Vitamin A is a group of substances that includes retinol, retinal, retinotic acid, beta-carotene and other retinoids and carotenoids. Vitamin A is mostly associated with vision, but it also acts as an anti-oxidant and performs other essential functions, including supporting immunity. Accordingly, the body uses vitamin A in addition to other nutrients to fight viruses.
Immunity
Your body needs vitamin A to maintain a normally functioning immune system. Specifically, the body uses retinol to support mucosal and skin cells, which are the body's first line of defense against infection. Moreover, the body uses retinoic acid to produce white blood cells, which attack or help direct attacks against pathogens and foreign matter. In fact, a deficiency in vitamin A can be considered an acquired immunodeficiency disease, much like AIDS, according to the Linus Pauling Institute. Deficiencies in vitamin A, particularly in children, usually result in higher infection rates and even death from common ailments like diarrhea and measles.
Disease Treatment
Pharmacological doses of the types of vitamin A, specifically known as retinoids, are available to treat various conditions, but none of these treatments are specifically for viruses. Therefore, although vitamin A contributes to fighting viruses, this is not a specific application. Instead, it indirectly helps fight viruses by supporting the immune system. Therefore, vitamin A is not antiviral, per se. It is pro-immunity, which is necessary to both fight and prevent viral infections, as well as infections from other pathogens.
Varying Potencies
Vitamin A has varying degrees of potencies, depending on whether you're deriving it from food or a supplement and the type of vitamin A it is specifically. For example, the body does not absorb beta-carotene as easily as it does retinal and retinol. Moreover, your body must convert beta-carotene into retinal and retinol to use it. The resulting amount of retinal and retinol depends on the source of the beta-carotene. For example, beta-carotene derived from food produces a much lower proportion of retinol, with an output ratio of 12 to 1. Beta-carotene from a supplemental oil, on the other hand, produces retinol with an output ratio of 2 to 1, which is still low, but significantly higher than from food.
Bottom Line
Your body does use vitamin A to fight viruses, so in that way, it does help. However, this relationship is indirect. Rather than actually fighting viruses, vitamin A helps support immunity, so your body is better equipped to fight viruses. Therefore, there is no benefit to consuming vitamin A specifically to fight a virus, unless you are initially deficient of the vitamin.
Moreover, there is no benefit to consuming more than the recommended daily dose. In fact, it could be harmful. Speak to your doctor about how you should integrate vitamin A into your diet, especially as a supplement. The recommended daily dose of vitamin A is 900 mcg for men and 700 mcg for women. Food sources of vitamin A include eggs, dairy, sweet potatoes, cantaloupe, carrots, spinach, kale, broccoli, collard greens, pumpkin, butternut squash, cod liver oil and fortified breakfast cereals.
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