Daily Requirements of Vitamins. A vitamin is an organiccompound needed in small quantities for normal metabolism that cannot be manufactured in the cells of the body. Lack of vitamins in the diet can cause impor-tant metabolic deficits. Table 71–3 lists the amounts of important vitamins required daily by the average person. These requirements vary considerably, depend-ing on such factors as body size, rate of growth, amount of exercise, and pregnancy.
Storage of Vitamins in the Body. Vitamins are stored to aslight extent in all cells. Some vitamins are stored to a major extent in the liver. For instance, the quantity of vitamin A stored in the liver may be sufficient to main-tain a person for 5 to 10 months without any intake of vitamin A. The quantity of vitamin D stored in the liver is usually sufficient to maintain a person for 2 to 4 months without any additional intake of vitamin D.
The storage of most water-soluble vitamins is rela-tively slight. This applies especially to most vitamin B compounds. When a person’s diet is deficient in vitamin B compounds, clinical symptoms of the deficiency can sometimes be recognized within a few days (except for vitamin B12, which can last in the liver in a bound form for a year or longer). Absence of vitamin C, another water-soluble vitamin, can cause symptoms within a few weeks and can cause death from scurvy in 20 to 30 weeks.
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