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Vitamins have a range of functions in different
animals. They regulate metabolism, help to convert carbohydrates
and fats into energy, and assist in the build of body structure,
such as formation of bones and teeth. Most vitamins of the B
complex group have coenzyme functions. Vitamins taken in excess of
the body's needs are useless; excess water-soluble vitamins are
excreted mainly in the urine. However, the excess fat-soluble
vitamins are stored in the body and could become toxic in very
large excess.
Requirements for vitamins differ during growth and
maturity, additional quantities being needed under special
circumstances such as pregnancy and lactation. The actual daily
requirements may also vary depending on inheritance, microbial
flora of the intestine, and eating habits. Thus, the recommended
daily allowances (RDAs) of vitamins may also differ from one
country to other. The standards have been set by organizations
such as FAO/WHO, MRC (Medical Research Council, UK), and NRC/NAS
(Nutritional Research Council, National Academy of Sciences, USA).
Vitamins are distributed widely in natural foods;
some foods are richer in certain vitamins and poor in others.
Vitamin deficiency rarely occurs in persons eating a wide variety
of natural foods. Green leafy vegetables, fruits, whole grain
cereals, pulses, and nuts are fairly rich sources of different
vitamins. Milk, eggs, and meat are good sources of the vitamin B
complex group, but the organ meats, such as liver and kidney, are
richer.
Vitamins are lost in various ways. Food processing
involving blanching, cooking, heating, irradiation, and removal of
water ( drying), as well as trimming and peeling, can cause
significant losses of vitamins and minerals. Most water-soluble
vitamins may be lost during cooking through leaching. Vitamins
lost during food processing may be added by fortification; the
added vitamins may be either synthetic or natural. Vitamins may
also be lost during storage of food.
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