Vitamin D


What is it?

Vitamin D is a fat-soluble vitamin that is primarily produced by the human body when exposed to sunlight.  Vitamin D is not actually a vitamin in the traditional sense, but is more of a multi-functioning agent.  The fact that sunlight (or rather, the chemical reactions initiated by exposure to certain wave-lengths of sunlight) is the body’s primary source of vitamin D can be problematic. This is particularly apparent for those who live in extreme climates, who live far from the equator, or who have to be cautious about sun exposure. 

Very few foods contain naturally occurring vitamin D, which is why there are so many foods today (usually dairy products or processed cereals) that are “fortified” with vitamin D.  Egg yolks, sardines, and cod liver oil are the most common food sources of vitamin D, so many people elect to get their vitamin D from nutritional supplements.  The preferred form of vitamin D for supplementation is D-3.  As a fat-soluble vitamin, vitamin D supplements are best absorbed when taken with a meal that contains a small amount of fat. 



The importance of vitamin D cannot be understated.  It plays a role in many body functions, including the regulation of minerals such as calcium and magnesium, immune system function, fat metabolism, and the body’s production of hormones.  Vitamin D also has anti-inflammatory properties. 

It is estimated that the majority of Americans suffer from varying degrees of vitamin D deficiency.  Vitamin D deficiency has been linked to cancer, bone disease, asthma, Crohn’s disease, ulcerative colitis, multiple sclerosis, obesity, high cholesterol, as well as low testosterone in men and low estrogen levels in women.    

Regarding hormone production, vitamin D is a major factor in how the body uses cholesterol to produce other hormones.  Several studies have shown that high doses of vitamin D over time can improve testosterone production in men and estrogen production in women, in individuals who were previously deficient.  However, individuals with optimal vitamin D levels did not see higher levels of hormone production through additional vitamin D supplementation.


Supplement dosing

There are many factors that determine the “ideal” dosing for vitamin D supplementation, but 1,000 to 4,000 iu (or 25-100 mcg) should be enough to ensure optimal levels in most people.  According to the Institute of Medicine (IOM), 4,000 iu is the safe upper limit, so do not exceed that limit without consulting a health professional.


Products we carry with this ingredient

  • NOW Vitamin D3 softgels
  • NOW liquid Vitamin D3


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