There are different forms of vitamin D, both in foods and supplements. By far the most absorbable and bio-available form for you is vitamin D3. This is the form that your skin makes, when you are in the sunlight. Vitamin D2 is another popular form of vitamin D, but it cannot be absorbed or used properly by your body.
D2 vs. D3
Vitamin D2 is common in many supplements. It is of plant origin, and therefore minimally usable by humans. More often than not the vitamin D2 found in store-bought, nutritional supplements is also synthetic -- manufactured in a lab -- and is sometimes the source of the vitamin that is in vitamin D-fortified foods. Vitamin D3 is the form of vitamin D that your body chooses to make and use for its needs. It is highly active and it is the precursor of many hormones and biologically important molecules. Experts from The Linus Pauling Institute report that more than 50 human genes have special receptors for vitamin D3, and respond in a positive way to its presence.
Vitamin D3 and Sunlight
The human body was designed for spending time outdoors in the sun. This is proven by vitamin D3 synthesis. Given enough exposure to the sun's ultraviolet-B rays, your body will produce more than enough vitamin D3 to cover your needs. In this case, supplementation is not necessary.
Recommended Doses
Doctors monitor the levels of vitamin D3 in your blood in order to assess your overall vitamin D levels. Dr. Mark Hyman reports that if blood tests show you are deficient, taking 5,000 to 10,000 IU of vitamin D3 a day for three months is indicated. Your physician can determine whether you need to take such large, therapeutic doses and will monitor regularly your vitamin D3 levels in your blood until your storage is full. The maintenance dose for healthy adults is 2,000 IU.
Considerations
Dietary fat must be present for the body to absorb vitamin D. Therefore an extremely fat-restricted diet should not be undertaken while supplementing with vitamin D3.
There are several factors that can affect the amount of vitamin D a person should take. Deficiency is certainly the first, but age, weight, darkness of skin and exposure to sunlight can also play an important role.
There are other nutrient levels that should be monitored if the reason for the supplementation is osteoporosis. Vitamin K, calcium and magnesium all play an important role in bone density.
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