talking about vitamin A, the first thing we mention probably is the relevant deficiency disease. But recently, experts
begin to worry that whether too much amount of this vitamin will become a
poison. Scientific results tell us that ordinary diet will not lead to it.
Lacking of vitamin A is one of the four deficiency
diseases in the world. This vitamin is a necessary organic compound for normal
vital activities. Its amount in the human body is quite tiny. But it plays a
very important role in metabolism and growth.
four functions of this type of vitamin. The first is to maintain the
integrality of mucous layer. Or it will lead to keratosis. The second function is to compose the photoactive substances in
the visual cells. Otherwise, the adaptation of the eyes would be worse. And
sometimes patients would even suffer from nyctotphlosis.
Another function is to promote the growth and procreation. And the last is to
of vitamin A in the world can lead to a death of one million to 2.5 million. A
half million children under the school age would become blind every year
because of this reason. A four-month-long investigation about it in China revealed that 11.7% of children in China lacked
this vitamin. This problem in China,
especially the western China,
is quite severe. In developed countries, clinical cases are much fewer but the
situation is also worrying.
we should keep in mind that vitamin is water-soluble or fat-soluble. When there
is too much in the human body, the water-soluble vitamin will not affect the
body but the fat-soluble vitamin will be stored in the fat and become a
poison. Vitamin A belongs to the
fat-soluble type, storing in the liver. Excessive vitamin A can cause
diet and nutrient fortified food
generally would not lead to poisoning. Almost all the poisoning is eating too
much by accident. As early as the 1590s, pathfinders in the arctic pole ate the
liver of polar bears, which contained a large amount of vitamin A, had the
symptoms o headache, vomit and somnolence. Once a 19-year-old man ate
half a kilo of dog livers and was poisoned by vitamin A. Later, he was advised
not to livers for half a year. Too much amount will destroy the cells and
bones. So if excessive vitamin A is ingested by pregnant women, it will even
lead to congenital malformation.