Did you know that nearly every vitamin has different forms? These different forms can have different functions, be absorbed better or worse, and have different potencies. Vitamin A is one such vitamin!
Although vitamin A and beta carotene are used interchangeably, they exert different functions and are not even present in the same kinds of food! Learn the major differences between vitamin A and beta carotene to accurately eat your way to good eyesight once and for all.
Vitamin A Versus Beta Carotene
In reality, vitamin A is an umbrella term for a group of fat-soluble compounds. These vitamin A compounds are found in animal and plant foods and come in two different forms – preformed vitamin A and provitamin A.
Found only in animal foods and some fortified foods and supplements, preformed vitamin A is the active form of the vitamin and includes the compounds retinol, retinal, and retinoic acid. This is considered an essential nutrient, whereas beta-carotene technically is not, though, it certainly improves health outcomes.
On the other hand, provitamin A is an inactive form found only in plant foods. Provitamin A includes carotenoids like alpha-carotene, beta-carotene, and ceta-cryptoxanthin but must be converted into one of the active forms mentioned right above for it to be useful. For example, the most common carotenoid, beta-carotene, is converted to retinol in the small intestine.
Keep in mind that there are other types of carotenoids found in some foods that are not converted into vitamin A and include lutein, lycopene, and zeaxanthin. In addition, the carotenoid forms of vitamin A, especially beta-carotene are considered antioxidants, but vitamin A as a whole is not.
Vitamin A used to be measured in IUs, however, the Institute of Medicine switched to measuring it in micrograms (mcg) of retinol activity equivalents (RAE). This measure accounts for the different absorption rates of preformed vitamin A versus provitamin A.
Thus, the recommended dietary allowance (RDA) for adults 19 years and older is 900 mcg RAE (3000 IU) for men and 700 mcg RAE (2333 IU) for women.
Vitamin A also has an upper tolerable limit (UL) of 3000 mcg of preformed vitamin A. UL stands for the maximum daily intake that is unlikely to cause harmful health effects. Because vitamin A is a fat-soluble vitamin that can accumulate in fat tissue, there is a risk of toxicity.
Comparatively, water-soluble vitamins do not pose risk for toxicity since the extra is excreted via urine.
Interestingly, vitamin A toxicity is more common than a deficiency in the U.S. This is generally related to the high doses of preformed vitamin A in supplements.
The toxicity of vitamin A is a concern because it can interfere with the beneficial functions of vitamin D (which many Americans are already deficient in) and symptoms include:
• Vision changes/blurry vision
• Bone pain
• Nausea and vomiting
• Dry skin
• Sensitivity to light
• Birth defects in infants/children
Perhaps even more interesting is that beta-carotene is not toxic to most people even at high intake levels. The body will only convert beta-carotene into preformed vitamin A only as needed, so there is little need to monitor intake.
For this reason, many supplements now include beta-carotene instead of the active preformed isomer. However, some research shows that smokers do need to monitor beta-carotene intake because high consumption has been correlated with an increased risk of lung cancer.
As mentioned, deficiency is rare in Western Countries. Those who eat a very limited amount of foods, those on a super low-fat diet, and those with any condition that interferes with normal digestion like celiac disease, Crohn's, cirrhosis, or cystic fibrosis are most at risk of developing a deficiency.
The most common signs include:
• Susceptibility to infections
• Dry skin and hair
• Xerophthalmia - severe dryness of the eyes that can eventually lead to blindness
• Nyctalopia - night blindness
• Irregular patches on the white of the eyes
Vitamin A (Preformed) Food Sources
Preformed vitamin A foods are all derived from animals or fortified.
1. Beef liver
2. Red meat
4. Fish and seafood
7. Fortified cereals, breads, juices, and dairy
Provitamin A/Beta Carotene Foods
Plants, particularly fruits and vegetables, are the only food sources of beta carotene, the inactive, antioxidant form. Fun fact- beta carotene is what gives foods, particularly fruits and vegetables, their vibrant red and orange color!
2. Sweet potatoes
4. Winter squashes
7. Red and orange bell pepper
10. Summer squash
11. Leafy greens like kale and spinach but also broccoli
12. Fortified foods
Health Benefits of Vitamin A
The functions of vitamin A as a group will be discussed before providing a few unique functions of beta-carotene.
Parents frequently tell their kids to eat carrots to help them see. While this is somewhat true, it is a bit more complicated.
Vitamin A is essential for preserving eyesight, but the preformed version actually just prevents night blindness. It is needed to convert the light that hits the retina into an electrical signal that is sent to the brain.
On the other hand, beta-carotene is specifically responsible for slowing the age-related decline in eyesight. Age-related macular degeneration (AMD) is the leading cause of blindness in the world and is most likely caused by oxidation damage to the retina. Because beta-carotene serves as an antioxidant, scientists believe this is how it helps prevent the decline in eyesight.
Healthy Immune System
Vitamin A helps the body maintain natural immune defenses because it is part of the mucous barriers in the eyes, lungs, gut, and genitals. They essentially trap bacteria, toxins, and other infectious agents.
In addition, vitamin A is involved in the production and function of white blood cells, which also capture and clear bacteria and other pathogens from the bloodstream. This is why a vitamin A deficiency will result in increased susceptibility to infections.
Ladies, how many of you use retinol as part of your beauty routine to prevent acne? Little did you know that those retinol creams were concentrated with vitamin A though!
While the relationship is not fully understood, some research shows that vitamin A deficiency causes an overproduction of the protein keratin in hair follicles. This overproduction would make it more difficult for dead skin cells to be removed by hair follicles and increase the risk of acne because they would remain clogged.
Isotretinoin is a popular oral retinoid that has been shown to be effective at treating severe acne. But because of its side effects, it should only be taken under supervision from a professional.
Although the connection between vitamin A and bone health is not well understood, numerous studies simply show a correlation with deficiency or toxicity and increased risk of fractures. This seems to be a pattern with the first chronological vitamin and is similar to its role in preventing cancer as you will learn shortly.
Nonetheless, it probably exerts bone function simply because vitamin A plays a role in cellular growth and development. Indeed, studies show those with lower levels of vitamin A and those that consume too much preformed vitamin A have more chance of fractures.
Balance is the name of the game when it comes to vitamin A!
Fertility Support and Growth/Development
Not only is vitamin A essential for maintaining fertility, but it is also vital for the normal growth and development of embryos during pregnancy.
Vitamin A deficiency is linked with the underdevelopment of sperm cells, which causes infertility. Likewise, inadequate vitamin A in females may reduce the quality of the egg, which can impact the implantation in the womb.
Furthermore, vitamin A is involved with the development of major organs and structures in a growing fetus including the skeleton, nervous system, heart, kidneys, eyes, lungs, and pancreas.
Prevention Against Some Cancers
Because vitamin A plays a role in the growth and development of different cells, this has implications for cancer, since this is a disease of uncontrollable cell growth or division!
However, while higher beta-carotene intake from plant foods is linked with decreased risk of bladder, cervical, lung, and Hodgkin's lymphoma cancers, this is not the case with the preformed vitamin A found in animal foods.
In addition, supplement forms of vitamin A and/or beta-carotene do not seem to exert similar effects either, and some studies actually show an increased risk for cancer from supplementation!
Thus, the best way to harness this potential power is by eating enough beta-carotene from plant foods.
Antioxidant Functions of Beta Carotene
Beta-carotene is unique in that it serves as an antioxidant, meaning it can stabilize free radicals. These are molecules that cause oxidative stress to cells and tissues if they accumulate within the body.
This unique function makes beta-carotene important in preventing chronic diseases associated with oxidative damage such as… Well all of them! Beta-carotene is especially important for reducing the risk of heart disease, obesity, type 2 diabetes, and stroke.
Furthermore, some evidence shows beta-carotene is involved in reducing cognitive decline, although the mechanism is not well understood yet. Adequate intake is associated with reducing the risk of dementia, Alzheimer's, and Parkinson's disease.
Referred to in the mainstream as one vitamin, Vitamin A is really a group of varying compounds.
The active form is called Preformed vitamin A and is found in animal sources and some fortified foods while the inactive form is provitamin A found in plants, especially red and orange ones. The most well-known isomer of provitamin A is beta-carotene, which is an antioxidant.
While preformed vitamin A poses a toxicity risk, provitamin A consumption does not because the body will only convert beta-carotene into the active form as needed. However, smokers do need to monitor beta-carotene intake as some studies show it increases the risk for lung cancer. Interestingly, beta-carotene may be protective against lung cancer in those who do not smoke.
Finally, other main functions of vitamin A include night vision, supporting a healthy immune system, and supporting skin bone, and fertility health among others.
Olsen N. Benefits of Beta Carotene and How to Get It. Healthline. Updated August 13, 2020. https://www.healthline.com/health/beta-carotene-benefits#benefits.
The Nutrition Source – Vitamin A. Harvard T.H. Chan. https://www.hsph.harvard.edu/nutritionsource/vitamin-a/.
West H. 6 Health Benefits of Vitamin A, Backed by Science. Healthline. Written August 23, 2018. https://www.healthline.com/nutrition/vitamin-a-benefits#TOC_TITLE_HDR_7.