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The water-soluble vitamins
This group contains the B vitamins and vitamin C. They received their names from the labels B and C on the test tubes in which they were first discovered. It was later discovered that the test tube containing the B vitamins had more than one vitamin in it., which were then named vitamin B1, B2 etc.
The eight B vitamins play an important role in assisting enzymes in carbohydrate, fat, and protein metabolism and in the making of DNA and new cells.
Thiamin (Vitamin B1)
Requirements
The RDA for thiamin is 0,5 mg/1000 kcal per day. This is about 1 mg per day, assuming an average daily dietary intake is about 2000 kcal/p. A balanced diet should provide sufficient thiamin. People who take a lot of their energy from sugar or alcohol may get thiamin deficiency. People who fast or who are dieting have to ensure that they get the same amount of thiamin as when on a 2000 kcalory diet.
Best sources
Pork and ham are very good sources for thiamin, as well as yeast, liver, whole grains, nuts sunflower seeds, peas, watermelon, oysters, oatmeal and wheat germ.
Functions
Thiamin is a part of TPP, a coenzyme necessary for energy metabolism. The nervous system and muscles are dependent on thiamin.
Deficiency symptoms
Beriberi can result from a long-term thiamin deficiency. This disease was first discovered in the Far East when the custom of polished rice, removing the thiamin-rich hulls, became widespread. Beriberi leads to nervous system damage and muscle wasting. Other deficiency symptoms are abnormal heart rhythms, heart failure, weakness, difficulties in walking, mental confusion, and paralysis.
Toxicity
An abnormally high intake of thiamin affects the nervous system. It causes hypersensitivity reactions, which can lead to weakness, headaches, irritability and insomnia. The blood system can be affected, causing a rapid pulse.
Riboflavin (Vitamin B2)
Requirements
The RDA for riboflavin is 0,6 mg/ 1000 kcal per day. That is about 1,2 mg per day. Children and pregnant women require additional riboflavin because it is necessary for growth.
Best sources
Milk and milk products, such as cheese, and good sources of riboflavin. Therefore, it is important to include them in the daily diet. Most green vegetables and grains contain riboflavin; broccoli, asparagus and spinach are good sources.
Functions
Like thiamin, riboflavin serves as a coenzyme; it helps enzymes to release energy from nutrients essential for the human body. Riboflavin plays an important role during the final stage of metabolism of the energy nutrients.
Deficiency symptoms
No disease is associated with riboflavin deficiency. Lack of riboflavin can cause symptoms such as skin rash, cracks and redness near the corners of the eyes and lips, as well as a hypersensitivity to light (photophobia). It can also cause cracks at corners of the mouth (cheilosis).
Toxicity
There are no known toxicity symptoms of riboflavin.
Did you know?
Light and irradiation can destroy riboflavin. This is why milk is seldom sold in transparent glass. On the other hand, riboflavin is heat stable, so cooking usually does not destroy it. It is also used as food additive, E101.
Niacin (Vitamin B3)
Requirements
The RDA for niacin is 6.6 mg NE (niacin equivalents) /1000 kcal, or 13 mg, per day. A NE is the amount of niacin that is present in food, including the niacin that can theoretically be made from its precursor tryptophan. 60 mg of tryptophan can deliver 1 mg of niacin.
Best sources
Meat, poultry and fish are good sources of niacin, as are enriched breads and cereals. Mushrooms, asparagus and green leafy vegetables are the richest vegetable sources.
Functions
Both coenzyme forms of niacin, NAD and NADP are needed for many metabolic activities, particularly the metabolism of glucose, fat, and alcohol. Niacin is unique among the B vitamins in that the body can build it from the amino acid tryptophan. Niacin supports the health of skin, nervous system, and digestive system.
Deficiency symptoms
Pellagra, a niacin deficiency disease, leads to symptoms such as dermatitis, diarrhoea, and dementia. It was widespread in the US South in the early 1900s.
Further deficiency symptoms are loss of appetite, weakness, dizziness, and mental confusion. The skin can show symptoms of bilateral symmetrical dermatitis, especially on areas that are exposed to sunlight.
Toxicity
High amounts of niacin act as drugs on the nervous system, on blood lipids and on blood glucose. Symptoms such as vomiting, swollen tongue, and fainting can occur. Furthermore, it can influence the function of the liver and lead to low blood pressure.
Vitamin B6 (Pyridoxine, pyridoxal, pyridoxamine)
Requirements
As vitamin B6 coenzymes play an important role in amino acid metabolism, the daily intake is proportional to the protein intake, because proteins are made up from amino acids. The RDA for vitamin B6 is 0.16mg /g protein. That means the average necessary intake is 2.0 mg/day for men and about 1.6 mg/day for women.
Best sources
Meat, fish, and poultry are the main sources of vitamin B6. Other sources are potatoes, some green vegetables and purple fruit.
Functions
Vitamin B6 is used in amino acid and fatty acid metabolism. Vitamin B6 helps the body to synthesise nonessential amino acids. It also plays a role in the production of red blood cells.
Deficiency symptoms
People whose vitamin B6 intake is too low may show symptoms such as weakness, irritability and insomnia. Further symptoms are growth failure, impaired motor function and convulsions.
Toxicity
High doses of vitamin B6 over a long period cause nerve damage, sometimes irreversible. It starts with numb feet: later, sensation may be lost in the hands and the mouth may become numb. Further toxic symptoms are difficulties in walking, fatigue, and headaches. When the intake is reduced, these symptoms diminish, but they do not always disappear completely.
Folate (Folacin, folic acid, pteroylglutamic acid)
Requirements
The RDA for folate is about 3 mg/kg body weight. For men the daily intake should be about 200 mg per day and for women about 180 mg per day. Higher levels of folate are recommended during pregnancy and whenever cells are multiplying. A deficiency can be caused not only by a low intake, but also by impaired absorption or an unusual metabolic need for the vitamin. People who consume a lot of alcohol or other empty-calory items are vulnerable. Also any conditions connected to cell multiplication, such as pregnancy, cancer, or skin-destroying diseases, such as measles, increase the need for folate.
Best sources
The best sources for folate are vegetables, especially green leafy vegetables. Liver also contains a lot of folate. Meat, milk, and milk products contain low levels of folate.
Functions
Folate is a part of two coenzymes that are essential in the synthesis of new cells.
Deficiency symptoms
Folate deficiency can lead to anaemia. The symptoms are large, immature red blood cells, indicating a slow DNA synthesis. This can be caused not only by a folate deficiency but also by a lack of vitamin B12.
Other symptoms of folate deficiency are heartburn, diarrhoea, and frequent infections due to suppression of the immune system. It affects the nervous system, leading to depression, mental confusion, fainting and fatigue.
Toxicity
Toxicity symptoms are diarrhoea, insomnia, and irritability. Because of its close relationship to vitamin B12, a high dose of folate can mask a deficiency of vitamin B12.
Vitamin B12 (Cobalamin)
Requirements
The RDA for vitamin B12 is about 2 micrograms per day.
Best sources
Vitamin B12 is almost exclusively found in animal flesh and animal products. Vegetarians can protect themselves against a deficiency by consuming extra milk, cheese, and eggs. That means about a cup of milk or one egg in a given day. Only vegans need vitamin B12 sources such as soymilk or yeast grown in a vitamin B12-enriched environment.
Functions
Vitamin B12 is important whenever cells are rapidly dividing. It also maintains the sheath that surrounds and protects nerve fibres and stimulates their normal growth. It plays a role in bone cell activity and metabolism. Vitamin B12 is also needed to free folate, so that it can help to build red blood cells.
Deficiency symptoms
Vitamin B12 deficiency can lead to anaemia, which is actually caused by folate deficiency. Without vitamin B12, folate cannot assist in the building of red blood cells. The symptoms of either deficiency are large, immature red blood cells, indicating a slow DNA synthesis. A deficiency can also affect the nervous system, leading to degeneration of peripheral nerves, progressing to paralysis. It can also cause skin hypersensitivity.
Toxicity
There are no toxicity symptoms associated with vitamin B12.
Pantothenic acid
Requirements
There is no RDA for pantothenic acid. An estimated safe and adequate intake of 4 to 7 mg per day has been established.
Best sources
Pantothenic acid is common in most food. Meat, fish, poultry, whole grain cereals and vegetables are good sources.
Functions
Pantothenic acid plays a role in metabolism as a part of coenzyme A. This coenzyme helps to carry molecules in the process of breakdown of glucose, fatty acid, and energy metabolism.
Deficiency symptoms
Deficiency symptoms are rare, and include vomiting, insomnia, and fatigue.
Toxicity
Toxicity symptoms are occasional diarrhoea and water retention.
Biotin (Vitamin B8)
Requirements
Biotin is needed in very small amounts, so there are no RDA values for it. An estimated safe and adequate daily dietary intakes is between 30 and 100 micrograms per day.
Best sources
Biotin is found in a wide range of foods. Deficiencies normally do not occur in people who consume a varied diet.
Functions
In comparison to the other B vitamins, little is known about the function of biotin as it was discovered relatively recently. It plays an important role in the metabolism of carbohydrates, fat and proteins.
Deficiency symptoms
Biotin deficiencies are rare, but can appear in hospital patients who are artificially fed. It can cause symptoms such as loss of appetite, nausea, depression, weakness, and fatigue. Extra doses of biotin are given to the patients to correct the deficiency.
Toxicity
Biotin toxicity normally does not occur.
Vitamin C
Requirements
The RDA for vitamin C is 60 mg per day, but this varies between individuals. Physical stresses such as burns, infections, toxic levels of heavy metals, cigarette smoking, the chronic use of certain medications (including aspirin, barbiturates) increase the body's need for vitamin C. Smokers need about 100 mg of vitamin C per day.
Best sources
Citrus fruits are a good source of vitamin C. Broccoli, greens, cabbage, cantaloupe and strawberries contain high levels of vitamin C. In contrast, there is very little vitamin C in milk and meat.
Functions
Vitamin C has many functions. It assists specific enzymes in performing their functions. It also works as an antioxidant. Manufacturers sometimes add it to food products to protect certain ingredients. It is also important for forming collagen, a fibrous, structural protein. Collagen is needed for bone and teeth formation and also for forming scar tissue. Vitamin C also increases resistance to infections and helps the body to absorb iron.
Deficiency symptoms
The first signs of vitamin C deficiency are bleeding around the teeth and breaking capillaries under the skin, producing pinpoint haemorrhages. A major lack of vitamin C acts on the nervous and muscular system. This can lead to muscle degeneration as well as to pain, hysteria and depression. Further symptoms are anaemia, frequent infections, a rough skin and the failure of wounds to heal.
When a person takes large amounts of vitamin C supplements over a long period, the body may adjust by destroying and excreting more of the vitamin than usual. If the intake then is reduced suddenly, the body may not stop this process, causing scurvy.
Toxicity
Symptoms of vitamin C toxicity are nausea, abdominal cramps, diarrhoea, headache, fatigue and insomnia. It can also interfere with medical tests, or cause excessive urination and the growth of kidney stones.
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Fat-Soluble Vitamins
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