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Well Being: Vitamin D — a second look at the science

November 18, 2021 
By Dr. Elias Markou

Have you ever asked your medical doctor to run a 25 hydroxy vitamin D blood panel? I highly recommend you do as the science on vitamin D3 and health is very convincing. Everyone should be taking vitamin D3, but there is a “however.” Before you self-prescribe vitamin D3 you should continue reading. Here is a quick lesson, vitamin D and vitamin D3 is the same, we all talk about taking vitamin D, but a quick trip to your local health food store you find out the vitamin D supplement you are looking for is called vitamin D3, the active form that your body needs. These terms are interchangeable. The vitamin D blood test you want your medical doctor to run is called the 23 hydroxy vitamin D or 25 vitamin D for short. In this article when we talk about vitamin D and vitamin D3 we are talking about the same thing.

As the pandemic slowly comes to an end, and as we look back at the last 18 months, there has been an explosion of scientific literature not seen in a while. Every topic you can imagine has had a scientific study, meta-analysis and clinical trial published. The abundance of medical and scientific research that has been published would make any researcher giddy. Vitamin D has been at the forefront of a lot of medical research that has made this vitamin the superstar of all vitamins in 2021. It is back and ready to take on the supplement aisle by storm.

In my office, testing vitamin D is the first thing I do with every patient. Over the years, I have observed that almost 90 per cent of my patients are vitamin D deficient. That is a staggering number. Research shows there is currently a worldwide vitamin D deficiency in various populations including infants, pregnant and lactating women, the elderly, individuals living far from the equator such as Canadians, persons who avoid the sun and populations with dark skin pigment. 28 studies looked at vitamin D serum levels in certain populations. Only the population of Thailand had normal vitamin D levels (Ref 1). I have measured the vitamin D in many firefighters and the data is very consistent — firefighters are deficient in vitamin D too.

The first step in managing your vitamin D is to get it tested. Have your medical professional, medical doctor or naturopathic doctor test your 25 hydroxy vitamin D or 25 vitamin D. This will require a requisition and a visit to your local blood lab clinic. Once you have your results, have your health professional determine the amount of vitamin D you should be taking. It is highly recommended that you have your doctor re-test your 25 vitamin D in four months after starting your vitamin D3 supplement. Some of you will have an easy time getting your vitamin D up. I call those patients absorbers and converters. There will be a group of you that will require a higher dose of vitamin D3 to get the results you need. The vitamin D ideal lab range is from 75 to 250 nmol/L (Ref 2). The ideal 25 vitamin D range is between 170 to 200 nmol/L. You want to get to this level and maintain this level, so it does require a few lab tests to find that sweet spot. For the many patients I’ve treated, usually they are taking 1000iu of vitamin D3. Usually it takes a few tries before we can nail the recommended vitamin D3 dose for maintenance. I have seen a few patients self-prescribe vitamin D3 and discover either their 25 vitamin D blood levels are too low or their have taken so much vitamin D3 that they have shot past the high 250nmol/L mark and now you are dealing with levels that are dangerous for their liver. Please consult a medical professional. Drug interactions with vitamin D3 include mineral oil, phenobarbitals (dilantin), digoxins and cholestyramines.  Patients with hypocalcemia and parathyroid pathology should avoid vitamin D (Ref 3).


There are many studies that have shown vitamin D can fight colds and flus, they show that the vitamin D3 manages the expression of genes that teaches your immune system to attack and neutralize a virus and bacteria. A 2017 British Medical Journal Article looked at vitamin D supplementation to see if it can prevent upper respiratory infection and the results were overwhelmingly positive. Vitamin D3 can reduce the risk of a cold or viral infection (Ref 4).
A final word for firefighters: Vitamin D found in the food supply is limited and most often inadequate to prevent deficiencies. An eight-ounce serving of dairy milk only contains 100IU of vitamin D. Supplementing your diet with vitamin D3 is likely necessary to avoid deficiency all year round (Ref 5).

  • References
    Mohr SB, Garland CF, Gorham ED, et al. Relationship between low ultraviolet B irradiance and higher breast cancer risk in 107 countries.  Breast Journal 2008;14:255-260
  • Jellin JM et al. Natural Medicines Comprehensive Database 3rd Edition. Stockton California: Therapeutic Research Faculty 2000. 1070-1074.
  • BMJ 2017; 356 doi: (Published 15 February 2017)Cite this as: BMJ 2017;356:i6583
  • Murray M. ND, Pizzorno J. ND.  Vitamin D. The Encyclopedia of Natural Medicine 1st Edition. Prima Publishing 1996: 39-43.

Dr. Elias Markou is one very busy naturopathic doctor. He is in private practice in Mississauga, Ont., and is the chief medical officer for the Halton Hills Fire Department. Dr. Markou was a firefighter for six years; he has a special interest in firefighter health,  is a writer and blogger who is regularly featured on television and radio and in print. Contact him at 

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