Vitamin D is not really a vitamin. It is a steriod and exists in two forms, D2 (ergocalciferol) and D3 (cholecalciferol). D3 is the more active form and is found naturally in the human body. D2 is derived from radiating fungi and is only found in very small amounts in the body. Most over-the-counter (OTC) supplements use the D2 form rather than D3. Also, there are two prescription forms of it: Drisdol and Calciferol. D3 may be purchased without a prescription.
The Vitamin D Council says "Current research has implicated vitamin D deficiency as a major factor in the pathology of at least 17 varieties of cancer as well as heart disease, stroke, hypertension, autoimmune diseases, diabetes, depression, chronic pain, osteoarthritis, osteoporosis, muscle weakness, muscle wasting, birth defects, periodontal disease, and more."
According to Dr. Hollis' article, it has been almost 4 decades since the definition of "normal" was established for Vitamin D using the first assay assessing circulating 25-hydroxyvitamin D [25(OH)D] in human subjects. These "normal" results were obtained by sampling human subjects who appeared to be free from disease, and by assessing "normal" circulating 25(OH)D levels using a Gaussian distribution of the values.
Hollis states, "...the ‘normals’ were actually vitamin D deficient." He says this is similar to defining “normal” estrogen levels by sampling a population of women who are primarily postmenopausal.
He goes on to say:
To make matters worse, the dietary requirement for vitamin D in adults is 200The article delineates the methods which have been FDA approved and compares them to the newer LC/MS methods which have not been calibrated against the standard DiaSorin methods. Dr. Hollis calls for standardization of reference ranges and testing.
IU/d, as defined by the Adequate Intake (AI) by the Food and Nutrition Board and
is essentially meaningless.
In an interview a couple of years ago, Dr. Hollis was quoted:
It is maddening to me to hear physicians say "drink some milk and you will
obtain all the vitamin D you need." It is wrong and harmful to the patient. No
one should have a circulating 25(OH) D level—this is the metabolite that defines
nutritional vitamin D status—less than 80 nmol. I try to keep my own level at
125 nmol minimum and consume between 2,000-8,000 IU/day depending on the season.
Based on this information and other research (see references at the end of the article), the
“optimum level” of Vitamin D in the human body is much higher than the ranges used now, and it has yet to be determined.
Bruce W. Hollis (2008). Assessment of vitamin D status and definition of a normal
circulating range of 25-hydroxyvitamin D Current Opinion in Endocrinology, Diabetes & Obesity, 15 (6), 489-494 DOI: 10.1097/MED.0b013e328317ca6c
To read more:
- Assay Variation Confounds the Diagnosis of Hypovitaminosis D: A Call for Standardization
- Assessment of dietary vitamin D requirements during pregnancy and lactation
- Circulating Vitamin D3 and 25-hydroxyvitamin D in Humans: An Important Tool to Define Adequate Nutritional Vitamin D Status
- Presentation by Dr. Hollis