Tuesday, October 3, 2023

Vitamin A: A complete guide

Everything you needed to know about vitamin A, its health benefits, dosages, sources, and other important concerns.

Executive Summary

Vitamin A helps in vision, immunity, skin health, and reproduction. It is useful in night vision, age-related macular degeneration, certain types of cancers, severe acne, psoriasis, wrinkles, dry skin, sunburns, etc. It helps a couple in preparing for pregnancy as well as the baby’s growth during pregnancy.

Animal food sources such as organ meats, eggs, and dairy give vitamin A directly. Plant sources such as carrots and tomatoes give carotenoids, which are indirect forms of vitamin A.

Toxic levels of vitamin A are just 3-4 times the recommended daily levels. You run a risk of vitamin A toxicity if you consume direct vitamin A supplements or organ meats.

Carotenoids and their supplements are the safest sources of vitamin A. Supplements of carotenoids are six times more effective than those available in foods. Aim for 1,000 µg RAE a day.

Read the article for more details.

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Vitamin A is good for your eyes‘ and ‘carrots give vitamin A‘, we learned these in our school days. But there is much more to vitamin A than just eye health. There are many more complexities involved in getting vitamin A from foods. In this article, I will discuss this important nutrient.

What is Vitamin A?

Vitamin A is a group of fat-soluble compounds that have similar structures and act in many body functions. The ones that our body uses are called retinal and retinoic acid. The form in which vitamin A is stored in our body is called retinyl esters. And the compounds we get through foods that are eventually converted into usable forms of vitamin A are retinol and beta-carotenes.

Enjoying all these names? There are more to come.🤓 And if you are not enjoying them at all, don’t worry. You don’t need to remember them.

Functions of Vitamin A

Vitamin A is involved in many body functions such as vision, immunity, skin health, and reproduction.


Vitamin A forms a light-sensitive protein called rhodopsin in the retina. This compound helps convert light energy to electrical signals that are sensed by cells in the eye and conveyed to the brain as images. Rhodopsin mainly helps in low-light conditions. As a result, the first sign of vitamin A deficiency is poor vision in low- or night-lights. Going further, the time taken by the eyes to adjust to low light increases. Finally, night blindness can result.

Vitamin A also helps form a protein called iodopsin in the retina. This chemical is helpful for seeing colours. Lack of vitamin A can cause colour blindness, though this is a rare problem.

General Knowledge

For billions of years, proteins formed from vitamin A helped small organisms harvest light energy. Slowly, as organisms grew in size, their skins or outer membranes containing such photoreceptor proteins developed the ability to sense light. That became refined over millennia to the current forms of eyes and vision.

Since this ability developed in each species independently over so many years, different lifeforms excel at visual acuity to varying levels: Eagles and goats have far sharper eyesight than humans. Owls and cats see very well at night in dim light. And sea urchins and hydras have no eyes at all but can sense the light through their bodies using the same chemicals mentioned above.

You can say that vitamin A-based light-sensing ability developed at different speeds in various species depending on their habitat and survival needs.

Vitamin A supports the functioning of the cornea as well as the conjunctiva membrane. These are the outer layers of the eye. Vitamin A deficiency leads to dryness in the conjunctiva, causing dry and rough linings of the eyelid. The dried cornea becomes cloudy and scarred. Eventually, blindness sets in.


Most people think that the role of our immune system is to attack and destroy the enemies of the body. But for a healthy immune system, it needs to do two other tasks:

  1. Not attack the own body or its parts (self- or auto-immunity); and
  2. Not attack the external agents that harmless or useful to the body (e.g., healthy bacteria in the intestines).

Vitamin A helps in all these three aspects of immunity. Keep this in mind if you are suffering from an auto-immune condition. Read: Vitamin A Signals Offer Clues To Treating Autoimmunity.

Skin and Mucous Barriers

Vitamin A maintains the barrier functions of the skin and mucosal barriers.

Vitamin A helps keep skin moisturised. It also prevents cracking or breakups in the skin. If there is a wound, vitamin A speeds up healing. Vitamin A deficiency can lead to small bumps at the base of the hair on the skin causing sandpaper-like skin.

Various mucous membranes of the nose, sinuses, mouth, inner ears, lungs, intestines, urinary tract, bladder, and vaginal lining are kept healthy by vitamin A. In vitamin A deficiency, the urinary tract and vaginal lining may get dry and inflamed causing a burning sensation as well as bleeding.

Cell Functioning

Vitamin A is needed for cells to grow and duplicate correctly. That helps proper formation as well as maintenance of vital organs such as the eyes, lungs, and heart.

Reproductive System

Since Vitamin A helps in cell duplication, it is required for the growth of an embryo and fetus. It also helps in the male and female reproductive health.

Sources of Vitamin A

Vitamin A cannot be synthesized by the body. It must be obtained from the foods we eat. Our diet contains two sources of vitamin A:

  1. Preformed vitamin A; and
  2. Provitamin A carotenoids.

Preformed vitamin A

This form is as it says—performed. It is the ready-to-use form of vitamin A. It is found in animal foods such as organ meats, fish, eggs, and dairy products.

One needs to be careful with this source because if one eats enough of it, especially liver meats, one can end up with vitamin A toxicity. More on that later.

Provitamin A

Provitamin means a substance that is converted into a vitamin within an organism. Provitamin A is thus the precursor that needs to be converted to vitamin A in the body. Provitamin A comes in three forms:

  1. Alpha-carotenes;
  2. Beta-carotenes; and
  3. Beta-cryptoxanthins.

Didn’t I tell you there are more long names to come? Anyway, despair not. Just remember the beta-carotenes. The other two are similar to them but about half as potent.

These three compounds are called carotenoids, which are plant pigments. They give lovely yellow, orange and red colours to vegetables. There are a thousand other carotenoids. But for our vitamin A needs, only these 3 carotenoids matter.

The food sources of provitamin A are yellow, orange, and green leafy fruits and vegetables.

Incidentally, there are three other carotenoids that matter in eye health, viz., lutein, lycopene, and zeaxanthin. But they have nothing to do with vitamin A. Neither can they be converted to vitamin A nor are their actions similar to vitamin A’s.

Daily Requirements of Vitamin A

The recommended dietary allowance or RDA of vitamin A is 900 µg and 700 µg for men and women, respectively.

Since the body needs to convert carotenoids into vitamin A before using them, 1 µg of carotenoids is not the same as 1 µg of vitamin A. In fact, even the different carotenoids differ in their potency. To avoid this complication, the convention is to talk about the vitamin A contents of any source in term of, well, the net vitamin A you will get from it. This is termed Retinol Activity Equivalent or RAE.

One microgram vitamin A is obviously one microgram RAE. So the RDAs of vitamin A are specified as 900 µg RAE and 700 µg RAE for men and women, respectively. In summary:

  • 1 µg retinol = 1 µg RAE
  • 1 µg preformed vitamin A = 1 µg RAE
  • 12 µg dietary beta-carotene = 1 µg RAE
  • 24 µg dietary alpha-carotene or dietary beta-cryptoxanthin = 1 µg RAE

Interestingly, for dietary carotenoids (those that are obtained from plants) to be absorbed in the intestines, they must be released from the food matrix (fiber, et cetera) and mixed into fats and bile. Cooking helps release them. Also, some amount of fat is needed in the meal to mix with them. Keep that in mind, if you think you can eat a raw carrot and get a lot of vitamin A.

Instead, carotenoid supplements have them removed from the plant fiber matrix and mixed with oils. Supplemental carotenoids have nearly six times more absorption rate in the intestines than dietary carotenoids.

  • 2 µg supplemental beta-carotene = 1 µg RAE; as against
  • 12 µg dietary beta-carotene = 1 µg RAE.

This means that if you want to take beta-carotenes from your carrots, oranges, and tomatoes, you will need nearly six times more beta-carotene in them than if you were to take a beta-carotene supplement.

Upper Limit on Vitamin A Intake

For most nutrients, the toxic levels of their intake are hundreds of times more than their recommended intake levels. However, vitamin A is a nutrient whose upper limit is 3000 µg a day, which is just three to four times its daily recommended intake. So it is easy to slip into toxicity if one were to take vitamin A supplements or even eat organ meats regularly. A short video on this:

A simple solution to this is to take the vitamin A requirements through carotenoids. Since the body needs to convert them into vitamin A before using them, the toxic levels are never reached. The body just does not convert more than its required needs.

Carotenoids, on the other hand, are not toxic even in large excess levels. At the most, you run a risk of turning orange like a rabbit bunny.🐇 And that too temporarily, till you stop your carrot consumption. A short video:

Benefits of Vitamin A Supplementation

Many benefits of vitamin A such as those for vision and immunity are well known. The benefits for skin problems and cancer are seen in some but not all clinical trials. A few other benefits in autoimmune conditions such as inflammatory bowel disease and psoriasis are claimed but so far, they have not been proven clinically.

I suggest that you discuss with your doctor and consider supplementation of carotenoids (not vitamin A) if you face any of these conditions. Evaluate the pros versus the cons of the decision to supplement.

Eye Health

Read: Vitamin A is beneficial for the eyes.

Cancer Protection

Vitamin A supplements may reduce the risk for certain types of cancers, such as skin, bladder, lung, and breast cancer. There are two reasons for this:

  1. Vitamin A helps in cell development and error-free duplication. That reduces chances of cancerous growth;
  2. Vitamin A increases the activity of immune cells. Such cells are able to identify and destroy cancerous cells, stopping cancer developement at a very early stage.

Read: Vitamin A, Cancer Treatment and Prevention. Kindly don’t exclusively rely on vitamin A for any cancer management. You must take your doctor’s treatment for cancer. You can discuss vitamin A supplementation with your doctor and if she approves of it, consider taking carotene supplements.

If you want to reduce the risk of getting cancer, there is no harm in taking carotene supplements since they also help the body with other benefits.

Skin Disorders

  • Since vitamin A helps skin protect its barrier functions, it is useful for severe acne and psoriasis;
  • Can protect from premature skin ageing by sun exposure;
  • Can reduce fine lines and wrinkles. It is a good antioxidant and can prevent skin oxidative stress, which causes breakdown of collagen and elastin, the skin proteins.

Read: Vitamin A and Skin Health.

Reproductive Health

  • Helps in embryonic, fetal, and placental growth as vitamin A is needed for cell growth and duplication;
  • Helps in sperm development;
  • Since vitamin A maintains mucosal linings, it helps in keeping male genital tract healthy;

Pregnant women as well as couples trying for a child should consider vitamin A supplementation. Read: Vitamin A in Reproduction and Development.

Other Uses

As mentioned earlier, there is very little research on the last three benefits. You take a call on how to proceed with them: “What is the harm?” versus “Why do trial and error?” argument.

To Read More

  1. National Institutes of Health: Vitamin A and Carotenoids: Fact Sheet for Health Professionals
  2. National institutes of Health: Vitamin A: Fact Sheet for Consumers
  3. Healthline: Vitamin A: Benefits, Deficiency, Toxicity, and More
  4. Linus Pauling Institute, Oregon State University: α-Carotene, β-Carotene, β-Cryptoxanthin, Lycopene, Lutein, and Zeaxanthin
  5. University of Rochester Medical Center: Vitamin A

Articles in Nutrients Series

  1. Omega–3 Oils: A Complete Guide
  2. Vitamin D: A Complete Guide
  3. Vitamin A: A Complete Guide
  4. Coenzyme Q10: A Complete Guide
  5. Turmeric (Curcumin): A Complete Guide
  6. Lutein: A Complete Guide

Articles in Supplementation Series

  1. Why Do We Need Supplements?
  2. Supplements for Various Age Groups
  3. Supplements for Preventing Ageing & Age-Related Diseases
  4. Supplements for Type 2 Diabetes
  5. Supplements for Osteoarthritis
  6. Supplements for Hair Loss
  7. Supplements for Fatty Liver
  8. Supplements for Autoimmune Disorders
  9. Supplements for Anemia
  10. Supplements for Prostate Enlargement
  11. Supplements for Macular Degeneration
  12. Supplements for PCOS
  13. Supplements for Parkinson’s Disease
  14. Supplements for Gout
  15. Supplements for Eczema

First published on: 3rd May 2022
Image credit: Food leaf photo created by timolina – www.freepik.com
Last updated on: 24th June 2022


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