by Marie Bywater

Created on: March 28, 2009

Vitamin A was the first vitamin discovered back in the early 1900s, and is linked to similar shaped particles known as retinoids. The most common form of Vitamin A, retinol is preformed already and is found in meat products. Retinol is a fatsoluble vitamin, so called as it requires fat for it's absorption in the gastrointestinal tract. Beta carotene is another form of vitamin A which is predominantly found in green leafy vegetables and requires conversion to active vitamin A. The majority of diets in the Western world are made up of the more bioavailable retinol whereas those in the developing countries are more saturated with the less bioavailable carotenes. Vitamin A is transported around the body bound to either retinol binding protein or another carrier protein called prealbumin for use in body tissues.

What is Vitamin A used for?

Vitamin A is a requirement for many bodily functions including excellent vision, gene transcription, immune processes, foetal development, red cell production, prevention and decreased risk of heart disease, and general reduction of the effects of damaging free radicals.

Recommended daily allowance

The RDA of this essential Vitamin differs between young and old, and male and female. Highest requirements exist for lactating females when as much as 1300 ug/day is required. Pre-school children have the lowest requirement at 300 ug/day. Modest amounts are essential for teenagers, right up to 70 year old males and females with 600-900 ug/day being the average recommended intake.

Food sources of Vitamin A

It should be extremely easy in the Western world to meet recommended requirement levels as Vitamin A is present in many foods such as meat (liver, beef, pork, chicken and fish), carrots and other vegetables including broccoli and spinach as well as in fruits such as apricot and mango. Eggs also provide a substantial amount of Vitamin A.

Deficiency

Whilst Vitamin A is plentiful in many foods there are still over 100 million children in the developing world suffering from blindness due to Vitamin A deficiency. The majority of these children are malnourished and suffering from several deficiencies and as a result have a very low life expectancy of as little as one year. The main reason for these children's Vitamin A deficiency was a diet based on rice. Vitamin A deficiency is extremely rare in the developed world but is apparent in diseases such as celiac disease due to decreases in absorption. The deficiency presents with night blindness and other vision changes such as Bitot's spots, dry eyes and cornea breakdown.

If you suspect you have Vitamin A deficiency it is important to increase your consumption of foods containing the vitamin and/ or Vitamin A supplements.

Toxicity

Vitamin A toxicity is also rare and either occurs due to excessive intake through diet or oral supplementation. Chronic toxicity is thought to occur at doses of over 25 000 IU/kg and rarely causes death. Toxicity is associated with a wide range of symptoms such as nausea, vomiting, light headedness, migraine, weight loss, brittle nails and diarrhea.

Vitamin A is essential for a range of bodily functions and is plentiful in most developed countries diets. In those cases where deficiency occurs vision losses are apparent and without treatment death may result. Toxicity also has the ability to cause death but this does not happen very often.

Learn more about this author, Marie Bywater.
Click here to send this author comments or questions.