7 Signs You May Have a Vitamin D DeficiencyBy Dr. Mercola
Vitamin D deficiency is incredibly common in the US, but many Americans mistakenly believe they aren’t at risk because they consume vitamin-D-fortified foods (such as milk).
There are very few foods that actually have therapeutic levels of vitamin D naturally and even fortified foods do not contain enough vitamin D to support your health needs.
Despite its name, vitamin D is not a regular vitamin. It's actually a steroid hormone that you are designed to obtain primarily through sun exposure, not via your diet.
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http://articles.mercola.com/sites/articles/archive/2014/05/28/vitamin-d-deficiency-signs-symptoms.aspx