Vitamin D Helps the Immune System During Cold and Flu Season


Vitamin D helps the immune system stay balanced, much like a gymnist walking a balance beam.

Vitamin D helps our immune systems stay balanced during the cold and flu season, and serve as a pharmacy resource.

There are Vitamin D receptors and activating enzymes on the surfaces of all White Blood Cells. The role that vitamin D plays in keeping the immune system healthy is very complex because the immune system has to be perfectly balanced. If there is too much stimulation, autoimmune diseases can set in. If there is not enough immune system activity, frequent infections can occur.

Low levels of vitamin D have been linked with both extremes, and low levels of vitamin D have been associated with worsening autoimmune diseases. Low levels of vitamin D are not the underlying cause of the autoimmune disease, but low levels of vitamin D can make autoimmune disease states worse.1

Low levels of vitamin D have also been associated with frequent infections. In 2009, the National Institute of Health warned that low vitamin D levels are associated with frequent colds and influenza.2

And so it appears that vitamin D helps keep the immune system balanced much like a gymnast walking on a balance beam.

Since the NIH announcement, there have been many studies to determine the best regimen of vitamin D supplementation and to better understand this association.

In 2017, a large analyses of prospective clinical trials showed that taking vitamin D reduces the odds of developing a respiratory infection by approximately 42% in people with low baseline levels of 25-hydroxyvitamin D; below 25 ng/mL.3

The analysis suggests that taking vitamin D daily or weekly was more effective than larger doses taken in single or monthly boluses. The most common daily dose used was vitamin D3 300-4,000 IU.

In a recent study, researchers found monthly high-dose vitamin D supplementation does not prevent acute respiratory infections in older adults with low levels of vitamin D. They performed a randomized, double-blinded, placebo-controlled trial of 5110 adults. Participants were given 200,000 IU vitamin D3 followed by 100,000 IU monthly (n=2,558) or placebo (n=2,552) for a median follow-up 1.6 years.4

Study participants reported upper and lower acute respiratory infections on monthly questionnaires. A slightly higher majority (74.1%) of vitamin D users reported at least 1 respiratory infection, whereas 73.7% of the placebo group reported at least 1 respiratory infection. The hazard ratio for vitamin D compared to placebo was 1.01 (95%CI, 0.94, 1.07).

This flu season, it is important for pharmacists to convey that daily and weekly vitamin D supplementation helps keep the immune system balanced during the cold and flu season.


  • Szodoray P, Nakken B., Gaal J, et al. The complex role of vitamin D in autoimmune diseases. Scand J Immunol. 2008 Sep;68(3):261-9. doi: 10.1111/j.1365-3083.2008.02127.x. Epub 2008 May 29. Accessed September 20, 2019.
  • National Institutes of Health. Low Vitamin D Levels Associated with Colds and Flu. NIH website. Published March 9, 2009. Accessed September 14, 2019
  • Martineau AR, Jolliffe DA, Hooper RL, et al. Vitamin D supplementation to prevent acute respiratory tract infections: systematic review and meta-analysis of individual participant data. BMJ. 2017­;356:i6583.
  • C A Camargo, JSluyter et al, Effect of monthly high-dose vitamin D supplementation on acute respiratory infections in older adults: A randomized controlled trial. Clin Infect Dis. Published August 17, 2019. Accessed September 20, 2019.

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