When boosting the immune system or providing protection against viruses, not many people think of vitamin A. It is well known that vitamin A levels plummet with infection and with chemical exposure. There are some studies that show it to be of value in protecting against viral infections.
There are a number of animal studies showing vitamin A as antiviral. One study (Int J Vitam Nutr Res. 2010 Apr;80(2):117-30), showed that it alleviated inflammatory responses in reproductive tracts of male mice infected with pseudorabies virus. Another animal study (Vaccine. 2014 May 7;32(22):2521-4), showed that improves IgA production in the mucosa. Vitamin A deficient mice have increased viral antigens and enhanced cytokine/chemokine production in nasal tissues following respiratory virus infection, according to another study (Int Immunol. 2016 Mar;28(3):139-52).
Human studies exist as well. One study (Kansenshogaku Zasshi. 1999 Feb;73(2):104-9.) showed supplementation to be helpful for both measles and RSV. There are several studies involving HIV infected children and vitamin A. One study (Nutrition. 2005 Jan;21(1):25-31.), demonstrated a reduction in mortality in HIV infected children. Another study (J Nutr. 2019 Oct 1;149(10):1757-1765), showed that vitamin A supplementation reduced mortality in patients infected with Ebola virus. Supplementation with vitamin A may potentiate vaccines. In one study (Viruses. 2019 Sep 30;11(10)), researchers concluded, “Overall, our study demonstrates that vitamin A&D supplementation can improve immune responses to vaccines when children are vitamin A and D-insufficient at baseline. Results provide guidance for the appropriate use of vitamins A and D in future clinical vaccine studies.”
Vitamin A is important for membrane health. One study(J Nutr Biochem. 2010 Mar;21(3):227-36), looked at alveolar membranes in rats. Researchers concluded, “Vitamin A deficiency results in alterations of the structure and composition of the alveolar BM which are probably mediated by TGF-beta1 and reverted by retinoic acid.”
In another animal study (PLoS One. 2015 Sep 30;10(9):e0139131), researchers stated, “In conclusion, vitamin A deficiency suppressed the immunity of the airway by decreasing the IgA and mucin concentrations in neonatal chicks. This study suggested that a suitable level of vitamin A is essential for the secretion of IgA and mucin in the respiratory tract by regulating the gene expression of cytokines and epithelial growth factors.”
Vitamin A and vitamin D are important for the health of the gut membrane. So much so, that deficiency can affect the microbiota, and thus the immune system. Researchers in one study (Crit Rev Biochem Mol Biol. 2019 Apr;54(2):184-192) state, “There are some unique functions of vitamin A and D; for example, vitamin A induces gut homing receptors on T cells, while vitamin D suppresses gut homing receptors on T cells. Together, vitamin A- and vitamin D-mediated regulation of the intestinal epithelium and mucosal immune system shape the microbial communities in the gut to maintain homeostasis.”