Why a plant-based diet won’t cause vitamin A toxicity?

vitamin A toxicity symptoms from supplements
Vitamin A plant sources.

Vitamin A toxicity mainly can happen from vitamin A supplements, and foods rich in retinol.

What vitamin A toxicity can cause?

Unlike most vitamins, vitamin A can be stored in the body at relatively high levels, causing toxicity. Vitamin A toxicity can cause (1, 2,3):

  • decreased life quality,
  • increased mortality rates,
  • osteoporosis,
  • hip fracture, and even
  • teratogenicity.

So, you should consult your physician, before taking vitamin A supplements.

What does vitamin A do to the body?

Vitamin A is essential for the body as it is involved in:

  • immune function,
  • cell growth,
  • vision,
  • differentiation,
  • reproduction,
  • 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 carotenoid, known as beta-carotene

Both preformed vitamin A and provitamin A must be metabolized by the body to 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 intestines 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.

What is Beta-carotene?

Provitamin A carotenoid is 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.

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 source foods.

On the other hand, plants contain beta-carotene. The human body can’t transform beta-carotene to vitamin A as effectively.

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 source foods (6).

Recommended Daily Intake for Vitamin A

Recommended Daily Intake for vitamin A is given as retinol activity equivalents (RAE) (6).

AgeMaleFemalePregnancyLactation
0–6 months400 mcg RAE400 mcg RAE  
7–12 months500 mcg RAE500 mcg RAE  
1–3 years300 mcg RAE300 mcg RAE  
4–8 years400 mcg RAE400 mcg RAE  
9–13 years600 mcg RAE600 mcg RAE  
14–18 years900 mcg RAE700 mcg RAE750 mcg RAE1,200 mcg RAE
19–50 years900 mcg RAE700 mcg RAE770 mcg RAE1,300 mcg RAE
51+ years900 mcg RAE700 mcg RAE  

Retinol activity equivalents (RAE) index is created because different vitamin A sources (animal vs plant) have different bioactivity.

When vitamin A toxicity can occur?

Vitamin A toxicity can occur mainly from vitamin A supplements and beef liver. The upper safe dosage for vitamin A is 3,000 mcg.

On the other hand, plants don’t cause 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 before taking supplements.

Vitamin A toxicity symptoms

Symptoms may include blurred vision, headaches, nausea, bone pain, hair loss, decreased appetite, dizziness, liver damage, and skin changes.

So, what food is the safest option for vitamin A?

Common 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.

Actually, plants are rich in carotenoids, which protect our vision.

Milk and egg contain smaller amounts of preformed vitamin A as well.

Sources:

  1. NCBI – Bookshelf – Vitamin A Toxicity
  2. NCBI – Pubmeb.gov – The acute and chronic toxic effects of vitamin A.
  3. NCBI – Pubmeb.gov – Vitamin A and Retinoids as Mitochondrial Toxicants
  4. NCBI – Pubmeb.gov – Evaluation of vitamin A toxicity.
  5. NCBI – Pubmeb.gov – Retinol and retinyl esters: biochemistry and physiology Thematic Review Series: Fat-Soluble Vitamins: Vitamin A
  6. National Institutes of Health (NIH) – Vitamin A Fact Sheet for Health Professionals
  7. NCBI – Pubmeb.gov – β-Carotene Is an Important Vitamin A Source for Humans