Vitamin A. Retinol. Carotenes… wait what? They are the same thing, right? Vitamin A is perhaps one of the most perplexing vitamins (for me at least).
The two key forms of vitamin A in the human diet are performed vitamin A and provitamin A. Performed vitamin A, also called retinol or retinyl esters, is found in animal products, and provitamin A, also known as carotenoids, is found in plant products.
There is a lot to unpack when it comes to vitamin A, and honestly, a lot more than my bachelor’s degree knowledge allows me to do. For you and me, I have looked back on all my course notes regarding this vitamin to better understand it. I think that the most important things to note are a brief summary of what vitamin A is as a whole and as its many forms, sources of vitamin A, roles of vitamin A within the human body, and upper limits and toxicity as far as dosage and intake.
Chances are when you hear of vitamin A you think about vision. The human retina (the back inside layer of nerves and cells in the eye) has four types of vitamin A containing photopigments (a molecule or pigment that experiences a chemical change when exposed to light) that are responsible for helping us see during the day and night. Topical vitamin A application can also help in the treatment of dry eye disorders.
Aside from vision health, vitamin A also plays crucial roles in immune function, skin health, cellular integrity, reproduction, cellular communication, cellular growth, gene expression, wound healing, and many more biological functions. Vitamin A also promotes normal functioning and maintenance of many organs, such as the heart, lungs and kidneys.
Vitamin A is one of four fat-soluble vitamins in the human body (fat is needed to metabolize and “use” the vitamin). When there are excess amounts of a fat-soluble vitamin in the body it is stored. In the case of vitamin A, the liver serves as the main place of storage. The recommended dietary allowance (RDA) is the average daily intake that is recommended to meet the health needs of most healthy individuals. RDAs for vitamin A are given as retinol activity equivalents (RAE). According to the National Institutes of Health (NIH), one microgram (mcg) RAE is equal to 1 mcg retinol, 2 mcg supplemental beta-carotene, and 12 mcg dietary beta-carotene. I am assuming anyone who is reading this is probably within the age range of 19-50 years old, so the RDAs, per the NIH, for that age range of vitamin A are; 900 mcg RAE for men and 700 mcg RAE for women. If you are like me, you find this dosing information a bit weird and are probably used to thinking in international units (IU). For the sake of ease, “the RDA of 900 mcg RAE for men is equal to 3,000 IU IF the food or supplement source is performed vitamin A (retinol) or if the supplement source is beta-carotene.” (NIH, March 26, 2021). Another NIH source equated the RDA for women to 2,700 IU.
Going off the RDA information it seems important to talk about safety issues and possible toxicity associated with vitamin A. While large amounts of beta-carotene and other provitamin A carotenoids are not associated with major adverse effects, excess performed vitamin A can be toxic (hypervitaminosis A) and lead to tissue and liver damage that is not always reversible. Some studies have shown that excessive intakes of performed vitamin A can lead to decreased bone mineral density and increased fracture risk. Toxicity from topical forms of vitamin A are also possible and are most seen as skin irritation and/or peeling. There is also some concern of toxicity when it comes to pregnant women and their unborn babies, and it is recommended that unless otherwise instructed, pregnant women should avoid supplements that contain vitamin A and foods that are high in vitamin A (such as liver).
When it comes to dietary intake of vitamin A most of us (in the US at least) should be getting what we need from our food. There are many foods that are great sources of vitamin A, but a few of the foods that offer the highest amounts are liver (beef and chicken), chili peppers, carrots, apricots, collard greens, sweet potatoes, spinach, kale, mangos and broccoli. Vitamin A deficiency may be due to inadequate dietary intake, poor absorption, storage, transportation, or some combination of these.
Vitamin A deficiency can stop the production of those photopigments that were mentioned earlier, which can lead to night blindness and an under-nourished eye. According to the American Academy of Ophthalmology, vitamin A deficiency is the leading cause of preventable blindness in children worldwide. I remember watching a documentary in a medical anthropology course about night blindness in children. So many of these children lost their sight at night and were getting hurt or dying because of it. After searching and searching for a reason why these children couldn’t see at night, vitamin A came to light. Injections of vitamin A were administered, and vision returned almost instantly. Vitamin A deficiency is most prevalent in developing nations. From blindness to dry skin and lips, and impaired immunity and growth retardation, there can be many different signs and symptoms of a vitamin A deficiency.
This post could go on and on as the information about vitamin A is seemingly endless. If you are like me, you are a bit of a health and wellness nerd, and you enjoy learning and reviewing. As I mentioned earlier, I am not a medical professional and don’t mean to act as one. I simply enjoy broadening my knowledge and figured that others may want to learn with me. I think that it would be fun to do sort of a micronutrient series as I review some of my course notes and explore new information. If you are someone who can fill in the gaps or has some thoughts, PLEASE do share them with me and others who may be reading this.
Intuitive Health & Living 