Vitamin D , Immunity and The Gut

Vitamin D deficiency is common affecting over half of the U.S. population. Populations living up North and not getting sun exposure may be more at risk for vitamin D deficiency. People who do not get outdoors are also at risk such as nursing home residents or healthcare workers. African Americans and Hispanic populations in the U.S have a high rate of vitamin D Deficiency (1).  A new study in the Journal of American Medical Association by David Meltzer in the Department of Medicine at the University of Chicago links low Vitamin D status to risk of COVID 19 infections. (2).

After reading this study in it’s entirety, it is unclear whether extra vitamin D can decrease the incidence of COVID 19. Vitamin D does strengthen immunity and affects zinc metabolism- also important in immune defense. More studies with larger cohorts, randomized studies need to be conducted to determine if Vitamin D plays a definitive role in COVID 19 and it’s risk of infection.Just as important to know- a high mega dose of Vitamin D in patients hospitalized for COVID 19- did NOT shorten their stay in the hospitals(3).

Other studies point to Vitamin D playing a role in diversifying the gut microbiome. After Vitamin D supplementation a study showed an increase in Bacteroidetes ( beneficial gut microbe) and a decreased Firmicutes. This ratio change has been seen in other studies to result in improved gut permeability and inflammation for improvement in gut health (4).

Vitamin D is found in fortified foods such as dairy products and orange juice , salmon, sardines and mushrooms. Even getting out in the sun shine for an hour can boost vitamin D levels.

In the meantime, should we be taking Vitamin D Supplements? Since many of us have been in lock down and getting less outdoor exposure to the sun this last year- taking a Vitamin D supplement of 25mcg/ 1,000 IU/day may be helpful. In addition, being over 50 years of age places one at risk for thinning of the bones. Vitamin D can help with calcium absorption, an integral mineral needed to keep the infrastructure of the bone strong. So overall, yes a little extra Vitamin D supplementation may not be a bad idea!


  1. Forrest KY, Stuhldreher WL. Prevalence and correlates of vitamin D deficiency in US adults. Nutr Res. 2011 Jan;31(1):48-54. doi: 10.1016/j.nutres.2010.12.001. PMID: 21310306.
  2. Meltzer DO, Best TJ, Zhang H, Vokes T, Arora V, Solway J. Association of Vitamin D Status and Other Clinical Characteristics With COVID-19 Test Results. JAMA Netw Open. 2020;3(9):e2019722. doi:10.1001/jamanetworkopen.2020.19722
  3. Murai IH, Fernandes AL, Sales LP, et al. Effect of a Single High Dose of Vitamin D3 on Hospital Length of Stay in Patients With Moderate to Severe COVID-19: A Randomized Clinical Trial. JAMA. 2021;325(11):1053–1060. doi:10.1001/jama.2020.26848
  4. Singh, P., Rawat, A., Alwakeel, M. et al. The potential role of vitamin D supplementation as a gut microbiota modifier in healthy individuals. Sci Rep 10, 21641 (2020).