Vitamin A (retinol)
What role does it play in the organism?
Out of its numerous functions, the best known is connected to vision. As the component of the light-sensitive pigment of the retina, it plays a central role in day and night, as well as colour vision. In addition, it is also essential for the good condition of epithelial tissues (skin, mucous membrane), and a number of other life functions (e.g. reproduction, appropriate immunity).
What foodstuffs contain it?
Good dietary sources of vitamin A are liver, egg-yolk, milk and diary products. The provitamins (substances that can be converted into a vitamin) of vitamin A are carotenoids. β-carotene is their most familiar representative. The organism is capable of converting provitamins into Vitamin A. The following fruits and vegetables are good sources of β-carotene: carrots, savoy cabbages, spinach, winter squash, apricots and cantaloupes.
Who are exposed to vitamin A deficiency and what does this deficiency state cause?
Those are exposed to it who hardly consume dairy products, liver (e.g. vegetarians) and vegetables or not at all. Severe vitamin A deficiency is rare in developed countries today, which deficiency results in night blindness, eye-dryness and keratomalacia. We need to note though that one of the most frequent reasons of childhood blindness is still vitamin A deficiency in extensive regions in Asia, Africa and South-America. According to Hungarian studies, vitamin A intake is around the requirement, so it is frequently slightly below the recommended level or just enough to cover it. Intake slightly below the required quantity causes a so-called limit-value deficiency state, which can be detected with laboratory methods only, but which does disturb life functions, even if only to a minimal extent.
What is the recommended intake for vitamin A?
The daily requirement for children ranges between 1400-3333 IU/day (=420-1000 microgram/day) depending on age and 2666-3333 IU/day (=800-1000 microgram/day) for adults.
What are the health risks of excessive vitamin A intake?
Taking more than 100000 IU a day (which is 100-125 times higher than the recommended daily allowance) for a long period of time may cause vitamin A overdose (toxicity). So, there is a slim chance for it, as it is close to impossible to take this quantity of vitamin A permanently. We need to point out two things though. One is that high vitamin A intake during pregnancy might be harmful to the baby, so the daily intake should not exceed 5000 IU during pregnancy. According to recent studies, vitamin A intake exceeding the recommended daily allowance increases the risk of osteoporosis. So, it is wise to keep to recommended daily allowances.
