Vitamin D

Why Your Body Needs It: 
Our knowledge of Vitamin D is expanding quickly.  Vitamin D regulates calcium homeostasis and therefore bone development and mineralization.  It has also been found to contribute to the immune system, both immune-enhancing and immunosuppressive effects as needed.  Additionally, it has been shown to improve antioxidant function, having an anti-cancer affect.

What Deficiency Looks Like:
Deficiency of vitamin D has been linked to osteopenia and osteoporosis.

Dietary Sources & Absorption:
Our bodies use sunlight to create vitamin D3 from our cholesterol.  The amount of vitamin D3 naturally found in food is very limited and insufficient, however many foods are fortified with vitamin D3.  Read labels to find out if your milk, dairy products, and fortified foods have vitamin D3 added to them.  Vitamin D is a fat-soluble vitamin, meaning that it must be consumed with fat in order to be absorbed. Therefore, fat-free dairy and/or fat-free salad dressing will limit the absorption of Vitamin D unless another source of fat is included with that meal, such as nuts, seeds, or avocado.  Vitamin D2 is naturally found in mushrooms that have been grown or placed in the sun.  While our bodies are not efficient at converting vitamin D2 into vitamin D3, it does contribute our levels.  Many of us require supplementation of Vitamin D3 in order to maintain our levels due to our indoor lives and sunscreen use.

What Toxicity Looks Like:
Vitamin D is stored in the body and it is possible to over supplement.  Self-supplementation over 1,000 - 2,000 IU per day is NOT recommended.  Supplementing over this amount by someone who is not deficient has been associated with anorexia, nausea, and vomiting in the short-term and hypercalcemia, leading to calcification of the kidneys, blood vessels, heart, and lung tissues in the long-term.​

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* This information is not intended to encourage self-supplementation.   As you will read in individual nutrient content, self-supplementation can be unnecessary or even dangerous.  I highly recommend micro-nutrient blood testing before choosing to take any supplements that are not whole-foods based.
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References:
Gropper SS, Smith JL, Groff JL. Advanced nutrition and human metabolism. 5th ed. Belmont, CA: Wadsworth; 2009.
Mahan L, Escott-Stump S, Raymond J. Krauses's food and the nutrition care process. 13th ed. St. Louis, Missouri: Elsevier Saunders; 2012. 
Spectracell Laboratories, Supplemental Information Reference Book