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  • Writer's pictureTimothy P. Smith MS, RD, LDN

The ABCs of Vitamin D & Covid-19: Part One

Vitamin D (also known as "calciferol") is one of the most important single micronutrients for human nutrition & metabolism; potentially the most important. It is a strange nutrient, as it can be considered a steroid, a pro-hormone, as well as a fat-soluble vitamin, simultaneously.

Molecular structure of cholecalciferol, better known as vitamin D3.


Vitamin D plays a pivotal role in a vast number of bodily systems, including:

-Overall metabolism & energy production

-Gut health

-Glucose metabolism

-Growth & development

-Gene expression

-Hormonal modulation

-Bone integrity

-Immune function

-Prevention of muscle cramps

-Anti-inflammatory processes

As a dietitian, if I had to pick one micronutrient that was the most important for overall health & wellness, it would be vitamin D.


Unfortunately, contrary to popular belief, vitamin D is not common in many naturally occurring foods. Especially those foods found in the average Westerner's diet. We can see a list of food sources below, in which we might find measurable quantities of vitamin D.

Source: U.S. Department of Agriculture, Agricultural Research Service. FoodData Central.

As we can see, most food-sourced vitamin D would have to come from cod liver oil, trout, or sockeye salmon. Any other food source below salmon would have to be consumed in impractically large quantities to fulfill most peoples' requirements.

Fortunately, we've learned enough about nutritional biochemistry to know that taking a tablespoon of cod liver "to the dome" is no longer a requirement for adequate vitamin D.


So, where can we get vitamin D then?

Most vitamin D can be garnered from the sun; vitamin D is synthesized in our skin as a consequence of UV light exposure (~15-20 minutes in direct sunlight, with some of arms & legs exposed is enough to fulfill most Americans' needs.)

Or if you live in an environment where sunlight is hard to come by, I recommend a vitamin D3 supplement (Try to find one that is USP-certified; it will say so on the label.)

Supplementation with vitamin D3 is recommended between the months of October thru May, especially for those who live north of the 37th parallel. (1,000-2,000 IU is appropriate for most individuals, with the tolerable upper intake limit (UL) being 4,000 IU/day for most Americans.)

Credit: Wickham, Rita. (2012). Cholecalciferol and Cancer: Is It a Big D3-eal?. Journal of the advanced practitioner in oncology. 3. 249-57. 10.6004/jadpro.2012.3.4.6. 


In part two, we will discuss vitamin D's role in preventing Covid-19.

Until next time,


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