What Is Vitamin D? - Sources, Benefits & Symptoms of Deficiency

Instructor: Jayne Yenko

Jayne has taught health/nutrition and education at the college level and has a master's degree in education.

Vitamin D, otherwise known as the Sunshine Vitamin, is unique among vitamins because our bodies can supply us with plenty, depending on the amount of sunlight to which we are exposed. Explore the role of vitamin D in our health.

The Basics

Vitamin D is a fat-soluble vitamin, which means it can be stored in the human body. It is involved in the regulation of calcium and phosphorous, and in the maintenance of bone structure. Vitamin D also has roles in muscle and nerve development and the immune system. Although vitamin D is a vitamin, it is not considered essential because our bodies can make it.

Vitamin D was the 4th vitamin to be named, by Elmer McCollum in 1922. In 1925, Harry Steenbock developed a method of irradiating food with ultraviolet light, which increased the amount of vitamin D in food, particularly in milk. By the time his patent expired in 1945, rickets in the United States was basically eliminated. Rickets is a disorder primarily caused by deficiencies in calcium, phosphate. and vitamin D. We are now seeing a new surge in rickets, partly due to the amount of time people currently spend indoors.

Harry Steenbock and his irraditation system
Harry Steenbock and his irraditation system


Vitamin D is found in small amounts in a few food sources, such as fatty fish like herring, sardines, and tuna. Most of the vitamin D -- roughly 80 to 90 percent -- comes from sunlight. When our skin is exposed to sunlight, the cholesterol in our skin manufactures vitamin D. It can also be manufactured in laboratories. It has been added to milk since the 1930s as a way to reduce the incidence of rickets. Adults aged 19 to 70 years need 600 IU (international units) of vitamin D.


The major benefit of Vitamin D is that it helps the body absorb calcium and so is essential for strong bones. Much research is currently being done to determine the role of vitamin D in various diseases such as diabetes, cancer, and cardiovascular disease.


Those who are most at risk for vitamin D deficiency are:

  • breast-fed infants (breast milk is not a good source of vitamin D)
  • older adults (the ability of our skin to make vitamin D declines with age)
  • persons with dark skin (darker skin requires longer exposure time to sunlight)
  • persons with malabsorption issues (malabsorption issues prevent vitamin D from being absorbed into the body)
  • the obese (obesity binds vitamin D to the extra fat in the body)

Symptoms of vitamin D deficiency are soft bones, which results in rickets in children and osteomalacia (bone pain and muscle weakness) in adults. Rickets was once rampant in the U.S.

Bone with rickets compared with normal bone
Bone with rickets compared with normal bone

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