Vitamin A

July 21, 2020

What is vitamin A?

Vitamin A, also known as retinol, is a fat-soluble vitamin which is naturally found in many foods. The body needs vitamin A for healthy vision, reproduction and the immune system. It is an essential micronutrient, meaning the body is unable to make its own vitamin A, so must get it from the diet.

Why take a vitamin A blood test?

A vitamin A blood test measures how much retinol is in the blood. The test is used to diagnose vitamin A deficiency in people who are displaying possible symptoms. There are certain diseases which can also impair the absorption of vitamin A and the test may help to identify them, too.[1]

You can check your level of vitamin A together with 50 other biomarkers integral to good health within Forth’s Ultimate blood test.

​What function does vitamin A have in the body?

Vitamin A has a variety of roles in many physiological processes in the body, including:

  • Maintaining the function and integrity of surface tissues like the skin and the linings of the respiratory tract, gut and the eye
  • Daily replacement of dead skin cells
  • Helping vision in poor visibility such as during the night
  • Growth and developing
  • Maintaining the good health status of the immune system
  • Reproduction

There are two main sources of vitamin A, plant and animal sources. In animal sources, vitamin A is in its active form, retinol. While, in plant sources, vitamin A is in the form, carotenoids, which must be converted into retinol before the body can use it. Carotenoids are responsible for the red and orange colours in fruit.[2]

​How do changes in vitamin A affect health and wellbeing?

Vitamin A provides support to many systems in the body and having too much or too little in the body can negatively affect our health. Vitamin A deficiency is rare in the UK and is often a result of malnutrition. Deficiency is more common in developing countries where the diet may be limited. The symptoms of vitamin A deficiency often affect surface tissues and linings.

Equally, vitamin A toxicity can also be harmful and occurs when too much of the micronutrient is ingested, especially in individuals who use supplements. [3]

If you are worried about your vitamin A level or just want to check where you fall on the range, you can test your vitamin A with Forth’s leading blood test service.


What can cause vitamin A to change?

Vitamin A deficiency is usually caused by malnutrition or malabsorption disorders like coeliac disease, cystic fibrosis or chronic pancreatitis. The elderly are also at risk of deficiency, as are alcoholics and individuals with liver disease.

Toxicity, on the other hand, is usually caused by over-supplementation. However, it can also occur when eating vitamin A rich food, particularly liver.

What are the most common symptoms of high or low vitamin A?

One of the first symptoms to occur in vitamin A deficiency is poor vision. Other symptoms include:

  • Dry, irritated eyes
  • Dry hair, skin, mouth
  • Loss of tears
  • Fatigue
  • Diarrhoea
  • Bladder infections
  • Respiratory infections
  • Poor wound healing[4]

The symptoms of vitamin A toxicity are:

  • Blurred vision
  • Nausea
  • Bone pain
  • Reduced appetite
  • Dizziness
  • Swelling

How to keep vitamin A in the healthy range

You should be able to ensure a healthy intake of vitamin A by consuming a healthy, balanced diet which incorporates some vitamin A rich sources. If you do this, there should be no need to supplement your intake which will help to reduce the risk of toxicity.

There are two sources of vitamin A, plant and animal.

Plant sources include:

  • carrots
  • cantaloupe melon
  • tomatoes
  • mango
  • sweet potato
  • red peppers
  • peas
  • spinach

Animal sources are:

  • liver
  • egg yolk
  • milk
  • fish

Try not to overcook these sources, if possible, as this can decrease their nutrient content including vitamin A. If you are pregnant you should speak with your GP about how much vitamin A you need and which sources you should be getting it from.

Exercise is vital for a healthy lifestyle, too. Everyone should aim to complete at least 150 minutes of aerobic every week and this should be completed over a period of five days. Aerobic exercise includes activities like walking, jogging, swimming and cycling. Exercise is also widely beneficial for the normal function of our gut. Physical activity benefits the gut environment as well as the diversity of gut microbes.[5] Therefore, exercise is important for our health and can aid the normal functioning of the body, including the digestive system.

- Health scores calculated



[1] Lab Tests Online UK. (2017). Vitamin A. Available at:

[2] Gilbert, C. (2013). What is Vitamin A and Why Do We Need It? Community Eye Health Journal: 26(84), p65.

[3] Lab Tests Online UK. (2017). Vitamin A. Available at:

[4] North London Obesity Surgery Service. (2018). About Vitamin A and Vitamin A Deficiency. Available at:

[5] Clarke, S, F., Murphy, E, F and O’Sullivan, O et al. (2014). Exercise and Associated Dietary Extremes Impact on Gut Microbial Diversity. Gut: 63, pp 1913-1920.

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This information has been medically reviewed by Dr Nicky Keay

Nicola has extensive clinical and research experience in the fields of endocrinology and sport and exercise medicine. Nicky is a member of the Royal College of Physicians, Honorary Fellow in the Department of Sport and Exercise Sciences at Durham University and former Research Fellow at St. Thomas' Hospital.

Dr Nicky Keay

Dr Nicky Keay

BA, MA (Cantab), MB, BChir, MRCP.