Retinol – Vitamin A 101

Overview:

Retinol, aka preformed vitamin A, is a fat-soluble vitamin that is only found in animal-sourced foods, such as liver, oily fish, cheese, butter, heavy cream and egg yolks. Retinol plays an essential role in body growth, immune function, vision and reproductive health. It’s essential for the body to maintain homeostasis of copper. Retinol is essential to make copper bioavailable, and also to the process of recycling iron for proper hemoglobin formation.

Vitamin A comes from two sources. One group, called retinoids, comes from animal sources and includes retinol. The other group, called carotenoids, comes from plants and includes beta-carotene. The body converts beta-carotene to vitamin A. Major carotenoids, including lycopene, lutein, and zeaxantuin, have important biological properties, including antioxidant and photoprotective activities.

You can read more about the two forms of vitamin A’s differences here: 14 Differences Between Retinol and β -carotene.

Key Benefits of Retinol:

  • It helps cells reproduce normally, a process called cellular differentiation.
  • It is essential for good vision. The first sign of a vitamin A deficiency is often poor sight at night.
  • It is needed for the proper development of an embryo and fetus.
  • Immune system function
  • Healthy Body Growth
  • Bone formation
  • Reproduction
  • Wound healing
  • Retinol is vital for “loading” copper into ceruloplasmin
  • Active vitamin D must be complexed with the nuclear receptor called RXR, which requires retinol.
  • Abundant bone marrow requires lots of retinol.
  • Healthy Skin.

Key Risks of Retinol:

  • Overdosing is rarely seen and only occurs when the depots in the liver are saturated, and the intake of large amounts of vitamin A (retinol) continues.
  • Vitamin A from foods is considered safe. But you can get too much from supplements.
  • Vitamin A toxicity can occur from either the topical or oral form of Vitamin A.
  • Children are particularly sensitive to vitamin A, with daily intakes of 1500 IU/kg body weight reportedly leading to toxicity.
  • Diet – Liver is high in vitamin A. The liver of certain animals, including the polar bear, bearded seal, fish, walrus, and moose, are particularly toxic. It has been estimated that the consumption of 500 grams of polar bear liver would result in a toxic dose for a human.
  • Supplements – Dietary supplements can be toxic when taken above recommended dosages.
  • Acute toxicity occurs over a period of hours or a few days and is less of a problem than chronic toxicity.
  • Acute poisoning may occur if more than 100 milligrams of vitamin A are ingested. This is more than 100 times the RDA level of 800 micrograms (RE)
  • Chronic poisoning only occurs after several months of ingesting daily dosages of several thousand micrograms (RE).
  • Chronic toxicity results from daily intakes greater than 25,000 IU for 6 years or longer and more than 100,000 IU for 6 months or longer.
  • If ingested on an empty stomach, transient side effects such as nausea may occur.
  • The symptoms include nausea, vomiting, elevated brain pressure and headache. Also, cramps, itching, and dry and flaky skin may occur in the case of very large single doses.

What you need to know about Retinol – Vitamin A:

Retinol is highly absorbed when taken orally. When ingested, 70–90% of preformed vitamin A is absorbed and used. About 80–90% of the total body reserves of preformed vitamin A are in the liver (with 80–90% of this amount being stored in hepatic stellate cells and the remaining 10–20% being stored in hepatocytes). Fat is another significant storage site, while the lungs and kidneys may also be capable of storage.

Supplementing Vitamin D prevents the absorption of retinol, and the higher dose of D you take, the less retinol that will be available to you, thus another reason not to supplement with Vitamin D.

References:

www.hindawi.com/journals/isrn/2013/246737/

https://www.mountsinai.org/health-library/supplement/vitamin-a-retinol
https://en.wikipedia.org/wiki/Hypervitaminosis_A

The acute and chronic toxic effects of vitamin A
https://academic.oup.com/ajcn/article/83/2/191/4649798?login=false

Vitamin A Toxicity
https://www.ncbi.nlm.nih.gov/books/NBK532916/

https://www.hsph.harvard.edu/nutritionsource/vitamin-a/
https://healthandscience.eu/index.php?option=com_content&view=article&id
https://academic.oup.com/jn/article-abstract/117/9/1615/4768558?redirectedFrom=PDF

https://www.ncbi.nlm.nih.gov/pmc/articles/PMC1866639/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC299640/
https://www.ncbi.nlm.nih.gov/pmc/articles/PMC3935584/

(Mawon AR et al, 2013, Role of Fat-Soluble Vitamins A and D in the Pathogenesis of Influenza: A New Perspective. Int Scholarly Res Notices. July 19. 2012; Volume 2013 | Article ID 246737.)

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