If you haven’t already heard, Vitamin D supplementation can provide a powerful boost to your health. It’s vital for immune health, blood sugar control, heart disease and osteoporosis prevention, autoimmune diseases, anti-aging, and the list goes on. As a matter of fact, vitamin D helps to regulate over 2,000 genes, which is about ten percent of the entire human genome, making its influence on the body greater than just about anything.
Most of our vitamin D is produced by the body itself when it’s exposed to ultraviolet radiation (UVB) in sunlight. However, this may be a problem in winter or when people purposely avoid the sun. For these folks, supplementation can provide the vitamin D they’re not getting naturally.
When it comes to vitamin D levels, the obvious question is just how much does the human body really need? “Normal” blood levels are currently listed as between 30 to 100 nanograms per milliliter (ng/ml), but optimal levels really begin at 60 ng/ml, especially if you’re interested in preventing cancer. The target range for optimal health is generally 60 to 90 ng/ml, or 60 to 70 ng/ml as a more conservative target.
New research reveals that most of us are getting no where near enough vitamin D to achieve these healthy levels.
Researchers at the University of California San Diego evaluated 3,667 men and women between the ages of 40 to 65 years old in regards to vitamin D supplementation. In 97.5% of those studied, they found that it took a dose of 9,600 IU of vitamin D3 to reach blood levels above 40 ng/ml. 
As people age their ability to absorb vitamin D from the sun or through supplementation diminishes. Many patients often need vitamin D3 supplementation well in excess of 10,000 IU, reaching requirements of up to 20,000 IU per day.
For optimal health, consider working with your doctor to insure that you’re taking enough vitamin D3 to bring your 25-hydroxy-vitamin-D level between 60 to 90 ng/ml. To reach this range, most people will need 10,000 IU daily or possibly more, depending on skin color, distance from the equator, and exposure to the sun’s rays. Also, if one is lean they will experience less difficulty raising vitamin D levels, while an obese person will usually require more.
What About Vitamin D Toxicity?
The UCSD study found that vitamin D becomes toxic in the body when it exceeds levels of 200 ng/ml. Upon conclusion, the authors stated that, “Universal intake of up to 40,000 IU vitamin D per day is unlikely to result in vitamin D toxicity.” 
Considering that 20,000 IU of D3 per day will provide those with very poor absorption the optimal blood levels of vitamin D, it stands to reason that the actual risk of vitamin D toxicity is basically non-existent for any healthy individual. Only those with granulomatous diseases, such as sarcoidosis, need to worry about vitamin D. In addition, some who use medications that alter differentiation of cells, such as epidermal growth factor receptor (EGFR) inhibitors, erlotinib and gefitinib should avoid vitamin D.
Vitamin D Co-Factors
Vitamin D is more effective when taken in conjunction with its co-factors, especially magnesium, vitamin A, vitamin K, and zinc.
Magnesium produces enzymes that metabolize vitamin D.  A magnesium shortage can decrease the production of vitamin D’s active form, 1,25(OH)2D (calcitriol).  Finally, magnesium helps optimize vitamin D’s influence over the immune system. 
Vitamin A (retinol/retinyl palmitate) plays a crucial role in how vitamin D works in the body.
Vitamin K prevents elevated blood calcium, which can sometimes rise in those taking a lot of vitamin D, and zinc helps vitamin D bind to its receptor. , , 
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