Vitamin A is taken up via the food we eat. Animal-derived products including liver, milk and eggs contain vitamin A as retinol, whereas plant-derived foods including fruits, vegetables and nuts provide carotene, a precursor of vitamin A.
What are the functions of vitamin A?Vitamin A supports health and wellbeing by regulating different cellular processes throughout the body:
Vitamin A preserves the eyesight: Vitamin A protects against age-related macular degeneration, night blindness, keratitis and dryness of the eyes.
Vitamin A strengthens the immune system: Vitamin A prevents infections such as cold and flu, and fights inflammations.
Vitamin A supports the protective function of the skin by keeping it healthy: Vitamin A is a key component for building and maintaining epithelial tissue and mucosa.
Vitamin A prevents cellular ageing: Vitamin A regulates cell division and differentiation on several levels. Vitamin A also contributes to the apoptosis (cell death) of cancer cells.
Causes and symptoms of vitamin A deficiency
Vitamin A is absorbed from food. Malnutrition therefore is a frequently observed cause for Vitamin A deficiency, particularly in developing countries.
Vitamin A deficiency can also be caused by insufficient absorption and utilisation of fats via the mucous membranes. This can be associated with disorders including gluten intolerance, leaky gut syndrome, irritable bowel syndrome, or cystic fibrosis.
Typical symptoms of vitamin A deficiency include:
- Visual disturbances
- Night blindness
- Abnormalities of the conjunctiva
- Dryness of the eyes
- Thickening of the cornea
- Respiratory disorders
- Increased susceptibility to infections
- Alterations of the skin or mucosa
How much Vitamin A is needed?
The concentration of Vitamin A is indicated in retinol equivalents (RAE) as a common denominator of the different forms of vitamin A. The recommended daily allowance (RDA) of vitamin A is determined by age:
Average RDA in microgram (µg) RAE*:
- Children under 13 - 400 - 600 µg RAE (1333 IU - 2666 IU)
- Adolescents and adults - 900 µg RAE für Männer (3000 IU) and 700 µg RAE for women (2333 IU)
- Pregnancy - 750 - 800 µg RAE (2500 IU - 2666 IU)
- Lactation - 1200 - 1300 µg RAE (4000 IU - 4333 IU)
Who should take vitamin A?
Vitamin A is an essential vitamin for basic cellular functions, and is therefore required daily. People with higher vitamin A requirements, for example in the presence of mucosal disease, or during pregnancy and lactation associated with malnutrition, need to increase their daily uptake of vitamin A. 
Vitamin A for healthy vision and macular degeneration
Light particles hitting the retina are triggering signals to the brain, where these are converted to form a picture. Rhodopsin is a visual pigment component of the rods within the retina. These are responsible for light-dark vision.
Vitamin A is an essential building block to make rhodopsin. A vitamin A deficiency causes a shortage of rhodopsin, thereby reducing the eye’s capacity to adjust to different shades of brightness. Eventually this insufficiency advances to night blindness.
During the course of age-related macular degeneration, the vision in the middle of the retina, called the macula, deteriorates. The macula is responsible for focussing in the center of the field of vision. In the advanced stage of disease, objects are becoming blurred and can only be perceived at the periphery of the field of vision. Macular degeneration can further progress to blindness. Vitamin A can slow down progression of macular degeneration.
Vitamin A for healthy skin
The skin continuously undergoes renewal, in order to respond to environmental impact and to heal. The skin requires vitamin A to optimally support functions of the uppermost layer of the skin. Vitamin A works internally as well as applied externally. Vitamin A is crucial for healthy, protective skin. Vitamin A helps to fight acne and can contribute to the prevention of skin cancer.
Vitamin A for an effective immune system
Vitamin A is key to an effective immune response to fight invading germs. Vitamin A orchestrates different groups of cells of the immune system, boosting the immune response. Vitamin A plays a major role in the local immune response of the mucosa.
In children, vitamin A’s contribution to the immune system can dampen the effect of potentially lethal infections.
Vitamin A is also considered an antioxidant, neutralising free radicals in the body. The antioxidant effect of vitamin A also reduces cellular over-reactivity. This specific function of vitamin A can reduce cellular responses during inflammation, and can protect against developing allergies caused by chronic inflammation. 
Vitamin A and cell renewal
Vitamin A appears to be involved in the renewal and differentiation of virtually every cell in the body. Vitamin A is critical for activation and cell division of intestinal epithelial cells, as well as of bone and cartilage tissue. Vitamin A is also involved in the specification of sperm cells. However, vitamin A does not necessarily exert activating functions - it also contributes to the apoptosis of cancer cells.  
Vitamin A during pregnancy and lactation
Due to its role in cell division and tissue development, vitamin A is critically involved during pregnancy and lactation. Vitamin A deficiencies during this time can have fatal consequences for both mother and child. Caution is advised when administering vitamin A however, as over-treatment can also be potentially harmful for the unborn child. 
How does vitamin A differ from beta carotene?
Beta carotene is a pro-vitamin that needs to be converted into the bioactive component before use. This conversion takes place in the body after ingestion.
Vitamin A, also called retinol, is contained in animal derived foods including liver or dairy products. Beta carotene belongs to the biochemical family of carotenes. These are found in plants.
Vitamin A derived from animal products is therefore directly bioavailable, while plant-derived vitamin A needs to be converted before use. Both forms of vitamin A fulfil the same cellular functions though.
Vitamin A and beta carotene in foodstuffs
Vitamin A is found in all animal products. Products including liver, salmon, eel, egg yolk, dairy products and butter are especially high in vitamin A.
Products containing high amounts of beta carotene include green leafy vegetables such as broccoli, spinach, peas, cabbage, as well as orange and yellow fruits and vegetables including sweetcorn, sweet potatoes, carrots, pumpkin, blood grapefruits, oranges, melons, cherries, and papaya. 
Vitamin A side effects
Uptake of excessive amounts of vitamin A can have side effects. This is of particular importance during pregnancy, when both vitamin A deficiency and excess can have detrimental effects on the child.
Excessively high amounts of vitamin A can also lead to intoxication. It is noteworthy, however, that intoxication can only occur when taking vitamin A, not by ingestion of the plant-derived provitamin beta carotene. 
Vitamin A interactions
Some medications can affect the absorption of vitamin A. The over the counter weight loss supplement orlistat reduces the absorption of fat in the intestine. It thereby also blocks the uptake of vitamin A, potentially contributing to a vitamin A deficiency.
Several prescription medications for the treatment of skin diseases such as psoriasis are based on synthetically produced retinoids. In combination with vitamin A supplements, these can contribute to hypervitaminosis (vitamin A intoxication).
Careful study of the package leaflet is therefore strongly recommended during concomitant use of vitamin A supplements and medications.
Vitamin A Studies and references
- National Institutes of Health Vitamin A
- Dr. Padam Pande Vitamin A deficiency Symptoms, Causes and Treatment
- Cruz S, da Cruz SP, Ramalho A. Impact of Vitamin A Supplementation on Pregnant Women and on Women Who Have Just Given Birth: A Systematic Review. J Am Coll Nutr. 2017 Oct 31:1-8.
- Grune T, Lietz G, Palou A, et al. β-Carotene Is an Important Vitamin A Source for Humans. J Nutr. 2010;140(12):2268S-2285S.
- Alov, I.A. Cell division and vitamin A. Bull Exp Biol Med (1957) 43: 206.
- Ross AC, Gardner EM. The function of vitamin A in cellular growth and differentiation, and its roles during pregnancy and lactation. Adv Exp Med Biol. 1994;352:187-200.
- Beijer MR, Kraal G, den Haan JM. Vitamin A and dendritic cell differentiation. Immunology. 2014 May;142(1):39-45.
- Nagao A. Oxidative conversion of carotenoids to retinoids and other products. J Nutr. 2004 Jan;134(1):237S-240S.
- de Oliveira MR. Vitamin A and Retinoids as Mitochondrial Toxicants. Oxid Med Cell Longev. 2015;2015:140267.
- Rössner S, Sjöström L, Noack R. Weight loss, weight maintenance, and improved cardiovascular risk factors after 2 years treatment with orlistat for obesity. European Orlistat Obesity Study Group. Obes Res. 2000 Jan;8(1):49-61.
- Rollman O, Vahlquist A. Psoriasis and vitamin A. Plasma transport and skin content of retinol, dehydroretinol and carotenoids in adult patients versus healthy controls. Arch Dermatol Res. 1985;278(1):17-24.