Vitamin A:The vision vitamin

Vitamin A:The vision vitamin

Vitamin A is an essential micronutrient. The human body does not produce it and therefore it must be included in our diet. Also, vitamin A is a fat-soluble vitamin which is stored in our body and dissolves in fat. All the sources of vitamin A need some fat in the diet to aid absorption. It exists naturally in the food we eat and can also be consumed through supplements. In this article we will shed light on vitamin A, its forms, food sources, benefits, recommended daily intake, as well as problems relating to its deficiency and toxicity.

Forms and Food sources

Two forms of vitamin A are available in the human diet: preformed vitamin A (retinol and its esterified form, retinyl ester) and provitamin A carotenoids. Liver, including fish liver, is the richest food source of preformed vitamin A. Considerable amounts are also found in fish oils, egg yolk (not the white), meat, poultry and dairy products, whereas the second type, provitamin A, is found in fruit and vegetables. This includes carrots, yellow and dark green leafy vegetables (e.g spinach, broccoli), pumpkin, apricots and melon. Other good sources of vitamin A are red palm oil and biruti palm oil. It is worth noting here that if these oils are boiled to remove their colour, the vitamin A is destroyed. It is important that all sources of vitamin A are not overcooked, as this can affect the vitamin A content. In addition, exposure to ultraviolet light can reduce the percentage of vitamin A content in food, and consequently, it is advisable not to dry fruit that content vitamin A under direct sunlight.

By far, the most important provitamin A carotenoid is beta-carotene. Other provitamin A carotenoids are alpha-carotene and beta-cryptoxanthin. The human body converts these plant pigments into vitamin A. Both provitamin A and preformed vitamin A must be metabolized intracellularly to retinal and retinoic acid, the two active forms of vitamin A. These active forms need retinol-binding protein to store the vitamin in the liver until it is required by the body and is bound to protein before being transported to where it is needed. Other carotenoids found in food, such as beta-carotene, are inactive forms of vitamin A, so they are not converted into vitamin A.

Importance

Now what is the importance of vitamin A to our body? Vitamin A is usually related to vision and is needed to maintain eyesight and protect it from night blindness and age-related decline, but it also has multitasked. For example, it improves the immune system, helps with fat storage and protects against infections. It is also needed to grow new cells, lower cholesterol levels and reduce the risk of heart disease. Vitamin A helps in the formation and maintenance of skin, hair, eyes, as well as in bone and teeth growth. It promotes healthy growth and reproduction, reduces your risk of acne. It may also lower the risk of certain types of cancer. Additionally, vitamin A helps maintain surface tissues such as your skin, intestines, lungs, bladder and inner ear.

Recommended vitamin A daily intake

The amount of vitamin A that we need daily depends on our age and sex. The total vitamin A content in a food is usually measured as micrograms ( ) of retinol equivalents (RE). The recommended amount of vitamin A to people aged 19 to 64 need is 700  a day for males and 600  a day for females. Because children are constantly growing, they need a relatively higher intake of vitamin A, about half as much as that needed by an adult. Any excess of consumed vitamin A will be automatically stored to cover possible future low intake.

Vitamin A deficiency

Deficiency, or hypovitaminosis A is the lack of vitamin A in your blood and tissues. This is due to either insufficient amounts of vitamin A in our diet, or reduced absorption, storage or transport of vitamin A. Over time, the lack of vitamin A means that we may develop problems with our eyesight such as poor vision in the dark (night blindness) and be more prone to infections, including throat and chest infections. Other risks also include gastroenteritis, delayed growth and bone development both in children and teenagers, infertility, miscarriage, and both skin and hair problems.

Vitamin A toxicity

Here a question arises: what happens if we have too much amount of vitamin A in our body? The answer is that this would result in hypervitaminosis A, or vitamin A toxicity, which can be either an acute or a chronic condition. Acute hypervitaminosis A occurs when a person consumes large quantities of vitamin A over the course of few hours. By contrast, chronic hypervitaminosis A occurs when vitamin A levels build up slowly in the body over time. The most common side effects of chronic vitamin A toxicity, often referred to as hypervitaminosis A, includes:

  • Vision disturbances
  • Joint and bone pain.
  • Poor appetite
  • Hair loss
  • Headache
  • Confusion
  • Sunlight sensitivity
  • Dry skin
  • Itchy skin
  • Liver damage
  • Jaundice
  • Delayed growth

Acute vitamin A toxicity is associated with more severe symptoms, including liver damage, increased intracranial pressure and even death.

 

In conclusion, it is highly advisable to consume fresh food sources of Vitamin A rather than food supplements in adequate amounts in order to profit from its vital benefits and to avoid risks related to its deficiency and toxicity.

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