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Vitamin D

What Is Vitamin D?

Vitamin D, often called the "sunshine vitamin," is an important nutrient. Its active form, called calcitriol, behaves like a hormone in the body. The body can produce 10,000 IU or more of vitamin D with as little as 10 to 15 minutes of exposure to summer sunlight.

Vitamin D plays a crucial role in supporting and maintaining bone health. There are few natural food sources that contain vitamin D. Food manufacturers began fortifying milk and other products with vitamin D decades ago, aiming to wipe out rickets, a childhood bone disease.

Receptors for this important hormone are found in virtually every type of cell and tissue in the body. Receptors work like locks: The lock turns when the right key is inserted, prompting the cell to act in a certain way. Evidence shows that people with higher levels of vitamin D may live longer.

Studies also suggest that a majority of Americans have insufficient or deficient levels of vitamin D.

Why Do You Need Vitamin D?

The presence of vitamin D receptors throughout the body hints at the importance of the vitamin. Research shows that vitamin D plays a crucial role in the health of the immune system, brain, heart, and blood vessels, among other organs and systems.

Many doctors now monitor their patient’s vitamin D levels and prescribe supplemental vitamin D when levels are too low. A lack of vitamin D may increase your risk of developing numerous diseases and conditions.

Autoimmune diseases — such as type 1 diabetes, multiple sclerosis, and rheumatoid arthritis —may be linked to a vitamin D deficiency. Autoimmune diseases occur when the immune system attacks the body’s own tissues. Too little vitamin D has been linked to poor immune system function.

Vitamin D deficiency is also linked to a risk for type 2 diabetes, osteoporosis (a condition that results in brittle bones), heart disease, mood disorders, and even certain types of cancer. This is because the active form of vitamin D helps control chronic inflammation. Ongoing inflammation has been linked to diseases such as hardening of the arteries (atherosclerosis), arthritis (painful, inflamed joints), and even cancer.

Supplementation Recommendations

Vitamin D may be taken as a supplement. Two forms are available: vitamin D-3 and vitamin D-2. Vitamin D-3 is preferable, as it is better absorbed when taken by mouth.

Current government recommended dietary intakes for vitamin D range from 400 IU to 800 IU depending on your age, but are based on the needs of healthy individuals, not someone who may already be deficient or battling an illness or disease. Many experts argue that higher daily intakes above what’s recommended, even what may be considered megadosing (up to 50,000 IU per week), are required to achieve better health outcomes.

Vitamin D Deficiency

The following factors can affect your vitamin D levels:

  • exposure to sunlight
  • the use of sunscreens
  • body mass
  • skin color
  • diet

People with dark skin don’t make vitamin D as easily as light-skinned people when exposed to sunlight.

Vitamin D dissolves in fat, and is stored in fat cells. Overweight people tend to have more vitamin D stored in fat rather than circulating in the blood. They may require higher doses of vitamin D-3 to maintain optimal serum levels.

Vitamin D Toxicity

Vitamin D toxicity, resulting from taking too much supplemental vitamin D, is relatively rare. The amount of supplemental vitamin D needed to cause vitamin D toxicity is more than 10,000 IU per day, taken every day for months. The tolerable upper intake levels published by the U.S. government range from 1,000 IU per day for infants, to 4,000 IU per day for children over 9 years old and adults. 

Content licensed from:

Written by: Dale Kiefer
Medically reviewed on: Mar 23, 2016: Natalie Butler, RD, LD

This feature is for informational purposes only and should not be used to replace the care and information received from your health care provider. Please consult a health care professional with any health concerns you may have.
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