What is Vitamin D?
Vitamin D is not truly a vitamin.
Compounds are called vitamins only if they cannot be synthesized , and must be obtained from the diet. Vitamin D, however, is produced in sufficient quantity in the presence of sunlight and cholesterol and should not be considered a vitamin.
In addition, cholesterol is the precursor for most hormones, and Vitamin D should really be viewed as a light dependent fat-soluble hormone.
Historically we have thought that Vitamin D was involved in the absorption of Calcium and Phosphorous from the intestine, and were concerned primarily about its involvement as an osteoporosis risk factor. However, the reality is that Vitamin D is involved in a variety of metabolism functions, not just bone health.
Why is my Vitamin D level low?
There are a variety of reasons why Vitamin D levels are found to be low in an otherwise healthy person:
Inadequate Vitamin D intake, which could be a function of poor diet or a diet contaminated with other fat-soluble agents, such as organochlorine pesticides, which prevent adequate absorption.
Inadequate sunlight exposure, due in part to industrialization and conversion to an indoor lifestyle and also to medical recommendation to reduce sunlight exposure and in fact even use sunlight blocking agents. Sunscreen blocks sunlight and an SPF (sun protection factor) of 8 blocks 95% of the sun, so there needs to be a careful balance between over- and under- sun exposure.
Drinking milk is not a good source of Vitamin D, as an 8 oz glass of fortified milk contains merely 100 IU in comparison to 15 minutes of sun exposure which generates 20,000 IU of Vitamin D.
How do I replace my Vitamin D?
We typically replace Vitamin D only if the measured levels are found to be low; and this is usually associated with other endocrine abnormalities which can be addressed simultaneously. Vitamin D replacement therapy is done by oral supplement, typically using a once a week preparation. Retesting of the level should be done after three to six months of consistent replacement. Replacing Vitamin D should only be done after a blood test confirms that the levels are low, because too much Vitamin D can also cause serious complications.
Where to buy Vitamin D?
Vitamin D3 is typically prescribed, but is also available over the counter. I typically recommend purchasing it inexpensively through Amazon, since a two year supply of Vitamin D3 (50,000 units) taken once a week is cheaper than copay for a one month supply from the traditional pharmacy.