How does Vitamin A Help your Immune System?

By: Leigh Matthews

When we think about immune-supportive nutrients, we often think of vitamin C, maybe even vitamin D, but what about vitamin A? This sometimes overlooked nutrient used to be called the “anti-infective” vitamin as it is essential for a healthy immune system. In addition to offering antioxidant benefits, vitamin A plays a number of key roles in the maintenance of good health.

What is vitamin A?

It might sound like a silly question, but vitamin A isn’t a single vitamin. Instead, vitamin A is a group of fat-soluble vitamins that includes retinal, retinol, and retinyl palmitate. These act as cofactors in numerous biochemical reactions in the body, including those vital for healthy vision and cellular growth.<1>

Unlike vitamin C, which is water soluble, vitamin A is fat soluble. This means that it is best absorbed in the presence of dietary fat. It also means that vitamin A can be stored in the body, which offers benefits and the potential for toxicity if too much is taken all at once or over a longer period of time.

Retinol is the main form of vitamin A circulating in the human body, but retinyl palmitate is the primary storage form of the nutrient and is the most stable vitamin A ester available.<2> <3>

Retinyl palmitate is also the predominant form of the nutrient in the skin and affects skin aging, immune defence, and wound healing.<4> Indeed, all retinoids play a role in regulating cellular division and differentiation to produce the normal stratified architecture of the skin. Retinyl palmitate has been given generally recognized as safe (GRAS) status, and is routinely used to treat acne, psoriasis, skin keratinization disorders, and photodamage.<5>

Vitamin A is also an antioxidant nutrient with free radical scavenging potential, and can absorb the type of ultraviolet (UV) light responsible for most of the damaging effects of sun exposure.

Supporting skin health, vision, and cellular metabolism aren’t the only tricks vitamin A has up its sleeves. This nutrient is also essential for immune system activity.

How does vitamin A support immune function?

Vitamin A is critical for healthy immune system activity. But, before we even get to the “infection-fighting” activities of the nutrient, vitamin A is critical for healthy epithelial tissue. This is the layer of tissue that lines the nose, throat, mouth, eyes, lungs, and intestines, and it is our first line of defence against invading pathogens like viruses. Vitamin A helps with the secretion of mucous in those tissues, and that mucous carries antibodies that help protect against infection.

Vitamin A also supports immune function by supporting the development, differentiation, and activation of white blood cells, such as lymphocytes. It also influences T and B cells, immunoglobulin-A, intestinal immune responses, and inflammatory activity.<6> <7> In particular, retinoic acid is necessary to maintain sufficient levels of natural killer cells and for the production of cytokines, such as interleukin 1 (IL-1).<8>

Vitamin A may also improve anemia in people who are deficient in iron and vitamin A, and iron is another key nutrient in immune function. <9>

Where can you get vitamin A?

Regular vitamin A intake is essential for good health, but the main dietary source of vitamin A is animal liver, which doesn’t appeal to everyone. Thankfully, we can also create our own vitamin A from some 50 carotenoids found in plant foods such as sweet potatoes, squash, carrots, cantaloupe, and spinach.

The vitamin A content of foods is measured in retinol activity equivalents (RAE). To get 1 mcg RAE from food, you need to consume 12 mcg of beta-carotene. In contrast, just 2 mcg of beta-carotene from supplements offer the equivalent of 1 mcg RAE.<10> This is helpful because the capacity to convert carotenoids into vitamin A may have been overestimated and can differ between individuals.<11> However, even those who are “low responders” to beta-carotene can still convert some to vitamin A.<12>

Still, the best way to ensure a sufficient intake of vitamin A is to get it directly from foods such as fatty fish or halibut oil, such as in Natural Factors Vitamin A 10,000 IU. Or, if you’re vegan, vegetarian, or otherwise don’t eat fish or animal liver products, a beta-carotene supplement is a good idea.

Anyone who is pregnant or who may become pregnant should not use products containing pre-formed vitamin A due to an increased risk of birth defects. Retinol is also contraindicated in individuals with a compromised liver, hepatitis, or any liver disease.

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<1> Stargrove MB, Stargrove LB. Herb, nutrient and drug interactions: clinical implications and therapeutic strategies. St. Louis, Missouri: Mosby Elsevier. 2008.

<2> Sorg O, Tran C, Saurat JH. Cutaneous vitamins A and E in the context of ultraviolet- or chemically-induced oxidative stress. Skin Pharmacol Appl Skin Physiol. 2001; 14:363-72.

<3> National Institutes of Health, Office of Dietary Supplements. Vitamin A Fact Sheet for Health Professionals. Available from: https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/#en2

<4> Fu PP, Xia Q, Boudreau MD., et al. Physiological role of retinyl palmitate in the skin. Vitam Horm. 2007;75:223-56.

<5> Shapiro SS, Seiberg M, Cole CA. Vitamin A and its derivatives in experimental photocarcinogenesis: preventive effects and relevance to humans. J Drugs Dermatol. 2013; 12:458-63.

<6> Mora JR, Iwata M, von Andrian UH. Vitamin effects on the immune system: vitamins A and D take centre stage. Nature Reviews. Immunology.2008; 8:685-98.

<7> Czarnewski P, Das S, Parigi SM, et al. Retinoic Acid and Its Role in Modulating Intestinal Innate Immunity. Nutrients. 2017; 9:pii:E68.

<8> Food and Nutrition Board, Institute of Medicine. Dietary Reference Intakes for Vitamin A, Vitamin K, Arsenic, Boron, Chromium, Copper, Iodine, Iron, Manganese, Molybdenum, Nickel, Silicon, Vanadium, and Zinc. Washington, DC: National Academy Press, <2001> Available from: https://www.ncbi.nlm.nih.gov/books/NBK222310/

<9> Linus Pauling Institute – Vitamin A. (2011). Available from: http://lpi.oregonstate.edu/mic/vitamins/vitamin-A. <2008>

<10> National Institutes of Health. <2020>. Vitamin A Fact Sheet for Health Professionals. Available from: https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/#h3

<11> Lietz G, Oxley A, Leung W, et al. Single nucleotide polymorphisms upstream from the β-carotene 15,15′-monoxygenase gene influence provitamin A conversion efficiency in female volunteers. J Nutr. 2012; 142:161S-5S.

<12> Borel P. Genetic variations involved in interindividual variability in carotenoid status. Mol Nutr Food Res. 2012; 56:228-40.