Vitamin A toxicity mainly can happen from vitamin A supplements. In some cases from food options, as well.
Why you should worry about hyperdose of vitamin A?
Vitamin A toxicity can cause (1, 2,3):
- decreased life quality,
- increased mortality rates,
- hip fracture, and even
Why this happens?
Because vitamin A accumulates in the body.
Unlike most vitamins, vitamin A can be stored within the body at relatively high levels, causing toxicity.
So, you should consult your physician, before taking vitamin A supplements.
What is vitamin A?
Vitamin A is essential for the body as it is involved in:
- immune function,
- cell growth,
- cellular communication, and
- playing a critical role in the normal formation and maintenance of the heart, lungs, kidneys, and other organs (6).
Forms of vitamin A
Vitamin A is a group of fat-soluble retinoids. Vitamin A has two forms in our diet:
- preformed vitamin A, known as retinol
- provitamin A carotenoids, known as beta-carotene
Both preformed vitamin A and provitamin A must be metabolized by the body to retinal and retinoic acid, which are the active forms of vitamin A (6).
What is Retinol?
Vitamin A is the name of a group of fat-soluble retinoids. Retinoids are vitamin A and its natural and synthetic analogs (retinal, retinyl esters, and retinoic acid).
Retinol is by definition vitamin A.
Retinyl ester is a storage form of retinol and hasn’t known biological activity aside from retinol storage. The liver and intestine are the major tissue sites of retinol esterification in the body (5). That means that vitamin A is mainly stored in the liver in the form of retinyl ester.
Retinal is needed for visual pigment formation and it is important in the visual function. In tissues, retinal serves as an intermediate in the synthesis of retinoic acid from retinol (5).
Retinoic acid is created in tissues from retinol. Retinoic acid is an active form of vitamin A (5).
Preformed vitamin A, most commonly called retinol is found in foods from animal sources, including dairy products, fish, and meat, especially the liver.
To make it clear, retinol is another name for vitamin A.
What is Beta-carotene?
Provitamin A carotenoids are commonly called beta-carotene. That’s because the most important provitamin A carotenoid is beta-carotene (6). Other provitamin A carotenoids are alpha-carotene and beta-cryptoxanthin.
The body converts provitamin A carotenoids into vitamin A.
Other carotenoids found in food, such as lycopene, lutein, and zeaxanthin, are not converted into vitamin A (6).
Provitamin A carotenoids are found only in plants.
To make it clear… Beta-carotene is converted to vitamin A in the body. Only plants contain beta-carotene, though.
Why plants can’t cause vitamin A toxicity?
The body has to convert the carotenoids (plant pigments) into vitamin A. This procedure isn’t as efficient as consuming animal sources.
In a sense, the human body hasn’t any extra work to do, when someone consumes animal products.
That’s why the vitamin A from animal sources is called preformed vitamin A.
On the other hand, plants contain beta-carotene. The human body can’t transform beta-carotene in vitamin, as effectively.
For this reason, 100 IU (International Units) of vitamin A from animal sources, aren’t equal to 100 IU of vitamin A from plants.
Vitamin A from animal origin is 6-12 times more bioactive than vitamin A from plant origin.
Moreover, vitamin A from supplements is equivalent to vitamin A from animal sources (6).
Recommended Daily Intake of Vitamin A
Recommended Daily Intake for vitamin A is given as retinol activity equivalents (RAE), not International Units (IU) (6).
|0–6 months||400 mcg RAE||400 mcg RAE|
|7–12 months||500 mcg RAE||500 mcg RAE|
|1–3 years||300 mcg RAE||300 mcg RAE|
|4–8 years||400 mcg RAE||400 mcg RAE|
|9–13 years||600 mcg RAE||600 mcg RAE|
|14–18 years||900 mcg RAE||700 mcg RAE||750 mcg RAE||1,200 mcg RAE|
|19–50 years||900 mcg RAE||700 mcg RAE||770 mcg RAE||1,300 mcg RAE|
|51+ years||900 mcg RAE||700 mcg RAE|
Retinol activity equivalents (RAE) index is created because different vitamin A sources (animal vs plant) have different bioactivity.
For instance, if you are an adult woman, you should consume 700 mcg RAE of vitamin A. If you consume meat or you’re a vegetarian, it stands for 2300 IU of vitamin A. If you a vegan, it stands for 14000 IU.
The math behind this equation:
- RDI for animal sources = RAE/0.3
- RDI for vegan sources = RAE/0.05
To make it clear… Both animal products and plants contain a form of vitamin A. But the human body produces vitamin A much easier from animal sources. BUT plants can protect, and improve eyesight in many ways.
When vitamin A toxicity can occur?
Vitamin A toxicity can occur mainly from vitamin A supplements.
If you’re vegan and don’t take vitamin A supplements you’re safe. Beta-carotene from plants has to be converted to retinol. You have to eat A LOT of carrots, to suffer from vitamin A toxicity.
Certainly, vitamin A toxicity can occur when dietary vitamin A from animal sources is combined with vitamin A supplementation.
You should consult your physician if you think that you need vitamin A supplementation. Extra care should be given to people with liver damage.
Vitamin A toxicity symptoms
Symptoms may include:
Blurred vision, vision problems, headaches, nausea, bone pain, hair loss, decreased appetite, dizziness, liver damage, and skin changes.
So, what food is the safest option for vitamin A?
The best option is a whole food plant-based diet.
It’s rich in beta-carotene, important for eye health. Plants are rich in antioxidants as well. Furthermore, fruits and vegetables are rich in lutein and zeaxanthin. Both super important for good eyesight.
Also, a diet rich in plants can’t cause vitamin A toxicity (4).
For instance, foods rich in beta-carotene are peppers, carrots, squash, turnip greens, peas, spinach, collard greens, sweet potatoes, dill weed, cress, beet greens, kale, cabbage, amaranth leaves, broccoli, arugula, and brussels sprouts.
Remember… beta-carotene is a safe source of vitamin A (7). Plants provide much much more…
- NCBI – Bookshelf – Vitamin A Toxicity
- NCBI – Pubmeb.gov – The acute and chronic toxic effects of vitamin A.
- NCBI – Pubmeb.gov – Vitamin A and Retinoids as Mitochondrial Toxicants
- NCBI – Pubmeb.gov – Evaluation of vitamin A toxicity.
- NCBI – Pubmeb.gov – Retinol and retinyl esters: biochemistry and physiology Thematic Review Series: Fat-Soluble Vitamins: Vitamin A
- National Institutes of Health (NIH) – Vitamin A Fact Sheet for Health Professionals
- NCBI – Pubmeb.gov – β-Carotene Is an Important Vitamin A Source for Humans