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Vitamin D and Immune Health

by Lewis Chang, PhD

Low levels of vitamin D in the blood (25-hydroxyvitamin D) are associated with higher risks of acute upper and lower respiratory tract infections such as flu, according to a systematic review based on 39 human epidemiological studies.1

During late winter and early spring, solar radiation is weak and the vitamin D synthesis via our skin is at its lowest. As a result, our serum vitamin D levels are much lower compared to during summer.2 It is especially important to supplement vitamin D via diet and supplement during this time.

Vitamin D is a very important nutrient for our immune system.3 For example, vitamin D stimulates the expression of anti-microbial peptides in immune cells and in epithelial cells lining the respiratory tract. These peptides help protect the lung from infection.4

Pooled data from 25 randomized controlled trials involving nearly 11,000 subjects found vitamin D supplementation reduced the risk of acute respiratory tract infection. The protective effects were more evident in those who received vitamin D regularly and those who had low serum vitamin D at baseline.5

Maintaining healthy vitamin D levels helps support immune function in the long term. However, please note there are no studies investigating the effect of vitamin D on the immune response to the novel coronavirus. There is no clinical evidence showing vitamin D helps prevent, reduce, or treat COVID-19 infection.


  1. Jolliffe DA et al. J Steroid Biochem Mol Biol. 2013;136:321-329.
  2. Barger-Lux MJ et al. J Clin Endocrinol Metab. 2002;87(11):4952- 4956.
  3. Baeke F et al. Curr Opin Pharmacol. 2010;10(4):482-496.
  4. Cannell JJ et al. Epidemiol Infect. 2006;134(6):1129-1140.
  5. Martineau AR et al. BMJ. 2017;356:i6583.


Lewis Chang, PhD is Scientific Editorial Manager of R&D at Metagenics. Dr. Chang received his PhD in Nutritional Sciences at University of Washington, along with his MS in Nutrition and Public Health from Teachers College, Columbia University and BS in Pharmacy from National Taiwan University. Prior to joining Metagenics, he conducted dissertation research and completed a research assistantship and postdoctoral fellowship at the Fred Hutchinson Cancer Research Center in Seattle, WA. Dr. Chang has authored or co-authored and managed the publication of over 30 peer-reviewed journal articles and numerous scientific abstracts and posters. He has quite a green thumb, enjoys opera, theater and jazz, and loves cooking, collecting art, and learning to play gypsy jazz guitar.

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