Vitamin A – Benefits, Sources and Toxicity

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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. 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 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 between light and dark environments. The pigment that Vitamin A supplements in the body is 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 body from free radicals, neutralizes them as well as aiding in combating oxidative stress which are attributed to infections and cancer
  • The amount of Vitamin A stored in the body is a direct correlation for 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 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.

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 develop. 

If an animal is not provided 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!

Retinol/Retinoic acid

(Performed A / animal sources) 

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

Beta-carotene

(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

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. 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 utilizing it.

Supplementation

The dosage for Vitamin A should not exceed 600-1500 ue RE a day or 2500 – 5000 IU of retinol a day – (for both cases) minus what is in a multivitamin. These amount should be worked up towards, best with the assistance of a health practitioner. 

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 month. Do not take over 10,000 IU of retinol a day, that is the average tolerable upper intake level.

Secondly, do not touch synthetic Vitamin A or Retinol. The label of the supplement should indicate there the source of the nutrient is coming from, if it is not from a fish or other animal, or even from algae do not take it.

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.

Vitamin A Toxicity

References

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. 

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. 

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