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Vitamin D Facts

The Vitamin D Council argues that one of the most important vitamin D facts to remember is that blood levels between 50–80 ng/ml (125–200 nmol/L) are required to preserve our health and protect us against cancer. Approximately 5,000 IUs of vitamin D are needed daily to preserve these levels.

To view comments about vitamin D dosage and supplements visit our Vitamin D Forum.

One of the most important vitamin D facts is that it is essential for the efficient use of calcium by the body. And calcium is vital for our nervous system and bone health. If we do not have enough calcium to meet our body’s needs, our parathyroid glands will increase PTH hormone production and take calcium from our skeleton. Recent research now suggests that even modest vitamin D deficiency can increase the risk of osteoporosis and other health problems.

But another of the most important vitamin D facts is that supplements may not be for everyone. There are some diseases for which supplements may actually be harmful. To appreciate why this might be so, it is useful to understand how the body processes vitamin D.


Cholecalciferol is the form of vitamin D that is made when the sunlight strikes our bare skin and which is in vitamin D3 supplements. The body turns vitamin D3 into two very important hormones... calcidiol and calcitriol. Current studies indicate that we need about 4,000 units of cholecalciferol a day (from sunshine, vitamin D rich food or supplements) to meet the body's need for vitamin D.

CALCIDIOL (25-hydroxyvitamin D, 25(OH))

Vitamin D3 from the sun, food or supplements is transported to the liver where it is metabolized into calcidiol-also refered to as 25(OH). Calcidiol helps to maintain our blood calcium levels and is the storage form of vitamin D. It is also the form that is being tested when we have a vitamin D blood test, which is know as 25-hydroxyvitamin D in laboratories. The Vitamin D Council recommends that we maintain a vitamin D blood levels 25(OH)D between 50–80 ng/ml (125–200 nmol/L) in order to preserve our health and to protect us against cancer.Some people may be vitamin D deficient as a result of an illness rather than lack of sunshine. Diseases such as hyperparathyroidism, certain cancers (especially lymphoma), or granulomatous diseases (especially sarcoidosis) are frequently associated with low vitamin D blood levels. People with these diseases should only take vitamin D supplements under the supervision of a knowledgeable doctor in order to avoid hypercalcemia-elevated blood calcium. The following tests will held the doctor to identify an appropriate treatment program:

  • vitamin D blood tests (both 25(OH)D and 1,25(OH)2D3)
  • parathyroid hormone (PTH), and
  • sequential multi-channel analysis (SMA).

CALCITRIOL (1,25-dihydroxyvitamin D, 1,25 (OH)2D3 or 1,25D3)

Calcitriol (1,25-dihydroxyvitamin D) is made from calcidiol in our kidneys and in other tissues. It is sometimes referred to as the active form of vitamin D and is a potent steroid hormone that is believed to have powerful anti-cancer properties.When calcidiol leaves the liver, it can follow one of two pathways to create calcitriol.


The first priority for calcidiol is to go to the kidney where it makes enough calcitriol to maintain blood calcium levels. Calcium is vital to the function of our cells and without enough calcitriol in the blood, calcium levels will fall and illness will set in. The Vitamin D Council reports that at blood levels below approximately 50ng/ml (125nmol/L) all the vitamin D (calcidiol) will travel to the kidneys to maintain necessary blood calcium levels. However, diseases such as hyperparathyroidism, lymphoma and sarcoidosis disrupt the kidney’s normal regulation of calcitriol production, causing high blood calcium (hypercalcaemia).


If the kidneys are getting all the calcidiol they need to maintain blood calcium, then the remaining calcidiol is released to the tissues and cells to make tissue calcitriol. The recently discovered health benefits of vitamin D (especially those concerning cancer) are related to tissue calcitriol. Research suggests that blood levels above 50ng/ml (125nmol/L) are required to realize these benefits.



Ergocalciferol (also referred to as vitamin D2 or calciferol) is not a naturally occurring vitamin D for humans. (But it is derived from plants rather than animals and so is considered Kosher.) It was previously common within supplements but now is used primarily in fortified foods such as soy milk and orange juice. It is generally considered half as potent as vitamin D3 but is metabolized more quickly.


Doctors in the US may prescribe ergocalciferol (vitamin D2) in 50,000 units through brand name drugs such as Drisdol and Calciferol.

Other prescription medications are products of cholecalciferol (D3) metabolism. These include:

  • calcidiol (also sometimes called calcifediol with the brand names of Calderol and Dedrogyl)
  • dihydrotachysterol (brand name DHT Intensol), and
  • calcitriol (brand names are Rocaltrol and Calcijex when injected).

Vitamin D analogues (usually based on calcitriol) are frequently used in chronic renal disease when the kidney has lost the ability to make calcitriol. The best known are doxercalciferol (taken orally with a brand name of Hectorol) and paricalcitol (intravenous with the brand name Zemplar).

For vitamin D facts on supplements that prevent osteoporosis... visit Osteoporosis Treatment Guidelines.