Vitamin D: The Wonder Vitamin
By Jennifer Koslo, MS, RD, CSSD, ACE-CPT
Full-time faculty member, Kaplan University School of Health Sciences

Vitamin D, specifically vitamin D3 (cholecalciferol), has received positive press lately and may be one of the most underrated vitamins.

Medical journals have published recent research on vitamin D and the implications it can have on personal health. But what exactly do the findings mean for your health?

To discover the answer to this question and more, pull up a chair in the sun, pour yourself a tall glass of a vitamin D-fortified beverage, and read on!

Just the facts: What is vitamin D?
Vitamin D is technically not a vitamin but a secosteroid hormone, similar in structure to a steroid, that interacts with almost 1,000 genes in the body.

The fact that vitamin D functions as a hormone and interacts with so much of our DNA makes it easy to see how it can be a factor in the pathology of heart disease; stroke; hypertension; autoimmune diseases, such as multiple sclerosis, diabetes, depression, chronic pain, osteoarthritis, and osteoporosis; birth defects; periodontal disease; and at least 17 varieties of cancer.1

There are three forms of vitamin D: cholecalciferol, calcidiol, and calcitriol. Cholecalciferol is the naturally occurring form, which is made in large quantities when your skin is exposed to the sun. It is also referred to as vitamin D3 and is the form that can be taken as a supplement.

Calcidiol is the form that exists in your blood and is made from cholecalciferol. To measure the amount of vitamin D in the body, a blood test will determine how much calcidiol is circulating in the blood. This test is known as 25-hydroxyvitamin D.

Calcitriol, made from calcidiol in the kidneys and other tissues, is the most potent form of vitamin D and has anticancer properties. Calcitriol is often referred to as the active form of vitamin D, but it should not be used to determine if you are vitamin-D deficient.

What are the current recommendations?
Vitamin D recommendations are given in micrograms (ug). For adult males and females age 19 to 50, the suggested vitamin D intake is 5 ug. For ages 51 to 70, it is 10 ug.

You may also see recommendations that use the new International Units (IU), in which 1 ug equals 40 IU. The current recommended dietary allowance (RDA) for men and women age 50 or younger is 200 IU.

How much vitamin D does my skin make?
Just 20 to 30 minutes of full skin exposure to the midday sun or to the lights in a tanning booth will result in the production of 10,000 to 50,000 units of vitamin D, which is more than enough to meet your needs.

However, there are many reasons that people don’t get 20 to 30 minutes of sun exposure. Sunscreen, clothing, and glass all block the UVB rays that make vitamin D. In addition, many people live in areas where there is a lack of sunlight due to cloud cover or colder temperatures.

Why is vitamin D crucial to health?
The most important part of vitamin D metabolism occurs after cholecalciferol is made by the skin, or taken as a supplement, and is transported to the liver and converted into calcidiol.

Calcidiol is important for maintaining calcium blood levels. For the majority of people, this regulation of calcium by way of the kidneys is what uses up the typical vitamin D intake.

However—and this is key—if you take in enough vitamin D to satisfy the first pathway of maintaining calcium blood levels and have enough left over, then the excess vitamin D takes a second pathway that leads to the tissues. It is in the tissues that all of the health benefits discovered in the last 10 years occur ...


Kaplan Higher Education Corporation is a division of Kaplan, Inc., a subsidiary of The Washington Post Company.

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