Vitamin A
Healthy eyes.
What is it?
Vitamin A is a term for a group of fat-soluble nutrients found in animal and plant sources. Animal sources include the preformed vitamin A, or ‘retinol’, and plant (fruit and vegetable sources) include ‘provitamin A carotenoid’. Provitamin A carotenoids include alpha-carotene and beta-carotene which are converted to retinol.
Carrots are known as a healthy vegetable, they are ones that can help with night vision. What gives carrots their distinguishable orange color is beta-carotene. As a precursor to vitamin A, it can support overall eye health.
It’s also important to note that there are other types of carotenoids. These include lycopene, lutein, and zeaxanthin. While they do not convert to vitamin A, they are carotenoids that have important health functions.
What other names is it known by?
Retinol
Retinyl esters
Axerophthol
Provitamin A carotenoid (Beta-carotene)
Tretinoin
Isotretinoin
Alitretinoin
What does it do?
Vitamin A has several important functions in the body. It supports vision, fertility, growth and development in utero, immunity, maintaining cellular integrity, and supporting differentiation of cells. It can help stimulate the production and activity of white blood cells, takes part in bone remodeling, and maintains the health of the cells that line the outside of the body and intestinal tract.
Evidence suggests that eating a diet rich in fruit and vegetable sources of vitamin A may prevent cancer, cognitive decline, and age-related vision diseases.
Retinol reaches the skin following its absorption in the body. The way it does this, and the form(s) it arrives in is very complex, however just know that Retinol reaches the skin. Skin cells also have the ability to convert beta-carotene into metabolites of vitamin A, for use in the skin. That means that topical application of beta-carotene may serve as a precursor to the skin’s version of vitamin A.
The role that Vitamin A plays in skin health relates to its ability to prevent UV-induced skin damage, decrease photo-aging, help with wound healing, and treat acne. Metabolites of vitamin A have been used for decades to treat various skin conditions, like acne. One potential mechanism of action is that the topical retinol induces synthesis of collagen in the skin.
Topical retinol (from the dermatologist) has been associated with something called “retinoid dermatitis”, or a specific skin irritation. A doctor may prescribed something else if this is experienced during use. An oral vitamin A derivative (isotretinoin), also known as Accutane, is typically used for severe acne that does not respond to other treatments. This drug must be used under doctor supervision and works to reduce the amount of sebum the skin produces.
When it comes to gut health, vitamin A is known as an “anti-infective agent” which plays a role in the healthy regulation of the gut’s immune system. It is essential for maintaining consistent immunity, balance of the gut microbiome, and integrity of the intestinal epithelium. What does that mean? It can strengthen the cellular barrier that is in the gut to prevent something called ‘leaky gut’.
The gut also regulates how much vitamin A is metabolized into its various forms and where it is sent. The ability of the gut to do this declines if an infection is present. Having a healthy level of vitamin A in the body may help strengthen the gut to prevent infections.
Where to get it?
The recommended daily allowance for vitamin A is now given in mcg Retinol Activity Equivalents (RAE) which helps to account for the different bioactives of retinol and provitamin A carotenoids, all of which need to be converted in the body to retinol. RAE's are provided in the chart below.
Vitamin A can be found in both animal and plant sources. Vitamin A is usually added to foods like milk, margarine, and ready to eat cereals to support fortification and intake.
The majority of Vitamin A consumed in the US comes from preformed sources (animals), while a good percentage of intake among kids is coming from fortified foods. Leafy greens, fruits, and vegetable, are a great and healthy way to consume vitamin A.
When consuming preformed Vitamin A, the body can absorb anywhere from 75-100% of it as retinol. When consuming the provitamin A carotenoids, the bioavailability is less, however cooking methods may increase its bioavailability in the body. Most of the body’s vitamin A absorption takes place in the small intestine.
How much is needed?
In the US, the RDA is as follows:
*Adequate Intake
Deficiency is rare in western countries however when present may lead to chronic fatigue, infections, and infertility. Signs of vitamin A deficiency include a severe dryness of the eye (xerophthalmia), night blindness, irregular white patches on the whites of the eyes, and dry skin or hair. People who have compromised digestion from conditions such as Crohn’s, celiac, alcoholic cirrhosis, and cystic fibrosis may be at risk for vitamin A deficiency due to issues with absorption.
Toxicity is actually more common that deficiency due to an increased intake from preformed sources of vitamin A from supplements, for example. As a fat-soluble vitamin, any amount that is not immediately needed by the body will be stored in fat tissue or the liver. When too much becomes stored, it can become toxic. The tolerable upper intake (the highest level that is still thought to be safe) for preformed Vitamin A is 3,000 mcg for adults 19 years and older (this level is much lower for younger people). There is some evidence that suggests vitamin A at those levels may contribute to bone fractures and birth defects. Other signs of vitamin A toxicity include:
Blurry vision
Vitamin D deficiency signs (due to Vitamin A interfering with the beneficial effects of vitamin D)
Pain in the bones
Dry skin
Nausea and vomiting
Sensitivity to light.
It should be noted that the above refers to preformed vitamin A. Beta-carotene has not been found to be toxic, even at high levels. Something that can be done to ensure vitamin A toxicity isn't a concern is to choose a dietary supplement that has beta-carotene as the source of Vitamin A and opt to get vitamin A from fresh fruits and vegetables!
Also of note:
Cod Liver Oil may be a source of vitamin A. Checking the labels is a good way to determine if too much vitamin A is being consumed.
There has been some concern regarding the use of moisturizers, sunscreens, lip balms, etc. that may contain Vitamin A. It’s been found that these generally do not enter the blood stream, so they should not contribute to toxicity. Check with your dietitian or doctor, and consider getting a blood test to ensure your levels of Vitamin A are within normal limits. And note that using topicals that contain vitamin A may make your skin more sensitive to UV rays, so it’s generally recommended to use these at nighttime.
How to get it in the daily diet?
Consider adding the below to meals to get vitamin A from a variety of sources, the majority of which would be plant-based foods!
Breakfast: 1 boiled egg = 75 mcg
Lunch: ½ cup raw carrots on salad = 459 mcg
Dinner: baked sweet potato = 1,403
Total: 1,937 mcg of which 96% are from provitamin A carotenoids (the vegetables above)!
References:
Angelo, Giana. (2012). Vitamin A and Skin Health. Oregon State University, Linus Pauling Institute. Retrieved from https://lpi.oregonstate.edu/mic/health-disease/skin-health/vitamin-A
DSM Nutritional Products. (2020). Vitamins Basics. Retrieved from https://www.dsm.com/content/dam/dsm/human-nutrition/pdfs/vitamin-basics.pdf
Harvard T.H. Chan School of Public Health. (n.d.). The Nutrition Source: Vitamin A. Retrieved from https://www.hsph.harvard.edu/nutritionsource/vitamin-a/
Iyer, N., & Vaishnava, S. (2019). Vitamin A at the interface of host-commensal-pathogen interactions. PLoS pathogens, 15(6), e1007750. https://doi.org/10.1371/journal.ppat.1007750
U.S. Department of Health & Human Services, National Institutes of Health, Office of Dietary Supplements. (2021). Vitamin A and Carotenoids. Retrieved from https://ods.od.nih.gov/factsheets/VitaminA-HealthProfessional/