Vitamin A is the name of a group of fat-soluble antioxidant compounds. Two forms of the vitamin are available in the human diet: Retinoids, which are found in animal products and can be directly used by the body, and carotenoids (of which beta-carotene is the most important), which are found in plant foods and need to be converted into retinol by the body after the food is ingested.
What Vitamin A Does for Us
Maintains vision – Vitamin A is best-known for boosting our eyesight, and for good reason. When light hits the retina (the light-sensitive membrane covering the back wall of the eyeball), retinol is converted to retinal, which is then transported to rod cells. In these cells, retinal binds to a protein called opsin, altering its shape and generating nerve impulses. These nerve impulses then send signals to the brain regarding the objects in our visual field. Finally, retinal is converted back to retinol, and the cycle ends.
Without vitamin A-sourced retinal, our bodies wouldn’t be able to continue this cycle and our eyesight would rapidly degenerate. In fact, one of the earliest symptoms of a vitamin A deficiency is night blindness, or an ability to see in low light conditions. Therefore, the time-honored statement about carrots helping us see in the dark is actually true: Being rich in vitamin A (beta-carotene), carrots supply our bodies with the retinol needed to maintain our vision.
Antioxidant properties – Like vitamin C and vitamin E, vitamin A is an antioxidant that guards us from the cell-damaging effects of free radicals (rogue atoms or atomic groups). Consequently, a large number of degenerative diseases linked to unchecked free radical activity, such as cancer, arthritis, and macular degeneration, can be prevented or even treated with these important antioxidants.
Supports the immune system – The retinol form of vitamin A helps maintain the function of the cells that comprise our body’s first barrier against infection: The skin and lining that covers the digestive, respiratory, and urinary tracts. Additionally, our bodies also need vitamin A for the formation and activation of white blood cells, which are the cells of the immune system that are involved in defending our bodies from infectious diseases and foreign materials. For this reason, a body lacking in vitamin A will suffer from a compromised immune system, resulting in chronic infections.
Aids gene transcription – Our genes contain the code for vital proteins our bodies need to maintain its countless day-to-day functions. However, when these proteins are needed, the genetic code first needs to be transcribed – an action that our bodies heavily regulate. Studies have shown, however, that the retinoic acid form of vitamin A helps to regulate this rate of gene transcription, meaning that vitamin A helps maintain the entire daily functioning of our body.
Recommended Daily Intake
The recommended daily intake (RDI) of vitamin A is 900 micrograms in adult men and 700 micrograms in adult women. Dietary sources of vitamin A are far superior to supplemental sources, and meeting our RDI of vitamin A through diet isn’t difficult. In fact, vitamin A deficiencies in the developed world are rare.
Foods that are rich in retinoids include fish, fish oil, eggs, raw milk, and meat. Foods that are rich in carotenoids include sweet potato, pumpkin, spinach, kale, carrots, and squash.