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The Importance of Vitamin A
Vitamin A is important for good vision, skin, and immune function, healthy babies, and overall health. But knowing whether you’re getting enough, or too much, can be tricky.
On one hand, the federal government has concluded that a deficiency of vitamin A is so rare that in 2020, when new food labels come into effect, vitamin-A content no longer needs to be listed. On the other hand, analyses of government nutritional surveys by independent researchers, such as those at the Medical University of South Carolina in Charleston, have found that more than one-third of teens and adults fall short on vitamin A.
In calculating the shortfall, researchers considered natural food sources, fortified foods, and dietary supplements. Not eating enough foods rich in vitamin A is one reason for low vitamin A, and conditions that reduce absorption of nutrients, such as celiac, Crohn’s, or other inflammatory digestive diseases, are another. Equally important, it’s also possible to get too much vitamin A, which can lead to liver abnormalities and birth defects.
Forms of Vitamin A
There are two forms of vitamin A found in food and supplements:
Preformed vitamin A from animals:
Often listed as retinyl acetate or retinyl palmitate on supplement labels, this form is found in animal foods. Top sources include fish liver oil and animal livers. Eggs, dairy products, salmon, and herring contain smaller amounts. High-dose preformed vitamin A can be toxic.
Did You Know?
Pastured egg yolks and grassfed dairy are two of the best vegetarian sources of preformed vitamin A.
Provitamin A carotenoids from plants:
This form of vitamin A doesn’t become toxic, even at high doses. Top sources in the American diet include carrots, broccoli, sweet potatoes, cantaloupe, kale, and squash, but provitamin A is also found in many other fruits and vegetables. In supplements, beta-carotene is the main source of this form, but some products also contain alpha-carotene and beta-cryptoxanthin, other carotenoids that are converted to vitamin A.
How Vitamin A Doses Are Measured
Quantities of vitamin A have traditionally been expressed in international units (IU). But the measurement is changing to micrograms of retinol activity equivalents (RAE). It sounds complex but there’s a reason for the change: to more accurately represent the effects of different vitamin A forms and doses.
Retinol is the building block for active vitamin A, and it’s naturally present in preformed, animal-based vitamin A in food and supplements. After being ingested, retinol is converted to active vitamin A that can be stored in the liver and used as needed.
With plant-based vitamin A, beta-carotene and other carotenoids must first be converted to retinol, and then to active forms of vitamin A. To get the same amount of retinol, you need larger amounts of the plant nutrients than animal-based vitamin A.
Here’s an example: the Daily Value, or %DV in Supplement Facts labels (an approximate average daily requirement)is 900 mcg RAE. Depending on the form, this Daily Value is equivalent to any one of these:
Animal-based, preformed vitamin A
- 3,000 IU from food or supplements
Plant-based vitamin A
- 6,000 IU beta-carotene from supplements
- 18,000 IU beta-carotene from food
- 36,000 IU alpha-carotene or beta-cryptoxanthin from food
Safe Limits for Vitamin A
To avoid toxicity, the government has set a tolerable upper limit of 3,000 mcg RAE, or 10,000 IU daily, but this applies only to the preformed, animal-based form. No upper limit has been set for plant-based vitamin A, because excess amounts in the body are excreted and therefore don’t become toxic.
How to Choose Vitamin A Supplements
In real life, we get a combination of vitamin-A forms from foods. Supplements can contain one or more forms. There is a transition period for the new measurement system, so you’re likely to see some products using RAE and other using IU during the next year or so.
Unless you’re under the care of a health professional who recommends higher doses, it’s best for men to aim for about 100 percent of the Daily Value as the total from all supplements and food. For women, the daily recommended amount is 700 RAE: 77 percent of the Daily Value. If you routinely eat liver, you may not need vitamin A supplements, as a 3-oz. serving of beef liver contains more than 4 times the Daily Value.
Are you getting too much vitamin A or too little?
Here’s what to look for:
Signs of Vitamin A Deficiency
- Dry skin
- Dry eyes
- Difficulty seeing in low light
- Frequent infections, especially in the throat and chest
- Difficulty healing after injury or surgery
- Trouble getting pregnant
- Stunted growth in children
Signs of Too Much Vitamin A
- Vision changes
- Mouth ulcers
- Birth defects
Toxic levels of vitamin A are not likely to come from food, but can occur with excessive supplementation with animal-based forms of vitamin A, such as fish liver oil.