Vitamin A

What is Vitamin A?

Vitamin A is a fat-soluble vitamin and consists of unsaturated organic compounds known as retinol, retinal, retinoic acid and provitamin A carotenoids. It has many important functions which includes growth and development, maintaining the immune system and providing good vision. The retina of the eye requires Vitamin A in the form of retinal which makes it important for good vision.

Health Benefits of Vitamin A

Essential for good vision
Plays an important role in healthy bone growth
Helps with tooth enamel
Essential for reproduction
Plays a role in cell division and cell growth
Maintains a healthy immune system
Supports growth of healthy skin

Agonist / Synergists

Vitamins: B1, B2, B3, B6, B12, C, E
Minerals: Ca, K, Mg, Mn, P, Se, Zn

Fat

Zinc is required for vitamin A transport, absorption and metabolism. Zinc is an important cofactor needed to convert retinol to retinal. Deficiency of zinc can impair utilization of vitamin A. [https://www.ncbi.nlm.nih.gov/pubmed/9701158] [https://www.ncbi.nlm.nih.gov/pubmed/6786155]

Antagonist

Vitamins: D, E (large doses)
Minerals: Ca, Cu, Na, Se

Fibre

Food Sources of Vitamin A

Cheese
Milk
Yoghurt
Eggs
Oily fish
Foods fortified with Vitamin A
Liver and liver products such as liver pate

You can also get vitamin A by including in your diet fruits and vegetables rich in beta-carotene. The body can convert beta-carotene into Vitamin A.

Food sources of beta-carotene include yellow, red and green (leafy) vegetables, such as spinach squash, peas, carrots, sweet potatoes and red peppers broccoli. Beta-carotene can also be found in fruits such as cantaloupe, mango, papaya and apricots.

Recommended Dietary Allowance

The amounts recommended for vitamins and minerals are different for each country which can be found on the government website of host country. The nutritional data for each country are based on scientific research which are presented by the scientific academies in each country to help advise governmental departments for food and human nutrition.

Below is a list of some of the countries and the EU for which nutritional guidelines are available found on corresponding official government website (including the national academy of science website for the USA).

Vitamin A Supplementation

It is easy to get adequate amounts of Vitamin A from a diet with food sources of Vitamin A. Supplements may be recommended by your doctor if you have severe vitamin A deficiencies due to digestive disorders causing malabsorption of nutrients or are on a very poor diet.

Deficiency Symptoms of Vitamin A

People most likely to have Vitamin A deficiency are those with diseases digestive disorders and disorders that affect the way food is absorbed, which includes coeliac disease, crohn’s disease and giardiasis. Other diseases such as cystic fibrosis and diseases of the liver or pancreas can affect absorbing Vitamin A. Excess alcohol consumption can also greatly deplete vitamin A levels.

Vitamin A deficiency can cause the following symptoms

Infections, including throat and chest infections
Impaired immune function
Gastroenteritis
Delayed growth and bone development in children and teenagers.
Miscarriage
Infertility
Dry skin, dry hair, and itching
Poor vision in the dark (night blindness)
Keratomalacia (drying and clouding of the cornea)
Xerophthalmia (dryness of the conjunctiva and cornea)
Bitot's spots (oval, triangular or irregular patches on the white of the eyes)
Severe sight impairment
Perforation of the cornea

Toxicity Symptoms of Vitamin A

Vitamin A is a fat-soluble vitamin. Any vitamins that are fat soluble taken in through the diet can take longer to be excreted by the body than water soluble vitamins. Although researches have successfully created water soluble Vitamin A these are up to 10 times more toxic than the fat soluble Vitamin A.

These toxicities only occur with preformed (retinoid) vitamin A found in vitamin A animal foods such as liver, dairy and oily fish.

Toxicity can occur in with excessive consumption of alcohol which can stress the liver. Toxicity can also occur in people with renal failure.

Studies have shown that high intake of Vitamin A has been linked to decreased bone formation which may be because Vitamins A and D compete for the same receptor to interact with parathyroid hormone. This helps to regulate calcium levels. Very high levels of Vitamin A suppresses bone building while simultaneously stimulating bone breakdown. This is especially a major risk for people already suffering from osteoporosis and other bone disorders.

High levels of vitamin D may be protective against the bone density lowering effects of high vitamin A, whereas insufficient or very low levels of vitamin D may lower bone density due to the presence of high levels of Vitamin A.

Vitamin A is also very toxic in high amounts for pregnant women and can harm an unborn baby.

There have been studies where consumption of alcohol paired with high dose Vitamin A and beta-carotene supplementation played a role in causing hepatic injury (a liver injury).

Liver is a very rich source of vitamin A, if you are eating this more than once a week you may be risking intakes of high levels of Vitamin A, which can be particularly harmful to pregnant women.

People with a stressed liver especially from excess alcohol consumption may be more susceptible to vitamin A toxicity.

Some of the symptoms of vitamin A toxicity include:

Nausea
Irritability
Reduced Appetite
Anorexia
Vomiting,
Blurry vision
Headaches
Hair loss
Muscle and abdominal pain
Weakness
Drowsiness
Altered mental state

More severe toxicity symptoms of Vitamin A include:

Dry skin
Drying of the mucous membranes
Fever
Hair loss
Insomnia
Fatigue
Anaemia
Weight loss
Diarrhoea
Bone fractures

Beta-carotene which is found mostly in fruits and vegetables do not produce these symptoms unless a person has problems with chronic alcoholism. Excessive dietary intake of beta-carotene can lead to carotenodermia, which is a harmless condition but can be unappealing as it causes a yellow or orange discoloration of the skin.