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NMU 161 – Vitamin D and Respiratory Tract Infections: In Some Cases, Less is More

Nutrition / Natural Medicine Update No 161 (April 30, 2020)

with Dr. James Meschino


Topic: Vitamin D and Respiratory Tract Infections: In Some Cases, Less is More

Source: PLOS journal June 2013


An important review article on vitamin D and respiratory tract infections was published several years back. The study reviewed data from the 11 available placebo-controlled studies looking at the effects of vitamin D on the risk of respiratory tract infections in humans, which together included 5,660 patients. Several important conclusions were drawn from the review of these studies:

The first is that individuals with sub-optimal vitamin D blood levels (below 75 nmol/L or 30 ng/ml) are at higher risk for developing respiratory tract infections. However, the same is true for individuals with vitamin D blood levels above 140 nmol/L (56 ng/ml). This makes sense as vitamin D is required for immune cells that line the respiratory tract to synthesize important molecules that pierce a hole through viruses, bacteria, and the like, destroying them on the spot before they can start an infection. At the same time, too much vitamin D can to some degree impair the release of certain cytokines that the adaptive immune system relies on to fight infections should they occur. This is why high doses of vitamin D have shown some success in helping to manage autoimmune diseases like Multiple Sclerosis  – vitamin D tones down the overzealous behavior of T and B- lymphocytes that are known to exacerbate the inflammatory and demyelinating aspects of this disease, helping to put patients into remission or keep them in remission.

Most people in our society have a blood level of vitamin D below 75 nmol/L (30 ng/ml), and they would likely derive an important immune-enhancing benefit by supplementing with vitamin D to get their vitamin D level above 75 nmol/L – a level associated with decreased risk of respiratory tract infections. On the other hand, taking mega-doses of vitamin D (5,000 – 20,000 IU per day) may elevate vitamin D blood levels above 140 nmol/L, which is shown to increase the risk of respiratory infections, including tuberculosis in some countries. It is also noteworthy that taking vitamin D supplements on a daily basis (such as 1,000 – 3,000 IU as an example) is much more effective way to enhance immune function than taking a large vitamin D dose weekly, monthly, or every 3-months (such as 10,000, 50,000 IU, or 100,000 IU). This is because a high dose of vitamin D entering the body at one time actually suppresses and weakens the immune system.

This may be a good strategy in certain autoimmune conditions, but it’s not a good strategy to help prevent respiratory tract infections across the population. So, I have suggested for a long time that everyone should know their blood level of vitamin D. If it’s below 75 nmol/L (30 ng/ml) then speak to your doctor about an effective daily vitamin D supplement dosage that can get you above this value. If your vitamin D blood level is already above 140 nmol/L (56 ng/ml) then you may be taking vitamin D supplement doses that are too high, unless your specialist has intended for this to be the case as an adjunctive measure in the management of an existing autoimmune condition.

I have included the reference for this information in the text below.


Bergman P, Lindh A, Bjorkhem-Bergman, Lindh J. Vitamin D and respiratory tract infections: A systemic review and meta-analysis of randomized controlled studies. PLOS (peer-reviewed, open-access journal). 2013; 8(6):e65835


Eat Smart, Live Well, Look Great,

Dr. Meschino

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