Showing posts with label vitamins. Show all posts
Showing posts with label vitamins. Show all posts
Monday, October 24, 2011
Vitamin E and cancer
We all think of vitamin supplements as beneficial or at the very least harmless, but a study published in JAMA questions that. Men taking a vitamin E supplement for 7 years were 17% more likely than those taking a placebo to develop cancer. The difference was statistically significant. The trials was looking at whether vitamin E and selenium either together or separately could help prevent prostate cancer, and involved 35,000 healthy middle aged men. There was no impact on the incidence of other cancers, diabetes or cardiovascular events. The supplements did not save lives. Vitamin E may be natural but it is not harmless. The same, of course might be said of snakebite and the GREAT WHITE SHARK.
Tuesday, February 17, 2009
Vitamin B
The B Vitamins are a group of water-soluble substances which are not otherwise related to each other. There are eight of them, but claims for vitamin status are made for another 23. A vitamin is a substance that is essential for healthy living that cannot be synthesized by teh body. The other 23 eithercan be synthesized by teh human body or are not essential for health. I will deal with teh eight true vitamins and then explain why some of the others are not true vitamins.
Vitamin B1 or thiamine is the substance that is necessary in the diet to prevent beriberi. Chinese medical texts referred to beriberi as early as 2700 BC. Symptoms of beriberi include severe lethargy and fatigue, together with complications affecting the cardiovascular, nervous, muscular, and gastrointestinal systems. The origin of the word is from a Sinhalese phrase meaning "I cannot, I cannot", the word being doubled for emphasis. Two types of beriberi are recognized: the 'wet-type' affects the heart; through a combination of heart failure and weakening of the capillary walls, it causes the peripheral tissues to become edematous. Dry beriberi causes wasting and partial paralysis resulting from damaged peripheral nerves.
In 1884, Takaki Kanehiro, a British-trained Japanese doctor of the Japanese Navy, observed that beriberi was endemic among low-ranking crew who often ate nothing but rice, but not among crews of Western navies and officers who consumed a Western-style diet. Kanehiro initially believed that lack of protein was the chief cause of beriberi. He conducted one of the first cliical trials using the crews of two battleships; one crew was fed only white rice, while the other was fed a diet of meat, fish, barley, rice, and beans. The group that ate only white rice reported 161 crew with beriberi and 25 deaths, while the latter group had only 14 cases of beriberi and no deaths. This convinced Kanehiro and the Japanese Navy that diet was the cause of beriberi. But Kanehiro wrongly thought that protein was the missing element in the diet (Kwashiorkor, which is caused by protein deficiency also causes heart failure).
In 1897 Christian Eijkman, a military doctor in the Dutch Indies, discovered that chickens fed on a diet of cooked, polished rice developed paralysis, which could be reversed by discontinuing rice polishing (he mistakenly attributed that to a nerve poison in the endosperm of rice, from which the outer layers of the grain gave protection to the body. In 1897, Christiaan Eijkman in the Dutch East Indies, discovered that feeding unpolished rice instead of the polished variety to chickens prevented paralysis in the chickens. In 1898, Sir Frederick Hopkins postulated that some foods contained "accessory factors" — in addition to proteins, carbohydrates and fats, — that were necessary for the functions of the human body.
Eijkman was awarded a Nobel Price in Psysiology and Medicine in 1929, because his observations led to the discovery of vitamins). An associate, Gerrit Grijns, correctly interpreted the connection between excessive consumption of polished rice and beriberi in 1901: he concluded that rice contained an essential nutrient in the outer layers of the grain that was removed in polishing. In 1911 Casimir Funk isolated an antineuritic substance from rice bran that he called a “vitamine” (on account of its containing an amino group). Dutch chemists, Jansen and Donath, went on to isolate and crystallize the active agent in 1926, whose structure was determined by R.R.Williams, a US chemist, in 1934. Thiamin (“sulfur-containing vitamin”) was synthesized in 1936 by the same group. It was first named “aneurin” (for anti-neuritic vitamin).
Thiamine occurs naturally in unrefined cereals and fresh foods, particularly whole grain bread, fresh meat, legumes, green vegetables, fruit, and milk. Beriberi is therefore common in people whose diet excludes these particular types of nutrition.
Beriberi may be found in people whose diet consists mainly of polished white rice, which is very low in thiamine because the thiamine-bearing husk has been removed. It can also be seen in chronic alcoholics with an inadequate diet (Wernicke-Korsakoff syndrome), as well as being a rare side effect of gastric bypass surgery. If a baby is mainly fed on the milk of a mother who suffers from thiamine deficiency then that child may develop beriberi as well.
Wernicke’s encephalopathy (WE) is the type of thiaqmine deficiency most frequently seen in Western society. Although it may also occur in patients with impaired nutrition from other causes, it is usually seen in alcoholics. It is a striking neuro-psychiatric disorder characterized by paralysis of eye movements, abnormal stance and gait, and markedly deranged mental function.
Alcoholics may have thiamin deficiency because of the following: 1) inadequate nutritional intake: alcoholics tend to intake less than the recommended amount of thiamin. 2) decreased uptake of thiamin from the GI tract: active transport of thiamin into enterocytes is disturbed during acute alcohol exposure. 3) liver thiamin stores are reduced due to hepatic steatosis or fibrosis. 4) impaired thiamin utilization: magnesium, which is required for the binding of thiamin to thiamin-using enzymes within the cell, is also deficient due to chronic alcohol consumption. The inefficient utilization of any thiamin that does reach the cells will further exacerbate the thiamin deficiency. 5) Ethanol per se inhibits thiamin transport in the gastrointestinal system and blocks phosphorylation of thiamin to its cofactor form, TDP.
Korsakoff Psychosis is generally considered to occur with deterioration of brain function in patients initially diagnosed with WE. This is an amnestic-confabulatory syndrome characterized by retrograde and anterograde amnesia, impairment of conceptual functions, and decreased spontaneity and initiative. Because of their loss of memory they invent the most fantastic explanations for their circumstances.
However, most people on normal diets do not require vitamin B1 supplements.
Vitamin B1 or thiamine is the substance that is necessary in the diet to prevent beriberi. Chinese medical texts referred to beriberi as early as 2700 BC. Symptoms of beriberi include severe lethargy and fatigue, together with complications affecting the cardiovascular, nervous, muscular, and gastrointestinal systems. The origin of the word is from a Sinhalese phrase meaning "I cannot, I cannot", the word being doubled for emphasis. Two types of beriberi are recognized: the 'wet-type' affects the heart; through a combination of heart failure and weakening of the capillary walls, it causes the peripheral tissues to become edematous. Dry beriberi causes wasting and partial paralysis resulting from damaged peripheral nerves.
In 1884, Takaki Kanehiro, a British-trained Japanese doctor of the Japanese Navy, observed that beriberi was endemic among low-ranking crew who often ate nothing but rice, but not among crews of Western navies and officers who consumed a Western-style diet. Kanehiro initially believed that lack of protein was the chief cause of beriberi. He conducted one of the first cliical trials using the crews of two battleships; one crew was fed only white rice, while the other was fed a diet of meat, fish, barley, rice, and beans. The group that ate only white rice reported 161 crew with beriberi and 25 deaths, while the latter group had only 14 cases of beriberi and no deaths. This convinced Kanehiro and the Japanese Navy that diet was the cause of beriberi. But Kanehiro wrongly thought that protein was the missing element in the diet (Kwashiorkor, which is caused by protein deficiency also causes heart failure).
In 1897 Christian Eijkman, a military doctor in the Dutch Indies, discovered that chickens fed on a diet of cooked, polished rice developed paralysis, which could be reversed by discontinuing rice polishing (he mistakenly attributed that to a nerve poison in the endosperm of rice, from which the outer layers of the grain gave protection to the body. In 1897, Christiaan Eijkman in the Dutch East Indies, discovered that feeding unpolished rice instead of the polished variety to chickens prevented paralysis in the chickens. In 1898, Sir Frederick Hopkins postulated that some foods contained "accessory factors" — in addition to proteins, carbohydrates and fats, — that were necessary for the functions of the human body.
Eijkman was awarded a Nobel Price in Psysiology and Medicine in 1929, because his observations led to the discovery of vitamins). An associate, Gerrit Grijns, correctly interpreted the connection between excessive consumption of polished rice and beriberi in 1901: he concluded that rice contained an essential nutrient in the outer layers of the grain that was removed in polishing. In 1911 Casimir Funk isolated an antineuritic substance from rice bran that he called a “vitamine” (on account of its containing an amino group). Dutch chemists, Jansen and Donath, went on to isolate and crystallize the active agent in 1926, whose structure was determined by R.R.Williams, a US chemist, in 1934. Thiamin (“sulfur-containing vitamin”) was synthesized in 1936 by the same group. It was first named “aneurin” (for anti-neuritic vitamin).
Thiamine occurs naturally in unrefined cereals and fresh foods, particularly whole grain bread, fresh meat, legumes, green vegetables, fruit, and milk. Beriberi is therefore common in people whose diet excludes these particular types of nutrition.
Beriberi may be found in people whose diet consists mainly of polished white rice, which is very low in thiamine because the thiamine-bearing husk has been removed. It can also be seen in chronic alcoholics with an inadequate diet (Wernicke-Korsakoff syndrome), as well as being a rare side effect of gastric bypass surgery. If a baby is mainly fed on the milk of a mother who suffers from thiamine deficiency then that child may develop beriberi as well.
Wernicke’s encephalopathy (WE) is the type of thiaqmine deficiency most frequently seen in Western society. Although it may also occur in patients with impaired nutrition from other causes, it is usually seen in alcoholics. It is a striking neuro-psychiatric disorder characterized by paralysis of eye movements, abnormal stance and gait, and markedly deranged mental function.
Alcoholics may have thiamin deficiency because of the following: 1) inadequate nutritional intake: alcoholics tend to intake less than the recommended amount of thiamin. 2) decreased uptake of thiamin from the GI tract: active transport of thiamin into enterocytes is disturbed during acute alcohol exposure. 3) liver thiamin stores are reduced due to hepatic steatosis or fibrosis. 4) impaired thiamin utilization: magnesium, which is required for the binding of thiamin to thiamin-using enzymes within the cell, is also deficient due to chronic alcohol consumption. The inefficient utilization of any thiamin that does reach the cells will further exacerbate the thiamin deficiency. 5) Ethanol per se inhibits thiamin transport in the gastrointestinal system and blocks phosphorylation of thiamin to its cofactor form, TDP.
Korsakoff Psychosis is generally considered to occur with deterioration of brain function in patients initially diagnosed with WE. This is an amnestic-confabulatory syndrome characterized by retrograde and anterograde amnesia, impairment of conceptual functions, and decreased spontaneity and initiative. Because of their loss of memory they invent the most fantastic explanations for their circumstances.
However, most people on normal diets do not require vitamin B1 supplements.
Wednesday, January 14, 2009
Vitamin A
By 1906 it was known that factors other than carbohydrates, proteins and fats were necessary to keep cattle healthy. In 1917 one such substance was independently discovered by two American research groups, Elmer McCollum at the University of Wisconsin, and Lafayette Mendel and Thomas Osborne at Yale University. McCollum recognised that there were more than one of these substances and designated the fat soluble entity Vitamin A and the water soluble factor Vitamin B. In 1934 Wald isolated from animal retina a substance he called retinene. Morton in 1944 suggested that this compound was the aldehyde of vitamin A, and called it retinaldehyde (rather than retinal). The correct structure of vitamin A was deduced in 1931 by Karrer who proposed the name axerophthol (Axerophtol in German), based on its action in preventing the eye disease xerophthalmia. The first synthesis was in 1947 by two Dutch chemists, David Adriaan van Dorp and Jozef Ferdinand Arens.
Vitamin A found in foods that come from animals is called preformed vitamin A. It is absorbed in the form of retinol, one of the most usable forms of vitamin A. Sources include liver, whole milk, and some fortified food products. Retinol can be made into retinal and retinoic acid in the body. Provitamin A is found in colorful fruits and vegetables and is called carotenoid. It can be made into retinol in the body. Common provitamin A carotenoids found in foods that come from plants are beta-carotene, alpha-carotene, and beta-cryptoxanthin. Among these, beta-carotene is most efficiently made into retinol. Alpha-carotene and beta-cryptoxanthin are also converted to vitamin A, but only half as efficiently as beta-carotene.
Actually, of the 563 identified carotenoids, fewer than 10% can be made into vitamin A in the body. Some provitamin A carotenoids have been shown to function as antioxidants in laboratory studies; however, this role has not been consistently demonstrated in humans. Antioxidants protect cells from free radicals, which are potentially damaging by-products of oxygen metabolism that may contribute to the development of some chronic diseases.
Vitamin A is interesting for hematologists. The cell line HL60 is a myeloid leukemic cell line much loved by experimental hematologists. These blast-like cells can be made to differentiate into neutrophil granulocytes if exposed to vitamin A (vitamin D on the other hand turns them into monocytes) It appears that developing white cells have a receptor specifically designed for vitamin A.
Vitamin A deficiency is common in developing countries but rarely seen in the United States and Europe. Approximately 250,000 to 500,000 malnourished children in the developing world become blind each year from a deficiency of vitamin A. In Western countries, vitamin A deficiency is most often associated with strict dietary restrictions and excess alcohol intake. Strict dietary restrictions can also lead to zinc deficiency. Zinc is required to make retinol binding protein (RBP) which transports vitamin A. Therefore, a deficiency in zinc limits the body's ability to move vitamin A stores from the liver to body tissues.
Night blindness is one of the first signs of vitamin A deficiency. In ancient Egypt, it was known that night blindness could be cured by eating liver, which was later found to be a rich source of the vitamin. Vitamin A deficiency also contributes to blindness by making the surface of the eye very dry, thus it damages both the retina and the cornea.
As with other vitamins there has been interest in low storage levels of vitamin A that do not cause obvious deficiency symptoms. This supposedly mild degree of vitamin A deficiency is said to increase children's risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness. Children living at or below the poverty level, who have children with inadequate health care or immunizations, especially those from immigrant communities and those with abnormalities of fat absorption are believed to be especially at risk.
Unless a person falls into one of these groups it is entirely likely that a normal diet will provide sufficient vitamin A. Three ounces of liver, for example, provides five times the daily requirement. Vegetarians and those who do not take dairy products will have to rely on the conversion of pro-retinoids from vegetables like carrots, cabbage, spinach or broccoli.
For those who like to take megadoses of vitamins, Vitamin A is one to be wary of. Overdoses are possible and can cause birth defects, liver abnormalities, reduced bone mineral density that may result in osteoporosis, and central nervous system disorders. The pro-retinoids have also been recommended as a prophylactic against cancer. A very large study of the use of beta-carotene had to be stopped when it was found that there was a 46% increase in lung cancer in those taking beta-carotene compared with controls.
However, retinoids can be used as medicines. For about 15 years synthetic retinoids (Roaccutane® or Accutane®)) have been used to treat certain skin diseases such as acne and psoriasis, and another retinoid, all trans retinoic acid (ATRA) is used to treat acute promyelocytic leukemia. Nevertheless, even these drugs should be avoided by those likely to get pregnant, and liver function tests should be monitored.
The daily requirement for vitamin A depends on your body size, but it is about 3000 international units and the safe upper limit of intake is 10,000 international units. 10,000 international unit is equivalent to about 3000 micrograms.
Vitamin A found in foods that come from animals is called preformed vitamin A. It is absorbed in the form of retinol, one of the most usable forms of vitamin A. Sources include liver, whole milk, and some fortified food products. Retinol can be made into retinal and retinoic acid in the body. Provitamin A is found in colorful fruits and vegetables and is called carotenoid. It can be made into retinol in the body. Common provitamin A carotenoids found in foods that come from plants are beta-carotene, alpha-carotene, and beta-cryptoxanthin. Among these, beta-carotene is most efficiently made into retinol. Alpha-carotene and beta-cryptoxanthin are also converted to vitamin A, but only half as efficiently as beta-carotene.
Actually, of the 563 identified carotenoids, fewer than 10% can be made into vitamin A in the body. Some provitamin A carotenoids have been shown to function as antioxidants in laboratory studies; however, this role has not been consistently demonstrated in humans. Antioxidants protect cells from free radicals, which are potentially damaging by-products of oxygen metabolism that may contribute to the development of some chronic diseases.
Vitamin A is interesting for hematologists. The cell line HL60 is a myeloid leukemic cell line much loved by experimental hematologists. These blast-like cells can be made to differentiate into neutrophil granulocytes if exposed to vitamin A (vitamin D on the other hand turns them into monocytes) It appears that developing white cells have a receptor specifically designed for vitamin A.
Vitamin A deficiency is common in developing countries but rarely seen in the United States and Europe. Approximately 250,000 to 500,000 malnourished children in the developing world become blind each year from a deficiency of vitamin A. In Western countries, vitamin A deficiency is most often associated with strict dietary restrictions and excess alcohol intake. Strict dietary restrictions can also lead to zinc deficiency. Zinc is required to make retinol binding protein (RBP) which transports vitamin A. Therefore, a deficiency in zinc limits the body's ability to move vitamin A stores from the liver to body tissues.
Night blindness is one of the first signs of vitamin A deficiency. In ancient Egypt, it was known that night blindness could be cured by eating liver, which was later found to be a rich source of the vitamin. Vitamin A deficiency also contributes to blindness by making the surface of the eye very dry, thus it damages both the retina and the cornea.
As with other vitamins there has been interest in low storage levels of vitamin A that do not cause obvious deficiency symptoms. This supposedly mild degree of vitamin A deficiency is said to increase children's risk of developing respiratory and diarrheal infections, decrease growth rate, slow bone development, and decrease likelihood of survival from serious illness. Children living at or below the poverty level, who have children with inadequate health care or immunizations, especially those from immigrant communities and those with abnormalities of fat absorption are believed to be especially at risk.
Unless a person falls into one of these groups it is entirely likely that a normal diet will provide sufficient vitamin A. Three ounces of liver, for example, provides five times the daily requirement. Vegetarians and those who do not take dairy products will have to rely on the conversion of pro-retinoids from vegetables like carrots, cabbage, spinach or broccoli.
For those who like to take megadoses of vitamins, Vitamin A is one to be wary of. Overdoses are possible and can cause birth defects, liver abnormalities, reduced bone mineral density that may result in osteoporosis, and central nervous system disorders. The pro-retinoids have also been recommended as a prophylactic against cancer. A very large study of the use of beta-carotene had to be stopped when it was found that there was a 46% increase in lung cancer in those taking beta-carotene compared with controls.
However, retinoids can be used as medicines. For about 15 years synthetic retinoids (Roaccutane® or Accutane®)) have been used to treat certain skin diseases such as acne and psoriasis, and another retinoid, all trans retinoic acid (ATRA) is used to treat acute promyelocytic leukemia. Nevertheless, even these drugs should be avoided by those likely to get pregnant, and liver function tests should be monitored.
The daily requirement for vitamin A depends on your body size, but it is about 3000 international units and the safe upper limit of intake is 10,000 international units. 10,000 international unit is equivalent to about 3000 micrograms.
Thursday, January 08, 2009
Vitamins
This is the beginning of a new series of articles on Vitamins.
The word was coined by Sir Jack Cecil Drummond D.Sc., FRIC, FRS (12 Jan 1891—4 Aug or 5 Aug 1952). He was a distinguished biochemist, noted for his work on nutrition as applied to the British diet under rationing during the Second World War. He was murdered, together with his wife and 10-year old daughter, on the night of 4 Aug - 5 Aug 1952 near Lurs, a village or commune in the Basses-Alpes region (now Alpes-de-Haute-Provence) of Southern France. The name derives from 'vital amine' which Polish biochemist Kazimierz Funk contacted to 'Vitamine'. Drummond merely suggested dropping the final 'e' when it became clear that not all vitamins are amines.
The story of vitamins begins with Scottish surgeon James Lind who in 1749, the discovered that citrus foods such as lemons and limes prevented scurvy, disease of sailors in which collagen is not properly formed, causing poor wound healing, bleeding of the gums, severe pain, and death. In 1753, Lind published his Treatise on the Scurvy, which recommended using lemons and limes to avoid scurvy, which was adopted by the Royal Navy. So British sailors and later all Englishmen became known as Limeys.
Others such as Estonian surgeon Nikolai Lunin, Takaki Kanehiro, a British trained doctor of the Japanese Navy, Christiaan Eijkman, a Dutch pathologist working in the Dutch East Indies (now Indonesia) and Sir Frederick Gowland Hopkins OM FRS from Cambridge all made contributions to the realisation that some foods contained "accessory factors" in addition to proteins, carbohydrates, fats, etc. that are necessary for the functions of the human body. Hopkins and Eijkman were awarded the Nobel Prize in Physiology or Medicine in 1929 for the discovery of vitamins.
Vitamins are cheap and although we all need them, most are found in a normal diet. Some substances have been proposed as vitamins and are not and for some it has been proposed that we need far higher doses than are in a normal diet. We shall look at this proposition.
The story of vitamins is an exciting one and I shall enjoy writing it over the next few weeks.
The word was coined by Sir Jack Cecil Drummond D.Sc., FRIC, FRS (12 Jan 1891—4 Aug or 5 Aug 1952). He was a distinguished biochemist, noted for his work on nutrition as applied to the British diet under rationing during the Second World War. He was murdered, together with his wife and 10-year old daughter, on the night of 4 Aug - 5 Aug 1952 near Lurs, a village or commune in the Basses-Alpes region (now Alpes-de-Haute-Provence) of Southern France. The name derives from 'vital amine' which Polish biochemist Kazimierz Funk contacted to 'Vitamine'. Drummond merely suggested dropping the final 'e' when it became clear that not all vitamins are amines.
The story of vitamins begins with Scottish surgeon James Lind who in 1749, the discovered that citrus foods such as lemons and limes prevented scurvy, disease of sailors in which collagen is not properly formed, causing poor wound healing, bleeding of the gums, severe pain, and death. In 1753, Lind published his Treatise on the Scurvy, which recommended using lemons and limes to avoid scurvy, which was adopted by the Royal Navy. So British sailors and later all Englishmen became known as Limeys.
Others such as Estonian surgeon Nikolai Lunin, Takaki Kanehiro, a British trained doctor of the Japanese Navy, Christiaan Eijkman, a Dutch pathologist working in the Dutch East Indies (now Indonesia) and Sir Frederick Gowland Hopkins OM FRS from Cambridge all made contributions to the realisation that some foods contained "accessory factors" in addition to proteins, carbohydrates, fats, etc. that are necessary for the functions of the human body. Hopkins and Eijkman were awarded the Nobel Prize in Physiology or Medicine in 1929 for the discovery of vitamins.
Vitamins are cheap and although we all need them, most are found in a normal diet. Some substances have been proposed as vitamins and are not and for some it has been proposed that we need far higher doses than are in a normal diet. We shall look at this proposition.
The story of vitamins is an exciting one and I shall enjoy writing it over the next few weeks.
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