Vitamin A – Benefits, Sources and Toxicity


Vitamin A

Vitamin A is fat soluble, which means it is stored in the body. It is naturally found in the tissues of plants and animals. In plant life, it occurs as carotenoids, a plant secondary metabolite that is one of the most abundant pigments found in organisms. 600 carotenoids have been discovered, with 50 of them being categorized with characteristics of Provitamin A (such as alpha-carotene, beta-carotene and beta-cryptoxanthin). It is most abundant in plant tissues that partake in photosynthesis (the green leaves of plants making them high in chlorophyll) and is in charge of the distinct colours of red, orange and yellow found on/in the skin of both plants – as well as the exoskeletons of certain fish such as salmon and carp as well as crustaceans such as lobster and shrimp – it is because these animals consume either plant matter or other animals that have themselves consumed plant matter high in carotenoids.

Carotenoids have two main actions in plant cells; protection of the cell and accessory pigments – providing colour. Some of these carotenoids have the capacity to transform into retinol in the bodies of animals. There are around 50 distinct forms compounds of carotenoids that appear in plant life; beta-carotene being the most abundant. In order for a carotenoid to be of use to an animal body, it needs to be able to split into either retinol or retinoic acid.

Skin and Mucosal Tissue
  • Stimulates growth of the base layer of skin cells as well as membranes
  • Aids in diminishing and preventing acne, as well as other inflammatory skin conditions such as psoriasis and ichthyosis.
  • Aids in maintaining the structural integrity of mucosal membranes and ensuring their proper lubrication

Vision – Night blindness
  • Night Blindness, which is also associated with diarrhea and respiratory problems is attributed to a deficiency in Vitamin A. It was in the 19th century that an association was made between a decline in nutrition and night blindness on long naval sea voyages. Although vitamin a is fat soluble it is often used up in the body if not replenished in about 6 months to a years time.
  • Vitamin A is also associated with ‘visual purple’ which allows the eyes to adjust to light and dark environments. The pigment that Vitamin A supplements in the body are Rhodopsin – and it is this pigment that is responsible for the adaptation.
  • Vitamin A is also essential for proper nerve function of the eyes – which also enables the ability of sight
Antioxidant & Immunity
  • protects the body from free radicals, neutralizes them as well as aiding in combating oxidative stress which is attributed to infections and cancer
  • The amount of Vitamin A stored in the body is a direct correlation between a risk of cancer development.
  • If there is a drastic decline or lack of vitamin A in cells within the body there is an increased potential that such cells can become malignant

Growth and Healing
  • Vitamin A, especially retinol is crucial during the baby and fetal development and growth.vitamin a is essential in the body as it is required for the laying down of new cells and well as general homeostasis.
  • Retinol and retinoic acid are both needed for reproductive health and the development of embryonic (fundamental for the appropriate development of the nervous system, skin, lungs, eyes, ears, limbs, heart, lungs, and face) reproductive organ development.
  • It is also essential for the proper formation and new bones and teeth as well as in the repair of damaged tissue.
Eggs in a basket

Food Sources of Vitamin A

It is important to understand that Vitamin A is a plant secondary metabolite – carotenoid – and its abundance in plant life, and later in animal life – will decline if the plant does not receive proper nourishment from the soil as well as time for developing.

If an animal is not provided with its natural diet, as well as a stress-free happy environment it is likely that it will not naturally be high in vitamin A – not even in the liver. Intensive livestock operations may fortify their animal feed, however, a high-stress environment may cause the gut to not work as efficiently as it should, resulting in less vitamin A being brought into the body and what is stored would be quickly used up as an antioxidant to combat oxidative stress.

Choose both plant and animal sources wisely, think local and talk with your farmer!

Vitamin A foods including both plants and animals are listed below as well as the form of vitamin A either retinol or beta-carotene that is found within it. 

Retinol/Retinoic acid

(Performed A/animal sources)

  • beef and chicken liver
  • fish oil
  • eggs
  • butter

(Pro-vitamin A/plant sources) Bright and vibrant yellow and orange fruit as well as dark green leafy vegetables – the more intense the colour the more nutrient dense the produce.

  • Carrots and Beets
  • Sweet Potatoes
  • Kale and cabbage
  • Spinach and Rapini
  • Broccoli
  • Watercress
  • Squash and pumpkin
  • Melon
  • Mangoes
  • Tomato
  • Apricots
  • Papayas
  • Tangerines
  • Asparagus

Fresh Vegetables in a basket

Vitamin A Deficiency Signs

  • inflammation and/or infection issues with eyes, ears, mouth, sinuses, lungs, urinary tract
  • infertility; particularly in women
  • If one get colds or respiratory infections easily (especially children)
  • cancer


Deficiencies may arise for a number of reasons in the body. If the intestinal tract is compromised and the enzymatic conversion of retinol in the intestines cannot occur absorption into intestinal cells will be an issue. An overgrowth of bacteria such as SIBO can also make it hard for absorption. If an individual is very low in cholesterol and chylomicrons cannot be formed properly the transportation of Vitamin A from the intestines to general circulation cannot successfully occur. This will inevitably compromise the utilization as well as storage of Vitamin A by the liver and other cells in the body.

The liver stores between 50-80% of all the body’s retinol, if it is at full capacity it can hold enough stock to supply the body for between 6 to 9 months. However, if the liver is out of balance and working sluggishly, it will not only have trouble storing vitamin A but also be utilizing it.

Being constantly stressed of very sick can lead to a decrease in Vitamin A stores. However, apart from Vitamin A many other vitamins and minerals will be lost from the body, therefore, it is best to supplement with a potent multivitamin, as well as additional vitamin C, Probiotics and herbals to strengthen the adrenals. 


There are different ways to dosage Vitamin A and it is often dependant on the form of Vitamin A as well. It is common to see International Units (IU) listed on the supplement bottle or on food labels. International Unites was the first measurement that Vitamin A went under, however, it does not provide a physical amount to how much vitamin A is truly present. IU expresses the level of chemical activity in the food or product. in the early 2000 micrograms of Retinol Equivalents (mcg REs) began being used, which provided an actual physical amount of the vitamin in question. There is a ration that will let you know the physical amount of Vitamin A if the Chemical activity is only listed: 1 mcg REs = 3.33 IU. 

Vitamin A RDA
Government of Canada Dietary Reference Intake Table for Vitamin A

The supplemental dosage maintenance dosage of Vitamin A should be around 5000IU/1500 mcg REs daily, although this is far less than the daily recommended amount, we do get a great deal of Vitamin A in the foods we eat. Moreover, as Vitamin A is fat soluble it is not often that we are deficient in it (however, if you are under high stress or you get sick often, it is definitely a vitamin that you should consider taking). If you are taking a multivitamin make sure that it provides a good source and quantity of Vitamin A. Because toxicity is easy to derive especially with oral supplementation it is important to supplement for between 4 to 6 weeks and taking a break for a week or two – a supplement holiday!

25,000 IU daily can be taken for a period of 1-2 months, no longer. You can cycle back to this amount after a period of time, which is dependant on your overall health. Higher dosages around 150,000 IU daily should be done under the direction, guidance and possible supervision of a healthcare practitioner. Vitamin A is seen and has shown to possess virus and bacteria fighting properties when taken at high doses. Elson M. Haas, MD., gives his patients a Vitamin A burst to supercharge their immune system and help them fight off infections, (this is done under physician supervision) beginning with 30,000 IU 3xdaily and working his way down over the course of a week to two weeks. Though Vitamin A can be very beneficial for the body, when supplementing at home it is a lot safer to supplement and support the immune system with Vitamin C.

Genestra Brands - A-Mulsion - Emulsified Vitamin A Liquid - Citrus Flavor - 1 fl oz (30 ml)
BlueBonnet Beta Carotene C and E Plus Selenium Vegetarian Capsules, 120 Count
Vitamin A 25,000 IU Eye and Vision Support - Retinol and Carotenoid Nutrition Made in USA 100 Tablets
Genestra Brands – A-Mulsion – Emulsified Vitamin A Liquid – Citrus Flavor – 1 fl oz (30 ml)
BlueBonnet Beta Carotene C and E Plus Selenium Vegetarian Capsules, 120 Count
Vitamin A 25,000 IU Eye and Vision Support – Retinol and Carotenoid Nutrition Made in USA 100 Tablets
Liquid Drops – Vegan Friendly
Sourced From Algae
Sourced from Fish Liver Oil
Genestra Brands - A-Mulsion - Emulsified Vitamin A Liquid - Citrus Flavor - 1 fl oz (30 ml)
Genestra Brands – A-Mulsion – Emulsified Vitamin A Liquid – Citrus Flavor – 1 fl oz (30 ml)
Liquid Drops – Vegan Friendly
BlueBonnet Beta Carotene C and E Plus Selenium Vegetarian Capsules, 120 Count
BlueBonnet Beta Carotene C and E Plus Selenium Vegetarian Capsules, 120 Count
Sourced From Algae
Vitamin A 25,000 IU Eye and Vision Support - Retinol and Carotenoid Nutrition Made in USA 100 Tablets
Vitamin A 25,000 IU Eye and Vision Support – Retinol and Carotenoid Nutrition Made in USA 100 Tablets
Sourced from Fish Liver Oil
Genestra Brand – A-Mulsion (Emulsified Vitamin A Liquid)
  • 1 drop = 10,000 IU
  • Vegan-Friendly
  • gluten-free
  • Though it is a synthesized plant-based (soy) product, the facility has very high standards of manufacturing, using pharmacological practices to manufacture natural health products. The soy is not listed as an allergen due to the fact that it is heavily refined to the point that it no longer causes harm to individuals who have soy allergies or intolerances


Bluebonnet – Beta Carotene, C, E, Plus Selenium
  • 25,000 IU from algae – Dunaliella salina
  • This supplement also includes Vitamin C (at 1000mg), Vitamin E (400 IU) and yeast free Selenium at 200 mcg to create a supercharge immune boosting formula).
  • Gluten-free, sugar-free, yeast-free


Oceanic Nutra – Vitamin A 25,000 IU
  • Made in the USA
  • Corn-free, Sugar-free, Gluten-free, Dairy-free, Soy-free
  • GMP certified facility


It is best to take a non-synthetic sourced Vitamin A (Performance or Provitamin), however, they can be hard to come by, and even with fish liver oil the quality of the fish and it’s sourcing comes into question, especially when companies do not often disclose where they derive their ingredients from. I recommend Vitamin A supplements that do not contain soy, gluten, corn, sugar or dairy. These are common allergens and are products that are often genetically modified.

When taking beta-carotene, the toxicity is not as great (however individuals who have hypothyroidism and diabetes need to be careful) because the liver needs to convert the beta-carotene into retinol in order for it to be useful in the body. If the liver is not working to par this can be difficult.

Pregnancy and Vitamin A Supplementation

Women who are pregnant or plan on getting pregnant should not exceed 3000IU (supplemented) daily as high doses of Vitamin A can lead to a risk of birth defects in the child.


Vitamin A Toxicity

Caution – as Vitamin A is fat soluble and stored in the liver it the RDA should not be exceeded during pregnancy

Signs of Toxicity;

  • headaches
  • nausea
  • vomiting
  • dizziness
  • abdominal pain/cramping
  • hair loss
  • itchy flaky skin
  • bone abnormalities
  • liver damage


Eds. Blomhoff, R. (1994). A in Health and Disease. New York; Marcel Dekker Inc.

Eds. Litwack, G. (2007). Vitamin A. New York; Elsevier.

Ganguly, J. (1989). Biochemistry of Vitamin A. Florida; CRC Press Inc.

Haas, E.M., & Levin, B. (2006). Staying Healthy with Nutrition. Celestial Arts: New York. 

Murray, M.T., & Pizzorno, J. (2012). The Encyclopedia of Natural Medicine. Atria Paperback; New York. 

Preedy, V.R. (2012). Vitamin A and Carotenoids: Chemistry, Analysis, Function and Effects. Cambridge; The Royal Society of Chemistry.

Semba, R.D. (2012). The Vitamin A Story. Lifting the Shadow of Death. New York; Karger.

Amanda Filipowicz
Amanda Filipowicz

Amanda Filipowicz is a certified nutritional practitioner (CNP) with a bachelor in environmental studies (BES) from York University. She also has certification in clinical detoxification, prenatal and postnatal care as well as nutrition for mental health. She has a decade of experience in nutritional health and is a lifelong proponent of eating healthy.

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