Vitamin A - a comprehensive guide

Summary

Vitamin A is a fat-soluble vitamin, which means it is found primarily in fatty foods and absorbed with fats into the body. Vitamin A is actually a family of compounds that have slightly different structures, including retinol and retinoic acid. Vitamin A’s functions include supporting good vision, normal immune system function, healthy skin and mucous membranes (the ‘inner linings’ of the body), and supporting iron metabolism. ‘Real’ or ‘preformed’ vitamin A is only found in animal foods such as organ meats, eggs and dairy products. Beta-carotene, a substance that can be converted to vitamin A in the body, is found in plant foods, especially orange, red and green vegetables such as carrots.

Primary functions of Vitamin A

  • Vitamin A is important for immune function. It is said to have a role in production of white blood cells such as natural killer cells, and B lymphocytes, which produce antibodies as part of the ‘learned’ immune response.
  • Vitamin A is vital for vision. It is part of a substance called rhodopsin, a visual pigment found in the rod cells of the retina. Rhodopsin is very sensitive to light, enabling us to see in low-light conditions.
  • Vitamin A supports skin health. It is taken up by the skin cells in the dermis and epidermis, and is thought to regulate production of structural proteins such as keratin, which gives skin its strength. It may also help to protect the skin against UV damage, and is said to support collagen production for wound healing.
  • Vitamin A supports mucous membrane health too. The mucous membranes are the internal linings of the body, such as the lining of the digestive tract and the bladder. Vitamin A is said to help maintain the integrity of the mucous membranes– i.e. their barrier function, to prevent substances passing through.
  • Vitamin A supports iron metabolism. Vitamin A is thought to be needed for the body to mobilise its stores of iron so they can be used – for example in haemoglobin to carry oxygen around the body. It may also help non-heme (plant-sourced) iron to be absorbed in the gut.

Vitamin A is also said to have roles in cell differentiation, reproduction, bone growth, and formation of glycosaminoglycans (substances that form part of connective tissue), amongst others.

How much do we need?

The nutrient reference value for vitamin A is 800µg (2,666 iu). Nutrient reference values refer to the amount needed to ensure that the needs of nearly all the population (97.5%) are being met. The tolerable upper level for daily intake for adults is 3,000µg (10,000 iu).

Deficiency signs and symptoms*

More immediate deficiency signs may include the following:

  • Skin problems including rough, dry skin or acne
  • Increased infections, including throat infections
  • Poor wound healing
  • Sore or dry eyes
  • Dry hair and brittle or easily breaking nails
  • Reduced sense of taste and smell

Symptoms associated with severe deficiency may include:

  • Night blindness
  • Other eye conditions including xerophthalmia, a condition where the eyes don’t produce tears, that can lead to blindness (virtually unknown in developed countries)
  • Hyperkeratosis, a skin condition characterised thickening of the outer layer of skin
  • Bone loss.

*Note that many of these symptoms can be indications of other health conditions or deficiencies – please consult your doctor or health practitioner if you are concerned.

Forms and bioavailability

This is particularly important when it comes to vitamin A.

Beta-carotene found in vegetables and fruits is often called vitamin A, but it is not the same thing. Beta-carotene can be converted to vitamin A in the body, but this conversion rate can be very low – as little as 3 per cent! Conversion can be negatively affected by various factors, such as poor thyroid function, stress and other nutrient deficiencies. So we can get some vitamin A through beta-carotene in veggies and fruits (and beta-carotene in supplements), but it is not the body’s ideal source.

Pre-formed, or ‘real’ vitamin A refers to members of the retinoid family such as retinol as found in animal foods. In supplements, preformed vitamin A may be in the form of retinyl palmitate or retinyl acetate, which can be suitable for vegetarians and vegans. Preformed vitamin A can be used directly by the body for all its vital functions.

Food sources

The best food sources of ‘real’ vitamin A include:

  • Liver – all types! A serving of liver can contain 10,000 to 20,000iu of vitamin A. Eating a small serving (e.g. 70-80g) of liver two or three times a week is the best way to get your natural vitamin A quota. However, eating liver in excess could lead to vitamin A toxicity – and it is not advised at all for women who are pregnant or planning pregnancy.
  • Other organ meats
  • Cod liver oil. The best alternative for those who don’t like eating liver. A typical serving of cod liver oil may contain around 1,000–3,000 iu (300–900 µg) of vitamin A.
  • One egg yolk may contain around 300 iu of vitamin A.
  • Similar to egg yolks, a tablespoon of butter can contain up to 300 iu of vitamin A.
  • Fish and other meats (but much less than liver and organ meats)

Beta-carotene is found in carrots (of course!) as well as other orange vegetables and fruits, and green and red vegetables too.

Dosages

Adults: Dosages of preformed vitamin A in supplements for adults are typically between 2,500 iu (750µg) and 5,000iu (1,500µg). Levels of 10,000 iu or higher may be recommended by a practitioner for short-term therapeutic purposes in adults, but should not generally be used long-term. Beta-carotene may be used in higher doses without any risk of overdosing (the body will never convert more than it needs to vitamin A).

Children: Individual vitamin A supplements are not generally used for children other than under the guidance of a practitioner. A children’s multivitamin supplement may contain around 650–1300 iu (200–400µg) of preformed vitamin A, or more as beta-carotene.

Note: For women who are pregnant or planning pregnancy, it is advised not to take more than 2,000 iu (600 µg) of preformed vitamin A in supplement form.

What to look out for when buying a supplement

So what do you look for when buying a vitamin A supplement? Firstly, you need at least some of your vitamin A in its ‘real’ form, and not all as beta-carotene – as your body may not be able to convert a great deal of it.

The best source in supplement form is cod liver oil, which contains a completely natural form of vitamin A. However, make sure you choose a good quality product from a reputable brand, and that it actually lists vitamin A in the nutritional information.

For vegetarians or vegans – or anyone who can’t take cod liver oil – go for a supplement that contains some vitamin A in the form of retinyl palmitate or similar.

Cautions

For women who are pregnant or planning pregnancy, it is advised not to take more than 2,000 iu (600 µg) of preformed vitamin A in supplement form. Supplements that contain more than this should state on the label that the product should not be taken in these circumstances. (Beta-carotene can be taken in higher amounts, however.)

If you are taking any medications or have any medical condition, please consult your healthcare practitioner before taking vitamin A.  

 

 

       

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      Dr. Lifestyle

      Dr. Lifestyle is our own collective of leading health, nutrition and fitness experts. Having several brains makes it really hard to decide what we feel like for breakfast (Chia Coconut Pudding, or a Green Smoothie?), but when it comes to health advice we are an all-knowing, hyper-intelligent, super human.