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Vitamin A and beta-carotene
A fat-soluble vitamin, which is actually a group of chemical compounds including retinol, retinal, carotene and carotenoids. Carotenes are precursors to vitamin A - ie, they are converted into vitamin A in the liver.
Deficiency
One of the key areas in which vitamin A is important is in the healthy functioning of the eye. Deficiency can lead to a range of conditions, including night blindness, abnormal sensitivity to light, painful conjunctiva and red, swollen eyelids. Apart from the eye, lack of vitamin A can prevent proper development of the teeth and normal body growth (in children), and cause skin eruptions, reduced resistance to infections and problems with the mucous membranes (moist membranes which line many tubes and cavities in the body, such as the nose and respiratory system; mouth and digestive tract, and the urinary system).
Overdose
Because vitamin A is fat-soluble, rather than water-soluble, excess supplies are stored in the liver, where it lasts for 200 - 300 days, rather than being flushed out of the body on a daily basis. This means that in cases where high doses have been taken over a long period of time, it is possible to have vitamin A poisoning. Symptoms are dizziness, nausea, headaches and vomiting. Early signs of excess vitamin A consumption are dry and itchy skin.
Benefits
Vitamin A and beta-carotene are important to the healthy functioning of the eye, as has already been noted. They are also now known to be useful in treatment of skin disorders, including photosensitivity - where exposure to sunlight leads to burns, rashes and lesions - and psoriasis and acne. Beta-carotene protects skin from the effects of too much sunlight (make sure you're topped up before you hit the beach!)
Beta-carotene also has an important anti-oxidant effect. This means that it helps the body to get rid of so-called free radicals - the unstable oxygen atoms that build up in the body and have been implicated in harmful changes to the structure of our DNA, leading to many diseases, including the development of cancerous tumours, and the general physical deteriorations associated with the ageing process.
The anti-oxidant effects seem to be enhanced when vitamin A is taken in conjunction with vitamin E and the mineral selenium.
Vitamin A and beta-carotene are given to cancer patients who are receiving radiotherapy or chemotherapy treatments. These treatments produce free radicals which are supposed to attack tumour cells, but also cause damage to healthy tissue and reduce the levl of enti-oxidant chemicals in the blood. The vitamin A and beta-carotene help to reduce these unwanted side-effects.
Sources
Vitamin A occurs in many foods, particularly butter, egg yolk, liver, kidney, green vegetables and yellow/red fruits and yellow/orange vegetables. Note that carrots and tomatoes are best eaten cooked, rather than raw, if you are to gain the maximum from these rich sources of beta-carotene.
Vitamin A is readily available as a supplement, for anyone who requires a larger amount than they can obtain from their diet.
RDA (Recommended Daily Allowance)
The RDA for vitamin A is 5000 IU (about 1mg). All RDAs are calculated as the minimum levels required in order to prevent the occurrence of well-known vitamin deficiency symptoms. They are produced for the guidance of an "average", healthy individual, and do not take account of the different needs of pregnant and nursing mothers, smokers, people with chronic diseases or on long-term medication, those with metabolic disorders and those over 50.
Since the idea of RDAs was generally accepted, much more has been learnt about the benefits of various vitamins, and doses well above RDA levels are commonly used to help prevent disease and boost the immune system.
8000 IU per day is believed by doctors to be perfectly safe - even during pregnancy where foetal damage can be caused by vitamin A overdose - and doses of 20,000 to 25,000 IU per day can be taken if required over extended periods of time.
Vitamin B1
Thiamin, thiamine, aneurine - vitamin B1 is a water-soluble vitamin which is part of the B group. All water-soluble vitamins are easily destroyed in food preparation and cannot be stored in the body in any quantity - so levels need to be replenished on a daily basis.
Deficiency
It is calculated that about half the population in industrialised countries suffers from long-term low-level vitamin B1 deficiency. Symptoms are anxiety, irritability and depression - but these symptoms change if the deficiency becomes greater, to include loss of weight and appetite, and ultimately, paralysis, wasting of limbs and a disease called beriberi where muscular weakness and nerve inflammation can eventually lead to heart failure.
Overdose
Even at levels 300 times the RDA, thiamin causes no particular toxic effects. Because it is water soluble, excess amounts are removed from the body in the urine.
Benefits
This vitamin promotes normal metabolism, digestion and body growth, and is important for the health of the nervous system and blood circulation. It improves the functioning of the T-cells ( one of the white blood cells) and is essential for the brain to develop and function normally.
It is an anti-oxidant, protecting cells from acetaldehyde, a cancer-causing substance which builds up in cells due to the action of free radicals.
B1 works best in association with the other B vitamins - they enhance each others actions.
It has been used to help remove the free radicals produced by cancer, arteriosclerosis and arthritis, and can help with alleviating a range of minor pains, like toothache, seasickness and smoker's cough.
Sources
The best sources are yeast, the husk of grains (such as brown rice), wholewheat products (bread, pasta, etc) peas, beans, potatoes, nuts and eggs.
RDA (Recommended Daily Allowance)
The RDA for vitamin B1 is 1.5 mg. This minimum level does not take account of the fact that stores of the vitamin are depleted by a range of everyday factors, such as stress, drinking alcohol and coffee, taking various medications (including the contraceptive pill), smoking, eating carbohydrates. Elderly people and pregnant women require more thiamin, too.
Vitamin B2
Also known as riboflavin, lactoflavin or vitamin G - vitamin B2 is a water-soluble vitamin which is part of the B group, and can be partially decomposed by heat and sunlight. It cannot be stored in the body in any quantity - so levels need to be replenished on a daily basis.
Deficiency
Once again, low-level deficiency is believed to be very widespread in the western world, with pregnant and nursing mothers, the elderly, vegans, the chronically ill and slimmers all particularly at risk. Various drugs, including antibiotics, tranquillizers and contraceptive pills can all reduce riboflavin levels. Diseases such as tuberculosis and arthritis can cause deficiencies. Symptoms include insomnia, dizziness, hair loss, inflammation of the tongue and lips, scaly scalp and eczema, oversensitivity to light. Riboflavin is absorbed by the small intestine, in a process regulated by the thyroid hormones - so any medications which affect the working of the thyroid gland may have an impact on the body's absorption of the vitamin.
Overdose
It is almost impossible to overdose on riboflavin: the upper limit is 3g per kg of body weight and the RDA is between 1.3 and 1.7 mg. Riboflavin is stored in the red blood cells, primarily, excess amounts being removed from the body in the urine or faeces.
Benefits
Vitamin B2 helps in releasing energy from carbohydrates. It also has a role to play in producing the neurotransmitters serotonin, noradrenaline and acetylcholine, as well as histamine, which is released from tissue cells after they've been damaged. The vitamin is involved in the synthesis of essential fatty acids, linoleic acid, linolenic acid and arachidonic acid.
Sources
Riboflavin is found in many foods, including milk, cheese, eggs, fish, liver, yoghurt, green vegetables, pulses and yeast extract.
RDA (Recommended Daily Allowance)
The RDA is between 1.3 and 1.7 mg. See the notes above about the likelihood of deficiency.
Remember that all RDAs are calculated as the minimum levels required in order to prevent the occurrence of well-known vitamin deficiency symptoms. They are produced for the guidance of an "average", healthy individual, and do not take account of the different needs of pregnant and nursing mothers, smokers, people with chronic diseases or on long-term medication, those with metabolic disorders and those over 50.
Since the idea of RDAs was generally accepted, much more has been learnt about the benefits of various vitamins, and doses well above RDA levels are commonly used to help prevent disease and boost the immune system.
Vitamin B3
Also known as niacin, nicotinic acid, nicotinamide, nicotinate. Niacin can be manufactured in the body, from an essential amino acid called tryptophan, but it is only made in small quantities, so most of our daily requirements must be met from dietary sources. It is a water-soluble vitamin, so can easily be destroyed by heat, bright light and cold.
Deficiency
Niacin deficiency leads to fatigue, muscle weakness, loss of appetite, irritability, skin eruptions, nausea, vomiting, headaches, tension, insomnia. At the extreme, deficiency causes pellagra, a disease characterised by dermatitis, inflamed mucous membranes, diarrhoea and severe mental disturbance, which can lead to death if not treated with niacin supplements.
Overdose
Again, it is hard to overdo this water-soluble vitamin, but the sypmtoms
of overdose inlude flushing and tingling skin,
paresthesias (abnormal nerve sensations such as pricking, tingling, pins-and-needles),
gout, diabetes-like symptoms, hyperglycaemia.
Benefits
Vitamin B3 is important in food metabolism and the breakdown of glucose. It helps with the efficient circulation of the blood, expanding the arteries and reducing resistance to the flow of the blood. It reduces low density lipoprotein (LDL-cholesterol), the 'bad' cholesterol, which contributes to hardening and narrowing of the arteries, a precursor of heart disease. With the other B vitamins, niacin has an antioxidant effect, and it has been used in conjunction with vitamin C as a substitute for sleeping pills and tranquillizers.
Sources
It is found in meat, poultry, liver, kidney, eggs, nuts, fish cheese, peas, beans, milk, dried fruit, yeast extract and rice.
RDA (Recommended Daily Allowance)
The RDA is 18 mg, but more than this amount is routinely required by men, pregnant women, nursing mothers, and anyone who is short of the other B vitamins - B1, B2 and B6 - which help the body convert tryptophan into niacin. The contraceptive pill also seems to have a negative impact on the formation of niacin.
Vitamin B5
Pantothenic acid or pantothenate is water-soluble. It is fairly resistant to heat, so won't be destroyed by frying, baking, etc - though the very high temperatures associated with pressure cooking will destroy it, as will freezing.
Deficiency
As vitamin B5 is present in almost all foods, cases of deficiency are extremely rare. The symptoms include muscle cramps and weakness, insomnia, fatigue, asthma, reduced resistance to infections.
Overdose
Any surplus pantothenic acid passes unaltered through the body, being eliminated in the urine and excreta.
Benefits
B5 fulfils many functions. It is essential in metabolising sugars, fats and proteins; growing new cells for healthy skin and hair; facilitating the functioning of the steroid hormone cortisone and enabling the body to use choline and PABA (para-aminobenzoic acid). Most importantly, it plays a part in assisting the production of antibodies, thus helping the body to fight off disease.
Sources
As stated above, vitamin B5 is found in most foods and generally, people obtain sufficient quantities from their diet not to require any supplementation.
RDA (Recommended Daily Allowance)
The RDA is 10 mg.
Vitamin B6
Pyridoxine, pyridoxal, pyridoxamine. A water soluble vitamin that is rapidly metabolised and distributed throughout the body.
Deficiency
Deficiency in B6 manifests itself through loss of appetite, anaemia, depression, fatigue, apathy, insomnia and poor memory. Children and babies are more at risk of deficiency, which can produce convulsions, as well as anaemia and irritability. Woman who are deficient may experience more painful periods.
It has been found that elderly people, pregnant women, women taking the contraceptive pill and people who consume large amounts of alcohol are more likely to be deficient. Some medicines, such as penicillamine (anti-arthritic) counteract the effects of vitamin B6, leading to deficiency unless supplements are taken.
Overdose
Very large doses (more than 1000mg) can cause poisoning and damage to the peripheral nervous system.
Benefits
This vitamin fulfils many functions in the body, from improving disease resistance and maintaining healthy skin and nerves to forming red blood cells and preventing premature ageing. It is important in enzyme reactions and brain function, and maintains the balance in the body between sodium and potassium ions. It allows the body to utilise the mineral selenium and partially controls the proper functioning and repair of the nervous and musculo-skeletal systems. Many women find a B6 supplement helpful in dealing with painful periods, PMT and endometriosis.
Sources
Vitamin B6 is found in many foods, inlcuding green vegetables, brewers yeast, fish, pulses, milk, liver, whole grain cereals, nuts, raisins and prunes.
RDA (Recommended Daily Allowance)
The RDA is 2 mg for women and 2.2 mg for men, but more is required by pregnant women, nursing mothers, people on a high-protein diet and those who have chronic diseases. The contraceptive pill interferes with the body's take up of B6, and those with a chronic intestinal condition such as gluten allergy will also need more.
Vitamin B9
Also known as Folic Acid, this is a water-soluble vitamin which is rapidly destroyed by cooking. The body holds very small reserves, so it is important to keep levels topped up.
Deficiency
Lack of folic acid is often reckoned to be the commonest vitamin deficiency in the world, and it is particularly a problem amongst elderly people, pregnant women and those taking the pill, people with high alcohol consumption and those with intestinal problems. Deficiency can lead to anaemia, depression, apathy, dizziness and shortness of breath. Shortage of folic acid during pregnancy can lead to spina bifida in the developing foetus. Some treatments for cancer and for urinary tract infections counteract the effects of folic acid, meaning that supplements must be taken to prevent deficiency.
Overdose
Unlikely, but too much B9 can lead to masking of a B12 deficiency (see below) which could lead to irreversible nerve damage. It may also cause seizures in epileptics.
Benefits
Folic acid helps in the formation of nucleic acids, such as DNA, which are made when new cells are produced - so it is vital to tissue repair and the manufacture of new red blood cells. It assists with digestion and may help to protect women against cervical cancer.
Sources
Folic acid was first isolated from spinach leaves, and this as well as other green vegetables, asparagus, liver, kidney, yeast, nuts and whole grains are the best sources.
RDA (Recommended Daily Allowance)
The RDA is 400µg though pregnant women need twice as much.
Vitamin B12
Cyanocobalamine, cyanocobalamin - a water soluble vitamin containing cobalt. Its action is associated with that of folic acid (vitamin B9 - see above). It can only be absorbed through the gastrointestinal tract, with the presence of the 'intrinsic factor' - a glycoprotein produced in the intestine - and calcium.
Deficiency
Deficiency, caused either by a shortage of the vitamin itself or the intrinsic factor required for its absorption, can cause pernicious anaemia, brain damage and deterioration of the nervous system, with symptoms such as poor coordination and loss of sensation. Continued deficiency produces a range of symptoms including fatigue, irritability, loss of appetite, diarrhoea, circulation problems and a yellowing of the skin.
Overdose
Overdosing is unlikely, but could lead to iron or folate deficient anaemia.
Benefits
Vitamin B12 is essential for production of red blood cells and the myelin sheath protecting the nerves. It enables the body to use vitamin B9 (folic acid) correctly, and assists in preventing cell degeneration and in metabolising fats, carbohydrates and proteins to produce energy.
Sources
Cyanocobalamine is found in animal food sources: liver, fish, eggs, meat, kidney, cheese, as well as fortified breakfast cereals and brewer's yeast.
RDA (Recommended Daily Allowance)
Men - 220 µg, women - 400 µg. However, according to several recently published studies, much higher quantities - up to 20 grams per day - may be consumed without danger, and many researchers now believe that the lower RDA could leave the body vulnerable to low blood cell production, reduction in protein metabolism, and a higher risk of birth defects.
Vitamin B15
Calcium pangamate, pangamic acid. This is a controversial supplement which is variously described as a vitamin or a pro-vitamin. It was first isolated from apricot kernels in 1951, and has been used in supplements since the 1960s, with many claims for its benefits most of which have subsequently been refuted.
It has not been shown in any scientific studies to boost energy or improve athletic performance - though it was popular with Soviet-era athletes for just these alleged qualities.
It's claimed ability to control seizures has also been disproved.
The jury is still out in its possibilities as an immune-system booster. Some trials with animals seem to support this - but no studies are yet available showing similar results in humans.
Apart from apricot kernels, vitamin B15 is also found in rice husks, ox blood, brewer's yeast, maize and other plants.
There are no known cases of overdose - the usual daily dose is 125 mg, and there is no RDA as the government agencies which produce them are not convinced that there are any health benefits from this substance.
Vitamin B17
Also known as amygdalin, and by the trade name laetrile, this is another controversial member of the B vitamin family, with some researchers unconvinced that it is actually a vitamin.
Found particularly in almonds and apricots, amygdalin is believed by some to have a role in preventing cancer, or even as a treatment for cancer. This action is believed to come about because the compound produces hydrogen cyanide in the tissues of the body, which attacks and destroys cancer cells. Unfortunately, it also does the same with healthy ones...
The research on the benefits of B17 has produced contradictory results, but many scientists now believe that it may actually cause cyanide poisoning or cancer.