A General View
Until the beginning of the twentieth century, the world went on believing that fuel foods, protein, and mineral salts were the only things the body needed. Nothing was known of vitamins until about the year 1900, when certain research scientists noticed in the course of their experiments that there were obscure elements necessary to nutrition, that they contribute greatly to natural growth and the maintenance of life, and that food devoid of them causes ailments in man. Funk finally declared that these mysterious elements ought to be called "vitamins" (that is, the amines necessary for life). It later became clear that some of them dissolve in water and others in fat. To this day, scientists and nutrition experts continue their researches and investigations to discover new kinds and new benefits of these vitamins.
Vitamins play a fundamental role in the body. They are necessary
for growth, for the performance by all the organs of their functions, for reproduction and nursing, and for the maintenance of health at every age. They are important in supporting the health of the tissues and in resistance against the diseases that arise from germs.
This chapter has been devoted to treating the vitamins — their functions, their analysis, their utilization, their sources, the need for them, and the ailments their deficiency causes. To make them easier to understand, they have been classified according to whether they dissolve in water or in fat. Those that dissolve in fat are vitamins A, D, E, and K, while those that dissolve in water are vitamin C and the B complex.
The Fat-Soluble Vitamins
These vitamins are absorbed in the fat stored in abundant quantities in the body, and they are not excreted with the urine. Stored in food are many forms of substances that are not actually vitamins but are converted into them by chemical reaction inside the body.
Vitamin A
Its function: It is especially necessary for growth and for securing sight in the eye. It is also vital for the building and working of the
mucous tissues, for reproduction, and for nursing. Those who possess a sufficiency of vitamin A possess immunity against certain diseases such as the common cold. It has a close connection with the healing of wounds, for it makes them heal quickly and lessens exposure to infection by germs.
Its absorption, storage, and utilization:
Part of this vitamin found in yellow vegetables and fruits is not in fact vitamin A but a substance called carotene, which is converted into vitamin A in the liver. The true form is found in milk, eggs, and fish-liver oil. Both vitamin A and carotene are absorbed by the lymphatic vessels in the intestines. Although vitamin A is more quickly absorbed than carotene, the utilization of both takes place in the presence of fat, bile, and the secretion of the thyroid gland. Failure of the bile to be secreted, or the presence of mineral oil, or the weakness of digestive activity owing to old age, may hinder the absorption of carotene;
