virtually ceases to produce vitamin D between October and April. In the summer months, the use of sunscreen blocks vitamin D synthesis.

Certain diseases affect the body’s ability to absorb adequate amounts of vitamin D through the intestinal tract. Examples of these include celiac disease, Crohn’s disease, and cystic fibrosis.

The liver and kidney have important enzymes that change vitamin D from the sun or food to the biologically active form of vitamin D.  People with chronic kidney and liver disease are at increased risk of low vitamin D because they lack these enzymes.


The most serious complications of vitamin D deficiency are low blood calcium (hypocalcemia), low blood phosphate, rickets (softening of the bones during childhood), and osteomalacia (softening of the bones in adults). However, these complications have become less common over time because many foods and drinks have added vitamin D.

Vitamin D insufficiency is more common, and is defined as a lower than normal vitamin D level that has no visible signs or symptoms. However, vitamin D insufficiency is associated with reduced bone density (osteopenia or osteoporosis), a mild decrease of the blood calcium level, an increased risk of falls, and possibly fractures, all of which can seriously affect a person’s quality of life. Thus, identifying and treating vitamin D insufficiency or deficiency is important to maintain bone strength. Treatment may even improve the health of other body systems, such as the immune, muscular, and cardiovascular systems, although more research is needed in these areas.