The link between low Vitamin D levels, respiratory infections, and a weak immune system

The link between low Vitamin D levels, respiratory infections, and a weak immune system

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In this time of heightened fear around COVID-19, it is important to do all one can to minimize exposure and improve your overall immune health.  The saying “leave no stone unturned” is extremely important at times like this.  Wearing masks and gloves, washing our hands, not touching our faces and using sanitizers seem to be the main focus among the experts.  What’s being left out is the conversation is what we can do to take care of our immune system.  One of my popular sayings during times like these is sick people get sick.  While this may be offensive to some, there is truth to it.  If you have a healthy and properly functioning immune system, your body will fend off even the most ferocious infections. 

Having said this, there are many things we can do to help support the body’s fight against any type of infection viral or bacterial.  Simple things like avoiding sugar[i], get proper amounts of sleep[ii], exercise[iii], eating healthy[iv], maintaining a healthy weight[v], using dietary supplements and maintaining a healthy vitamin D level[vi] all play a role in having a healthy immune system.  Of all of these, maintaining a healthy vitamin D level may be the easiest place to start.   

Vitamin D has an impact on the two main branches of our immune system: Innate and Adaptive[vii].   Innate immunity is something you are born with and is considered the body’s first line of defense against disease.  On the other hand, adaptive immunity develops as we age.  As we get exposed to diseases, allergens, and vaccines, we develop the antibodies to fight off disease caused by bacteria, viruses, and allergens.  

There are numerous published clinical studies confirming that low blood levels of vitamin D are associated with an increased risk of infections[viii].  Below are a few compelling examples of how low blood levels of vitamin D put you at risk. 

Influenza (viral infection)

A therapeutic dose of vitamin D showed that vitamin D administration resulted in a 42% decrease in the incidence of influenza infection[ix].  

Upper respiratory infections

Individuals with lower vitamin D levels (<30 ng/ml) were more likely to self-report a recent upper respiratory tract infection than those with sufficient levels[x].

Recruits (soldiers) with lower vitamin D levels lost significantly more days from active duty due to upper respiratory infections than recruits with higher vitamin D levels (above 40nmol)[xi].

Vitamin D levels linked to seasonal daylight hours

Vitamin D levels fluctuate throughout the year primarily due to the amount of sun we are exposed to.  There appears to be an association between the number of infections and the seasons i.e. more infections in the shorter daylight times of the year[xii].  

In this time of Global concern over the COVID-19 pandemic and a flourishing flu season, knowing something as simple as your vitamin D level may mean the difference between a weak or strong immune system.  Several years ago, the non-profit organization Organic and Natural Health Association launched a campaign “Power of D” which helped educate consumers on the importance of knowing their vitamin D levels and to help gather more scientific information on the benefits of vitamin D.  Because of their hard work and efforts, you too can you know your vitamin D level.  A simple at-home finger-stick blood test is an easy way to learn whether or not you should be taking a vitamin D supplement.  Vitamin D supplements are readily available and very inexpensive to buy.  Wouldn’t it be sad if something as simple as knowing your vitamin D level and taking a D supplement daily stood between you and being able to have a healthy immune system?


[i] Ullah H, Akhtar M, Hussain F, Imran M, Effects of Sugar, Salt and Distilled Water on White Blood Cells and Platelet Journal of Tumor Cells Vol 4, No 1 (2016)

[ii] Besedovsky L, Lange T, Born J. Sleep and immune function. Pflugers Arch. 2012;463(1):121–137. doi:10.1007/s00424-011-1044-0

[iii] Campbell JP, Turner JE. Debunking the Myth of Exercise-Induced Immune Suppression: Redefining the Impact of Exercise on Immunological Health Across the Lifespan. Front Immunol. 2018;9:648. Published 2018 Apr 16. doi:10.3389/fimmu.2018.00648

[iv] Chandra R, Nutrition and the immune system: an introduction., Am J Clin Nutr. 1997 Aug;66(2):460S-463S.

[v] Nieman D, Nehlsen-Cannarella S, Henson D, et al., Immune response to obesity and moderate weight loss.

Int J Obes Relat Metab Disord. 1996 Apr;20(4):353-60.

[vi] Aranow C. Vitamin D and the immune system. J Investig Med. 2011;59(6):881–886. doi:10.2310/JIM.0b013e31821b8755


[vii] Aranow C. Vitamin D and the immune system. J Investig Med. 2011;59(6):881–886. doi:10.2310/JIM.0b013e31821b8755


[viii] Cannell JJ, Vieth R, Umhau JC, Holick MF, Grant WB, Madronich S, Garland CF, Giovannucci E, Epidemic influenza and vitamin D., Epidemiol Infect. 2006 Dec; 134(6):1129-40.

[ix] Urashima M, Segawa T, Okazaki M, Kurihara M, Wada Y, Ida H, Randomized trial of vitamin D supplementation to prevent seasonal influenza A in schoolchildren.,  Am J Clin Nutr. 2010 May; 91(5):1255-60.

[x] Ginde A, Mansbach J, Camargo C, Association between serum 25-hydroxyvitamin D level and upper respiratory tract infection in the Third National Health and Nutrition Examination Survey., Arch Intern Med. 2009 Feb 23; 169(4):384-90.

[xi] Laaksi I, Ruohola JP, Tuohimaa P, Auvinen A, Haataja R, Pihlajamäki H, Ylikomi T, An association of serum vitamin D concentrations &lt; 40 nmol/L with acute respiratory tract infection in young Finnish men.,  Am J Clin Nutr. 2007 Sep; 86(3):714-7.

[xii] Aranow C. Vitamin D and the immune system. J Investig Med. 2011;59(6):881–886. doi:10.2310/JIM.0b013e31821b8755