A review of the critical role of vitamin D in the functioning of the immune system and the clinical implications of vitamin D deficiency.
Mol Nutr Food Res. 2010 Sep 7.
Schwalfenberg GK. University of Alberta, Edmonton, Alberta, Canada.
This review looks at the critical role of vitamin D in improving barrier function, production of antimicrobial peptides including cathelicidin and some defensins, and immune modulation. The function of vitamin D in the innate immune system and in the epithelial cells of the oral cavity, lung, gastrointestinal system, genito-urinary system, skin and surface of the eye is discussed. Clinical conditions are reviewed where vitamin D may play a role in the prevention of infections or where it may be used as primary or adjuvant treatment for viral, bacterial and fungal infections. Several conditions such as tuberculosis, psoriasis, eczema, Crohn's disease, chest infections, wound infections, influenza, urinary tract infections, eye infections and wound healing may benefit from adequate circulating 25(OH)D as substrate. Clinical diseases are presented in which optimization of 25(OH)D levels may benefit or cause harm according to present day knowledge. The safety of using larger doses of vitamin D in various clinical settings is discussed. PMID: 20824663
by Dr. Gerry Schwalfenberg MD, CCFP, FCFP
Blog posted at Vitamin D Society
Why do some people die from COVID-19, and others do not? As we re-open our economies, how can we manage risks and protect ourselves. We know age and some diseases place us at increased risk but these may not be modifiable. What can we modify?
I have been researching the effects of vitamin D on the human body for about 15 years, and I’m struck by how low levels of vitamin D seem to be correlated to higher risk from COVID-19.
You can get vitamin D from various sources, but the most common source is sunlight. Exposing your skin to sunlight, without burning, increases your vitamin D levels. Inevitably, certain populations and certain countries spend more time outside. You can see the impacts on vitamin D levels, and we may also be seeing those impacts on COVID-19 levels.
The COVID 19 pandemic began in the northern hemisphere during the winter months of 2019/2020. Areas which were hardest hit were large cities like Wuhan, northern Italy, and parts of Spain which have noticeably less solar radiation and more air pollution (which blocks ultraviolet frequencies required for vitamin D production in the skin). These areas also had an aging population and more smokers, and both of these populations are known to have lower vitamin D levels. Even in sunny countries like Indonesia, there are those with low levels of vitamin D who cover the skin from the hot sun. Countries in the southern hemisphere who had just came out of the summer when the pandemic hit were less likely to be impacted.
The vitamin D connection becomes even more interesting when you consider a number of other factors. COVID-19 has disproportionately affected people living in long-term care facilities, and people from ethnic minority communities. There are a lot of possible reasons for this, but one may be that people in long-term care facilities are less likely to be spending time outside, and that darker skin acts as a kind of natural sunscreen which increases the risk of vitamin D deficiency for those who spend the same amount of time in the sun.
Canadians tend to have lower levels of vitamin D at the end of winter, with more than 40% of Canadians having 25(OH)D levels less than 50nmol/l. This level is considered to be deficient by many experts on Vitamin D. Low vitamin D levels are already associated with many different kinds of health problems – so regardless of COVID-19, low vitamin D is also a pandemic that needs to be addressed. Average 25(OH)D levels in Canada at the best of times are about 62 nmol/l according to a Canadian household study, substantially below what is recommended. This pandemic of low vitamin D leaves us vulnerable to other pandemics.
So, what can we do? It’s fairly simple - people need sun exposure for their bodies to naturally produce vitamin D. The sun is an excellent source of vitamin D and it is free. One minimal erythemal dose of sun exposure during the summer months without burning and without sunscreen, arms and legs exposed to mid-day sun for 20 minutes with type 1-2 skin can produce about 5-10,000 IU of vitamin D. Those with more skin pigmentation will require more time. Vitamin D supplementation can help as well especially after the summer.
More research is certainly needed about the possible link between vitamin D deficiency and COVID-19. But regardless of that link, you cannot go wrong by increasing your vitamin D levels. Though not certain, it is possible that we could have prevented the problems of the COVID-19 pandemic if we had done more about the vitamin D deficiency pandemic. With this information, maybe we can now prepare for an expected second wave.
Gerry Schwalfenberg MD, CCFP, FCFP
Assistant Clinical Professor, Department of Family Medicine University of Alberta
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