Nutrition Basics: Vitamin A

Posted on by Matthew Wong Sang

Why do we need it?

Vitamin A is crucial for maintaining good eye health. It is needed for proper ocular (eye) function and prevention of xerophthalmia -the medical term used to refer to the ocular manifestations or conditions (such as night blindness), which occur as a consequence of vitamin A deficiency (VAD). VAD is the main cause of preventable blindness worldwide. Apart from vision, vitamin A also plays important roles in the following:

  • Reproductive health
  • Embryonic growth and development
  • Strengthening of the immune system
  • Development and maintenance of epithelial cells (these are cells that line the surfaces of your body such as the skin)
  • Development of normal teeth and hair
  • Bone development
  • It has a protective effect on the skin and mucosa (the moist tissue that lines certain parts of the inside of your body like the nose, mouth and digestive tract)

How can we get it?

There are two main sources of vitamin A: preformed vitamin A and provitamin A carotenoids (carotenoids are colourful plant pigments).

Preformed vitamin A (from animal sources)

This form of vitamin A exists primarily as retinol or retinyl ester. It is found in foods of animals origin such as:

  • Dairy products
  • Egg yolk
  • Human milk
  • Fish oils
  • Liver
  • Fortified foods
  • Supplements (predominantly retinyl acetate or palmitate)

Provitamin A Carotenoids (from plant sources)

Beta-carotene, alpha carotene, and beta-cryptoxanthin are the major provitamin A carotenoids. These are found in foods of plant origin such as:

  • Dark-green leafy vegetables (e.g. kale, spinach)
  • Yellow and orange vegetables (e.g. carrots, pumpkin, sweet potato, butternut squash)
  • Yellow and orange fruits ( e.g. papaya, mango, apricots, oranges)
  • Red palm oil
  • Fortified foods
  • Supplements ( typically beta carotene)

Carotenoids are converted to retinol in the body.

How much do we need?

The table below summarizes the vitamin A requirements for adults:

Don’t take the numbers and the varying estimates too seriously. At the end of the day, they are only meant to be general references at the population level. In reality, absorption will vary from person to person.

Note: Although pregnant women have increased vitamin A requirements, excessive intake should be avoided as it can lead to possible teratogenic effects ( i.e. abnormalities/ birth defects).

This line marks the end of all that you really need to know… Feel free to read on though!

Absorption

Vitamin A is a fat-soluble vitamin, it should therefore come as no surprise that dietary fat has a positive effect on the absorption of both preformed vitamin A and provitamin A carotenoids. About 70-90% of the preformed vitamin A consumed, is absorbed and utilized or stored. Unfortunately, this is not the case for provitamin A carotenoids which have a much wider range of efficacy due to its more complex absorption process. This is something to keep in mind if you have a predominantly plant-based diet (like me!). The good news is that the body can downregulate the bioconversion of provitamin A carotenoids, so a high intake of these plants foods is not something to be particularly concerned about.

Storage

The liver is the main storage site for vitamin A. Excess preformed vitamin A can be stored in the intestine, kidney and lastly, adipose tissue. The aforementioned downregulation of carotenoid bioconversion is controlled by the vitamin A levels in the liver.

Note: Since vitamin A can be stored, it is okay to get more on some days and less on others.

Further reading

If you are a doctor, scientist, someone with a biology/chemistry background, or just a crazy nerd like me and you want to understand vitamin A more deeply, check out the references below which will provide significantly more detail into the biological processes involved. Additionally, there is research (some of it on-going) investigating topics such as: the interactions between vitamin A and other nutrients like protein, iodine, zinc and iron; the role of vitamin A in obesity, and the role of vitamin A in the regulation of fat reserves. But that’s only a handful! Just like most of the nutrition field, there is a vitamin A rabbit hole just waiting for you to dive into!

References

Here are the main references that I used in writing this post:

If you’d like to read other online articles/blog posts like this, check out:

(Yes… I did just link my competition! Haha)

If you found this post informative, then please help to spread the knowledge by sharing it! đŸ™‚

Disclaimer: Please note the date of publish or last update on all posts. All content on 100yearsthedream.com, regardless of date, is solely for informational purposes only. All content, including images, videos and external sources, is not intended as a substitute for professional medical advice, diagnosis or treatment. Consult your own doctor/healthcare professional before adopting any suggestions or ideas shared on this website.