Health Effects
Vitamins are essential for the normal growth and development of a multicellular organism. It requires certain vitamins and minerals to be present at certain times. These nutrients facilitate the chemical reactions that produce among other things, skin, bone, and muscle.
If there is serious deficiency in one or more of these nutrients, a child may develop a deficiency disease. For example, microorganisms in the intestine — commonly known as “gut flora” — produce vitamin K and biotin, while one form of vitamin D is synthesized in the skin with the help of the natural ultraviolet wavelength of sunlight. Examples include vitamin A, produced from beta carotene, and niacin, from the amino acid tryptophan.
[8] Once growth and development are completed, vitamins remain essential nutrients for the healthy maintenance of the cells, tissues, and organs that make up a multicellular organism; they also enable a multicellular life form to efficiently use chemical energy provided by food it eats, and to help process the proteins, carbohydrates, and fats required for respiration.
Biological Significance Of Vitamins
Some of the first evidence for the existence of vitamins emerged in the late 19th century with the work of Dutch physician and pathologist Christiaan Eijkman. In 1890 a nerve disease (polyneuritis) broke out among his laboratory chickens.
In 1897 he demonstrated that polyneuritis was caused by feeding the chickens a diet of polished white rice but that it disappeared when the animals were fed unpolished rice. In 1906–07 British biochemist Sir Frederick Gowland Hopkins observed that animals cannot synthesize certain amino acids and concluded that macronutrients and salts could not by themselves support growth. Funk proposed that the polyneuritis arose because of a lack in the birds’ diet of a vital factor (now known to be thiamin) that could be found in rice bran.
Because each of these factors had a nitrogen-containing component known as an amine, he called the compounds “vital amines,” a term that he later shortened to “vitamines.” The final e was dropped later when it was discovered that not all of the vitamins contain nitrogen and, therefore, not all are amines.
Discovery And Original Designation
Some of the first evidence for the existence of vitamins emerged in the late 19th century with the work of Dutch physician and pathologist Christiaan Eijkman. In 1890 a nerve disease (polyneuritis) broke out among his laboratory chickens.
In 1906–07 British biochemist Sir Frederick Gowland Hopkins observed that animals cannot synthesize certain amino acids and concluded that macronutrients and salts could not by themselves support growth. In 1912—the same year that Hopkins published his findings about the missing nutrients, which he described as “accessory” factors or substances—a Polish scientist, Casimir Funk, demonstrated that polyneuritis produced in pigeons fed on polished rice could be cured by supplementing the birds’ diet with a concentrate made from rice bran, a component of the outer husk that was removed from rice during polishing. Funk proposed that the polyneuritis arose because of a lack in the birds’ diet of a vital factor (now known to be thiamin) that could be found in rice bran.
Because each of these factors had a nitrogen-containing component known as an amine, he called the compounds “vital amines,” a term that he later shortened to “vitamines.” The final e was dropped later when it was discovered that not all of the vitamins contain nitrogen and, therefore, not all are amines.
Vitamin A Deficiency
In humans, one of the earliest signs of vitamin A deficiency is night blindness (nyctalopia), the visual failure to adapt promptly from light to darkness and to see in the dark. This aspect of vision is normally dependent on rhodopsin, which maintains its photosensitivity only in the presence of vitamin A.
If the deficiency is severe and persists, especially in malnourished infants and children, a condition known as xerophthalmia may develop. The mucous surfaces of the eye may become eroded in spots, allowing infection to set in, thus leading to ulceration and other destructive changes of the cornea (the transparent outer covering of the eye) and other eye structures. This condition will eventually result in blindness.
Except in the later stages, when cellular damage in the cornea and associated deeper structures is too extensive, xerophthalmia can be effectively treated with vitamin A. The global incidence has been estimated at some 500,000 new cases per year, half of which lead to blindness. In order to prevent xeropthalmia, infants in some countries are given a single large dose of vitamin A at six months of age, followed by another dose four to six months later.
The defective mucous surfaces have weakened resistance to bacterial invasion, and their susceptibility to various infections increases. If insufficient intake of vitamin A is prolonged, the skin may become dry and rough, with the appearance of plugs of horny material about the hair follicles (follicular hyperkeratosis).