Nutrients in Foods - Vitamins

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Nutrition Information

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Vitamins: Vital Dietary Components

By definition, vitamins are essential organic (carbon-containing) substances needed in small amounts in the diet for normal function, growth, and maintenance of the body.  Although vitamins themselves yield no energy to the body, they often participate in energy-yielding reactions.  Vitamins A, D, E, and K are fat soluble, whereas the B vitamins and vitamin C are water soluble. In addition, the B vitamins and vitamin K function as parts of coenzymes (that is , compounds that help enzymes function).  

The Fat-Soluble Vitamins - A, D, E, and K

Vitamins A, D, E, and K are absorbed along with dietary fat.  These vitamins travel with dietary fats through the bloodstream to reach body cells.  Special carriers in the bloodstream help distribute some of these vitamins.  Fat-soluble vitamins are stored mostly in the liver and fatty tissues.  

When fat absorption is efficient, about 40% to 90% of the fat-soluble vitamins are absorbed.  Anything that interferes with normal digestion and absorption of fats also interferes with fat-soluble vitamin absorption.  People who use mineral oil as a laxative at mealtimes risk fat-soluble vitamin deficiencies because the intestine does not absorb mineral oil.  Fat-soluble vitamins are simply eliminated with the mineral oil in the feces.  

Vitamin A

Vitamin A is found in foods in a variety of forms.  Retinol is one example.  As a family, the various forms are called preformed vitamin A or retinoids.  Vitamin A activity in the diet also occurs in the form of common plant pigments - carotenoids - such as the yellow-orange, betacarotene pigment in carrots.  Carotenoids are also called provitamin A because parts can often be turned into vitamin A.  Over 600 carotenoids are found in nature; about 50 of them serve as provitamin A.  The most potent form of provitamin A is betacarotene.  The preformed vitamin A and the provitamin A carotenoids both make up what is generically referred to as vitamin A.

Vitamin A performs many important functions in the body.  Its importance to vision s perhaps its best-known role and the only role clearly understood.  Vitamin A performs important functions in light-dark and colour vision.  It is a  key part of the visual cycle.  For a person to see in dim light, one form of vitamin A is required to start the chemical process that signals the brain that light is striking the eye.  This allows the eye to adjust from bright to dim light (such as after seeing the headlights of an oncoming car).  Without sufficient dietary vitamin A, eventually the eye cannot quickly readjust to dim light.  The condition is known as night blindness.  An injection of vitamin A into the bloodstream can cure night blindness in matter of minutes!

If night blindness is not corrected and vitamin A deficiency progresses, the cells that line the cornea of the eye ( the clear window of the eye) also lose their ability to produce mucus.  The eye then becomes dry.  Eventually, when dirt particles scratch the dry surface of the eye, bacteria infect it. The infection soon spreads to the entire surface of the eye and leads to blindness.  This disease process is called xerophthalmia, which means dry eye.

A recent study also suggests that deterioration of the retina more likely takes place when a person's diet is low in certain carotenoids (e.g., lutein and zeaxanthin) over an extended period of time.  

Vitamin D

Vitamin D is not just a vitamin.  It is also considered a hormone because cells in the skin can convert a cholesterol-like substance to vitamin D, using sunlight.  These skin cells are different from those cells that respond mostly to vitamin D, namely bone cells and kidney cells.  

The main function of the vitamin D hormone (called calcitriol) - produced by this two-step process - is to help regulate calcium and bone metabolism.  In concert with other hormones, especially parathyroid hormone (PTH), vitamin D closely regulates blood calcium to supply appropriate amounts of it to all cells.  This task entails a variety of processes: the vitamin D hormone helps regulate absorption of calcium and phosphorus from the intestine, it reduces kidney excretion of calcium, and it helps regulate the deposition of calcium in the bones.  

Even tissues in the brain, pancreas, and pituitary gland appear to be influenced by the vitamin D hormone.  More interestingly, vitamin D is capable of influencing development in some cancer cells, such as skin, bone, and breast cancer cells.  Indeed, adequate, vitamin D status has been linked to reduced risk for developing breast, colon, and prostate cancer.  Recent studies have also shown that the vitamin D hormone controls the growth of the parathyroid gland, aids in the function of the immune system, and contributes to insulin secretion and sin cell development.  The latter reason is why a form of vitamin D is used in topical preparation help treat the skin disorder psoriasis.  

Vitamin E

Vitamin E has been called the "vitamin a in search of a deficiency disease."  However, growing evidence suggests that an inadequate intake increases the risk for heart disease and cancer.  

Vitamin E can help improve vitamin A absorption if the dietary intake of vitamin A is low. In addition, vitamin E is used to metabolize iron in the cell and help maintain nervous tissue, immune, and insulin function.  

A deficiency of vitamin E causes cell membrane breakdown, especially in red blood cells of premature infants.  Unsaturated fatty acids in the red blood cell membrane are very sensitive to attack by oxidizing compounds.  Because vitamin E neutralizes these agents, it protects the red blood cell membrane from damage.  Red blood cell breakage, called hemolysis, commonly occurs in premature infants because they did not receive sufficient vitamin E from their mothers.  The rapid growth of premature infants, coupled with the high oxygen concentration found in infant incubators, greatly increases the stress on red blood cells.  This raises the risk of cell damage.  Special formulas and supplements designed for premature infants can help compensate of lack of vitamin E.  

Vitamin K 

Vitamin K is vital for blood clotting.  The K stands for koagulation as it is spelled in Denmark.  This spelling is used because a Danish researcher first noted the relationship between vitamin K and blood clotting.  Vitamin K contributes to the synthesis of several blood-clotting factors, including prothrombin.  

A newborn's intestinal tract lacks sufficient vitamin K- producing bacteria to allow for blood to clot effectively if the infant is injured.  Therefore vitamin K infections are routinely given shortly after birth to bridge the gap until enough bacteria are present to synthesize the vitamin K needed by the infant.  In adults, deficiencies of vitamin K have occurred when a person takes antibiotics for a long period and in the presence of severe long-standing fat malabsorption.  Long-term antibiotic use most likely leads to this problem because it destroys many of the intestinal bacteria that normally account for some of the vitamin K absorbed.  

 

The Water-soluble Vitamins - The B Vitamins and Vitamin C

Water-soluble vitamins are more readily excreted than fat-soluble vitamins. Any excess generally ends up in the urine or stool, so consuming the water-soluble vitamins regularly is important.  Because they dissolve in water, large amounts of these vitamins can be lost during food processing and preparation.  

The B Vitamins

The B vitamins are thiamin, riboflavin, niacin, pantothenic acid, biotin, vitamin B-6, folate, and vitamin B-12.  Because they often occur in the same foods, a lack of one B vitamin may mean other B vitamins are also low.  The B vitamins are all changed into coenzymes, small molecules that can interact with enzymes to enable enzymes to function.  In essence, the coenzymes contribute to enzyme activity.  

The B vitamins play many key roles in metabolism.  The metabolic pathways used by carbohydrates, fats, and amino acids together require input from B vitamins in their coenzyme forms.  This makes many B vitamins interdependent because they participate in the same processes.  

Thiamin

Thiamin (formerly called vitamin B-1) is used, among other purposes, to release energy from carbohydrate.  Its coenzyme participates in reactions in which a carbon dioxide (CO2) is lost from a larger molecule.  This reaction is particularly important in metabolizing glucose, the primary nutrient yielded from carbohydrate digestion.  

The thiamin deficiency disease is called beriberi, a word that means "I can't, I can't" in the Sri Lankan language of Sinhalese.  The symptoms include weakness, loss of appetite, irritability, nervous tingling throughout the body, poor arm and leg coordination and deep muscle pain the calves.  A person with beriberi often develops an enlarged heart and sometimes severe edema (wet beriberi).  

Riboflavin

the name riboflavin comes from its yellow colour (flavus means yellow in Latin).  Riboflavin was formerly referred to as vitamin B-2.  

The coenzymes of riboflavin participate in many energy-yielding metabolic pathways.  When cells form cellular energy using oxygen-requiring pathways, such as when fats are broken down and burned for energy, the coenzymes of riboflavin are used.  Some vitamin and mineral metabolism also requires riboflavin.  In addition, because of its link to activity of certain enzymes, riboflavin is believed to have a antioxidant role in the body.  

The symptoms associated with riboflavin deficiency include inflammation of the mouth and tongue, dermatitis, cracking of tissue around the corners of the mouth (called cheilosis), various eye disorders, sensitivity to the sun, and confusion.  the first symptoms of a deficiency are inflammation of the mouth and tongue.  All symptoms associated with deficiency develop after approximately 2 month on a riboflavin-poor diet (containing one fourth or less of the RDA).  

Niacin

Niacin is actually composed of a pair of related compounds.  Both can function as niacin in the body. Niacin was formerly referred to as vitamin B-3.  

The coenzyme forms of niacin function in many cellular metabolic pathways.  In general, when cell energy is being formed, a niacin coenzyme is used.  Synthetic pathways in the cell - those that make new compounds - also often use a niacin coenzyme.  This is especially true for fat synthesis.  

Because almost every cellular metabolic pathway uses a niacin coenzyme, a deficiency causes widespread changes in the body  The entire group of symptoms is known as pellagra, which means rough or painful skin.  The symptoms of the disease are known as the three Ds-dementia, diarrhea, and dermatitis (especially on areas of skin exposed to the sun).  Later death often results.  Early symptoms include poor appetite, weight loss, and weakness.

Pantothenic Acid

Like the other B vitamins, pantothenic acid helps release energy from carbohydrates, fats, and protein. By forming its coenzyme, called coenzyme A, pantothenic acid allows many important energy-yielding metabolic reactions to occur.  Coenzyme A makes other molecules much more reactive.  For example, coenzyme A must activate fatty acids before they can break down to yield energy.  It is also used in the beginning steps of fatty acid synthesis.  

Biotin

Biotin exists in two active forms in foods.  In the ultimate coenzyme form, biotin acts in fat and carbohydrate metabolism.;  Specifically, biotin assists the addition of carbon dioxide to other compounds.  By doing so, it promotes the synthesis of glucose, fatty acids, and DNA, while helping to break down certain amino acids.  Symptoms of biotin deficiency include a scaly inflammation of the skin, changes in the tongue and lips, decreased appetite, nausea, vomiting, a form of anemia, depression muscle pain and weakness, and poor growth.  

Vitamin B-6

Vitamin B-6 is actually a family of three compounds.  All can be changed to the active vitamin B-6 coenzyme.  The general vitamin name is pyridoxine.

The coenzymes of vitamin B-6 are needed for the activity of numerous enzymes involved in carbohydrate, protein, and fat metabolism.  Because vitamin B-6y is needed in so many areas of metabolism, a deficiency results in widespread symptoms, such depression, vomiting, skin disorders, irritation of the nerves, and impaired immune response.  

The most important function of vitamin B-6 concerns protein because metabolizing any amino acid requires the vitamin B-6 coenzyme.  By helping to split the nitrogen group (-NH2) from an amino acid the coenzyme participates in reactions that allow a cell to synthesize nonessential (dispensable) amino acids.  

Another important role of vitamin B-6 is to reduce an important cause of heart disease.   Scientists estimate that about 10% of heart disease in the United States results from excess homocysteine in the blood.  Vitamin B-6 is needed to recycle this compound back to a common food constituent, the amino acid methionine.  

Folate

In the past, folate was referred to as folic acid and folacin.  Today the term folate is preferred because it encompasses the variety of food forms of the vitamin.  

A key role of the folate coenzymes is helping to form DNA.  The active coenzymes help in this synthesis by supplying or accepting single carbon compounds.  The coenzymes also help metabolize various amino acids and their derivatives.  

One major result of a folate deficiency is that in the early phases of red blood cell synthesis the immature cells cannot divide because they cannot form new DNA.  When fewer mature red blood cells are present, the blood's capacity to carry oxygen decreases, causing a form of anemia.  In short, a folate deficiency causes megaloblastic anemia.  

Vitamin B-12

Vitamin B-12 represents a familh of compounds that contain the mineral cobalt. All vitamin B-2 compounds are synthesized by bacteria, fungi, and other lower organisma.  

Vitain B-12 participates in a variety of cellular reactions.  Probably its most important function is in folate metabolism.   Vitamin B-12 is required to convertr folate coenzymes to the active forms needed for iimportant metabolic reactions, such as DNA sysnthesis,.  Without vitamin B-12, reactions that require certaain active forms of folate do not take place in the cell.  Thus a vitamin B-12 deficiency contributes to a folate deficiency.  Another vital function of vitamin B-12 is maintaining the myelin sheaths that insulate nerve fibers fromn each other.  People with vitamin B-12 deficiencies show patchy destruction of the myelin sheaths.  This destruction eventually causes paralysis and perhaps death.  

Infants who are breastfed by vegertarian or vegan mothers are at risk for vitamin B-12 deficiency accompanied by anemia and long-term nervous system problems, such as diminished brain growth, degeneration of the spinal cord, and poor intellectual development.  The problems may have their origins during pregnancy, when the mother is deficient in vitamin B-12.  Vegan diets supply little vitamin B-12 unless they include vitamin B-12 - enriched food or supplements.  

Vitamin C

The best understood function of vitamin C is its role in synthesizing the protein collagen.  This protein is highly concentrated in connective tissue, bone, teeth, tendons, and blood vessels.  It is very important for wound healing.  Vitamin C increases the cross-connections between amino acids in collagen, greatly strengthening the tissues it helps form.  

Scurvy, the vitamin C deficiency disease, was long ago a constant threat to the health of sailors.  Its symptoms include weakness, opening of previously healed wounds, slower wound healing times, bone pain, fractures, bleeding gums, diarrhea, and pinpoint hemorrhages around hair follicles on the back of the arms and legs.  A vitamin C deficiency can cause widespread changes in tissue metabolism.  Most symptoms of scurvy are linked to a decrease in collagen synthesis.  About 20 to 40 days with no vitamin C intake are required for the first symptoms of scurvy to appear.  

Vitamin C is vital for the function of the immune system, especially for the activity of certain cells in the immune system. Thus disease states can increase the need for vitamin C, although we don't know what amount above the RDA is needed (if any).  Partly on the basis of this observation , Dr. Linus Pauling gained great notoriety by claiming that vitamin C could combat the common cold.  he claimed that 1000 milligrams (1gram) or more of vitamin C daily could reduce the number of colds for most people by nearly half. As a result of the popularity of his books and the respectability of his scientific credentials, millions of Americans supplement their diets with vitamin C.   

Vitamin-Like Compounds

A variety of vitamin-like compounds are found in the body.  These include the following: inositol, choline, carnitine, taurine, lipoic acid.  All these vitamin-like compounds are necessary to mnaintain proper metabolism in the body,  They can be synthesized by cells using common building blocks, such as amino acids and glucose.  In disease states, synthesis of vitamin-like compounds may not meet needs, so dietary intake can be crucial.  

(The nutrition information is referred to Contemporary Nutrition by Gordon M. Wardlaw, third edition, 1997)

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