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Vitamin C
Ascorbic acid. A water soluble vitamin which is easily destroyed by cooking and by contact with alkaline substances. Some vitamin C is lost in freezing and preserving, and it is also easily oxidised.
Deficiency
At its extreme, vitamin C deficiency causes scurvy, a disease characterised in its early stages by swelling and bleeding gums, loosened teeth, followed by muscular weakness, joint damage and subcutaneous haemorrhages. Less extreme shortage of this vitamin leads to tender joints, bleeding gums, fatigue, general weakness, lowered resistance to disease and muscle degeneration. The body needs to build up a reserve of ascorbic acid, by receiving regular daily supplies: scurvy is still a problem today during the long winter months in Scandinavian countries where fresh fruit and vegetables are in short supply, and the body's reserves are depleted.
Overdose
Large doses of vitamin C can generally be taken without any problems, though some people may find that they have stomach problems with an intake of several grams a day. It is best to increase and decrease the amount taken gradually, as a sharp increase in vitamin C can cause diarrhoea, while suddenly cutting off a high daily dose can cause fatigue.
Benefits
Vitamin C is vital for the formation of collagen and connective tissue - tendons, ligaments and cartilage. It maintains the strength of the walls of blood vessels and helps the body to absorb iron. It helps fight infection and diseases such as high blood pressure, arteriosclerosis and cancer.
In larger doses, it is an antioxidant, mopping up the oxygen free radicals that destroy cells and cause ageing. It also makes an important contribution to the antioxidant action of other vitamins, particularly vitamin A and vitamin E. Caution is required in preparing foods to gain maximum benefit from the vitamin C. If the vitamin itself becomes oxidised, it will encourage the production of free radicals, rather than fighting them. Oxidation can be caused by the metals iron and copper in food when the vitamin C's cell membranes have been weakened by cooking.
It is believed that ascorbic acid in larger doses may help prevent cancer by stopping the formation of carcinogenic nitrosamines from nitrates and nitrites present in food. It also improves the function of while blood cells, which fight viruses, bacteria and cancer cells.
In conjunction with vitamin B1 and the amino acid cysteine, vitamin C helps to counteract the damaging chemicals produced in the body by alcohol, nicotine, exhaust fumes and the toxic heavy metal, cadmium.
Recent studies show that vitamin C also helps to prevent the formation of bad cholesterol and reduces levels of LDL cholesterol in the body. It may thus be involved in protecting us from high blood pressure and arteriosclerosis.
Sources
Vitamin C is found in citrus fruit, berries, tomatoes, peppers, broccoli, cauliflower, potatoes, fresh green vegetables and chillies. Remember how easily it is destroyed by heat, light and freezing - try to eat fresh, uncooked fruit and vegetables for maximum vitamin C.
RDA (Recommended Daily Allowance)
The RDA for vitamin C is 60 mg for a healthy adult. Pregnant women, smokers and heavy drinkers need more. All RDAs are calculated as the minimum levels required in order to prevent the occurrence of well-known vitamin deficiency symptoms.
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, as shown above.
Vitamin D
Vitamin D is actually a group of hormone-like chemicals called steroid alcohols. The vitamin group is fat-soluble and quite stable: it won't be lost in storage, cooking or processing. The skin is able to manufacture vitamin D - up to 10 IU per square centimetre, depending on the level of pigmentation (darker skins produce less) and the amount of air pollution (pollution absorbs ultraviolet light, preventing so much of it penetrating the skin and thus enabling the production of the vitamin).
Deficiency
The extreme deficiency condition is rickets, where childrens' bones grow irregularly and become soft, leading to distorted limbs, swollen joints and chest deformities. Although still seen in the third world, rickets is rare in industrialised countries. In adults, the equivalent condition is osteomalacia, where calcium is withdrawn from the bones, softening them and causing pain, weakness and fractures. This condition is most likely to occur during pregnancy. Less extreme shortage of vitamin D can lead to dental caries in children, muscle weakness and cramp, and if it is prolonged, osteoporosis. It is absorbed through the small intestine, and requires bile for the process. So diseases of the pancreas, gall bladder, liver or intestine, can reduce the absorption of vitamin D
Overdose
One of the main functions of vitamin D is to enable the body to absorb calcium and phosphorus, and because of this, excess amounts of the vitamin can be harmful, leading to over-calcification of the bones and teeth, formation of calculus stones in the kidneys and hardening of the arteries due to calcium deposits. Early signs of overdose include itchy eyes and skin, unquenchable thirst, diarrhoea and generalised physical discomfort.
Benefits
Vitamin D acts like a hormone, affecting processes in various parts of the body. It is essential to the absorption of calcium and phosphorus, so it is essential to the proper development and continued health of teeth and bones. It also regulates the permeability of cell membranes.
Sources
Vitamin D is found in animal fats, such as butter, eggs, liver, oily fish (kippers, mackerel, sardines and tuna), margarine, full-fat dairy products and evaporated or malted milk. Milk is not in itself a good source of vitamin D, unless it has been fortified (this is done routinely in the United States, Canada and many other countries, although not in Britain.) It is possible to buy dairy milk and soya milk fortified with vitamin D in this country, from specialist suppliers.
RDA (Recommended Daily Allowance)
The RDA for vitamin D is around 400 IU for adults, 1000 IU for babies up to 2 years and between 500 - 1000 for older children. Pregnant women should have between 400 - 800 IU per day. If a reasonable diet is eaten, supplements are not likely to be needed except perhaps during the dark winter months, for children and the elderly.
Vitamin E
Once again, this vitamin is actually a group of chemical compounds which all act in the same way. The most common is alpha-tocopherol (it also exists in beta- gamma- and delta- forms). The body cannot produce vitamin E, so we we have to get it from our diet. It is fat-soluble.
Deficiency
Lack of vitamin E causes reproductive problems - infertility, increased risk of miscarriage, etc. It also causes degeneration of the kidneys and general wasting symptoms.
Overdose
It is almost impossible to overdose on vitamin E. Large scale studies have shown that people can take up to 10 grams a day for extended periods without adverse effects, though some individuals find that doses in excess of 1 gram a day can cause stomach problems.
Benefits
Vitamin E is known to be essential for muscle development and for preventing the red blood cells from breaking down. It also believed to be important in maintaining reproductive health, though it is not yet clear by what mechanism. It protects against miscarriage by promoting the healthy development of the foetus. It also has a vital role as an antioxidant, protecting cells from attack by free radicals and peroxides. The more research is carried out, the more beneficial results seem to be attributable to vitamin E. It can help to prevent cancers developing, when taken in combination with selenium, and seems to reduce the unwanted side effects of radiotherapy and chemotherapy. At high doses (800mg a day) it acts as an anticoagulant, preventing the formation of clots and thromboses, and has been found to be beneficial in correcting cardiovascular disorders like intermittent claudication - though this latter typically takes several months to show improvement. It is generally helpful in boosting the immune system and increasing resistance to viral and bacterial infection, in doses of between 5 - 20mg per kilo of body weight (350 - 1400mg for someone weighing 70kg). For cataract prevention, daily doses between 300 - 400 mg are effective, particularly combined with vitamin C and beta-carotene. Recent studies suggest that, in common with other anti-oxidants, it may have a contribution to make in preventing the onset of Parkinson's disease, or slowing the deterioration it causes: doses of 400 - 3200 mg combined with 300mg of vitamin C seem beneficial. Scandinavian research indicates that a 400 mg supplement of vitamin E with selenium can give a significant boost to the physical and psychological health of elderly people.
Sources
Good sources of vitamin E include wheatgerm, soya, corn and peanut oils, margarine, raw nuts and seeds, eggs, butter, yams, liver and some green leafy vegetables. It is, however, quite easy to destroy vitamin E by freezing, processing, preserving and simple contact with the air.
RDA (Recommended Daily Allowance)
The RDA is about 12mg, but the notes above highlight the effects of this vitamin in quantities well above the RDA.
Vitamin H
Also known as biotin - and still the subject of debate as to whether it is a vitamin in its own right, or part of the B complex. It is water soluble, and is manufactured in the body by intestinal bacteria in quantities that are sufficient to meet most requirements.
Deficiency
Deficiency can occur, particularly in elderly people, athletes and epileptics - all of whom tend to have relatively low levels of biotin in their blood. Symptoms include loss of appetite, infections of the mucous membranes, depression, insomnia, rashes, increased blood cholesterol levels. Rarely, children may develop a form of eczema or a fungal skin disorder due to biotin deficiency, but these and all other symptoms can be relieved very quickly with a simple daily supplement.
Overdose
No cases of biotin overdose have ever been reported.
Benefits
Biotin is part of the process which produces energy from dietary glucose, and also the production of glucose from non-carbohydrate sources (amino acids). It boosts the efficiency of the immune system and helps with the manufacture of antibodies. Trials have been conducted in which it was used to stop hair loss, in combination with various minerals and other compounds, but the results were mixed.
Sources
It is found in liver, kidney, egg yolk, yeast, oats, nuts, milk chocolate and most vegetables.
RDA (Recommended Daily Allowance)
The RDA for men and women is 60 micrograms.
Vitamin K
This fat soluble vitamin exists in three forms: phytomenadione, menaquinane and menadione. Essentially it is a group of similar compounds, called quinones, which are required for a healthy body. Most of the vitamin K we need is produced by bacteria in the intestine.
Deficiency
Deficiency may prevent the blood from clotting properly, and trigger the development of osteoporosis, as vitamin K is required for calcium to form new bone. People with conditions that prevent the proper absorption of fat may have a deficiency, as may alcoholics and anyone who doesn't eat sufficient green vegetables. Prolonged use of antibiotics also reduces the body's ability to make vitamin K.
Overdose
Too much vitamin K could cause jaundice in babies.
Benefits
The vital functions of vitamin K are associated with formation of coagulation factors, which clot the blood so that wounds can heal properly, and the proper calcification of bones. It has been shown that vitamin K supplements reduce the loss of calcium from the bones of osteoporosis sufferers, and speeds the healing of healing of bone fractures. Supplements are sometimes given to patients before major surgery.
Sources
It is found in green vegetables, seaweed, potaotes, liver, eggs, wheatgerm, fish, nuts, alfalfa, molasses, yoghurt, dairy products, corn oil and soya oil.
RDA (Recommended Daily Allowance)
There is no official RDA, but an average adult requirement is 1 mg.
Vitamin P
Also known as bioflavinoids. This group of pigments occurs in fruits and vegetables that are yellow or orange in colour.
Deficiency
Deficiency leads to bleeding from the tiny blood capillaries into the surrounding tissue, and an inability for the body to absorb and metabolise vitamin C properly.
Overdose
No cases are known.
Benefits
Vitamin P works to strengthen the walls of the blood vessels, and it is essential for the body to use vitamin C properly. Some athletes take a supplement as they believe bioflavinoids will help joint and muscle injuries to heal more quickly. They can also help to reduce high blood pressure (hypertension).
Sources
Found in citrus fruits, carrots, rosehips, plums.
RDA (Recommended Daily Allowance)
There isn't an official RDA, and it is thought that the human requirement is very small.