Our understanding of vitamins has come a long way in the two centuries since an English naval doctor showed that adding citrus fruit to sailor's diets could prevent scurvy.

What are vitamins?

The word vitamin is derived from the term 'vital amine', given to vitamins by the scientists who discovered them and who believed they were chemicals called amines.

We now define vitamins as any group of substances necessary in very small amounts for healthy growth and development. We know that because they cannot be synthesised in the body they are essential constituents of our diet. They fall into two groups: those that are water-soluble (including the vitamin B complex and vitamin C), and those that are fat-soluble (including vitamins A, D, E and K).

Vitamin requirements

What vitamins do, and where they are to be found, is well-documented in both consumer and professional publications [14]. But beliefs about how much of each vitamin we need to remain healthy have changed in recent years. Out are the recommended daily allowances (RDA) and in is official recognition that we are all different and may, therefore, have different vitamin requirements. In 1991, a report by the Committee on Medical Aspects of Food Policy, from the Panel on Dietary Reference Values, introduced four new measures of vitamin requirements [5].

• Estimated average requirement (EAR) - the average requirement or need for food energy or a nutrient. Some people will need more, others less.
• Reference nutrient intake (RNI) - an amount of a nutrient that will be sufficient for almost everyone, even someone with a high need for that nutrient. RNI is equivalent to the old RDA.
• Lower reference nutrient intake - an amount of a nutrient that is enough only for those with low needs, so it is likely to be insufficient for most people. Anyone having less than the LRNI will almost certainly be deficient.
• Safe intake - this indicates the intake of a nutrient for which there is not enough information on which to base an estimate of our requirements. A safe intake is one that is judged to be 'adequate' for almost everyone's needs but not large enough to cause undesirable effects.

The UK now has to comply with European Union legislation and all vitamin supplements must have European recommended daily allowances (ROA) on their labels. Many believe that these ROA have little scientific value and debate continues in Europe. The Department of Health has steered clear of making many recommendations regarding vitamins, with the exception of folic acid (see Box 1) and vitamins A and D supplements for babies of more than six months for whom breast-milk is the main source of nutrition [6]. The official view is that most people get enough vitamins from their diet and it is a matter for their doctor if they do not. (See Box 2 for a list of people who may require a higher vitamin uptake).

Box 1. Folic acid update

Folic acid is known to help prevent neural tube defects such as spina bifida, and the Department of Health recommends that women planning a pregnancy take folic acid tablets as a supplement and continue taking them until the 12th week of pregnancy [9]. The DoH also encourages women to eat foods rich in folic acid. However, research published in March 1995 suggests that, compared with supplements and fortified food, consumption of extra folate as natural food folate is relatively ineffective in increasing folate status. The researchers believe that 'advice to womm, to consume folate-rich foods as a means to optimise folate status is misleading' [10].

For more information on spina bifida contact: Association for Spina Bifida and Hydrocephalus, ASBAH House, 42 Park Road, Peterborough, PE1 2UQ.

Box 2. Extra needs

The following groups may need extra vitamins:

• Those on restricted diets, for instance people with diabetes, vegans, people with coeliac disease, people with allergies.
• People with poor appetites; for example, frail older patients, those who are ill; people who do not eat a wide range of foods; for example, faddy children.
• Those convalescing from illness.
• People with a weakened immune system.
• People with digestive disorders.
• Menstruating women.
• Pregnant and breast-feeding women.
• Slimmers whose reduced calorie intake has led to poorer nutrient levels.
• Smokers and drinkers.
• Athletes and very active people.

Yet in the UK we spend more than 100m a year on vitamin and mineral supplements [7]. Fears about the quality of our food and a belief that taking supplements is a good preventative measure are both factors that influence our decision to take such supplements. The Consumer's Association takes the view that most people do not need them but those who wish to take extra vitamins should take a good multivitamin supplement [7].

According to Walji, a multivitamin tablet or capsule should contain: Vitamin A, beta carotene, vitamins C,D,E and the minerals phosphorus, calcium, magnesium, potassium, iron, zinc, manganese, copper, iodine, molybdenum, chromium, selenium, vanadium choline, inositol, methionine, PABA, bioflavinoid, lysine, lecithin, rutin, betaine, hesperdine and cysteine [2]. Possible benefits of taking a multivitamin supplement include [1]:

• Maintaining good general health
• Ensuring adequate vitamin intake when on a restricted diet
• Improving resistance to minor illness.

Choosing a supplement

Simply swallowing a multivitamin does not mean you will benefit from all the nutrients in the tablet. Poorly made supplements may pass through the body without even dissolving.

An undesirable addition to vitamin supplements is sugar, yet many supplement labels reveal that sugar, in some form or other, has been added. Checking the label before purchasing a vitamin supplement is important for people with particular medical conditions, such as diabetes, or those following a particular diet, such as an anti-candida diet.

Box 3. Recent research

Vitamin E

A study of 2002 patients with coronary atherosclerosis showed that taking a daily high-dose vitamin E supplement reduced the risk of heart attack by 75% [11].

Vitamin C

A survey (unpublished), funded by the National Asthma Campaign, of more than 2000 people aged between 18 and 70 suggests that the more vitamin C that people eat, the better their lung function.

Another source of controversy is high-potency vitamins. Generally speaking, there is rarely any benefit in taking more than the RNI, since the excess will either be excreted, if the vitamin is water-soluble, or stored, if fat-soluble. Research on high-potency vitamins has shown they have therapeutic value in some cases (see Box 3). Large doses of vitamins A and D can produce toxic effects, including birth defects [8], and can interfere with absorption of other nutrients [2].

Time-release supplements are also available. These allow the ingredients of a vitamin tablet to trickle out of a binding matrix over a prolonged period. This has some benefit when taking water-soluble vitamins, since they cannot be stored in the body.

Some vitamin products are advertised as being 'natural' or 'organic', but there is little that is naturao about the extraction and purification process associated with vitamin manufacture, and such products are usually more expensive.

Recent developments

Research continues into the particular health benefits of vitamins for different diseases and conditions. In the past year, for example, there has been research into vitamin E and coronary heart disease, and the protective value of vitamin C for people with respiratory conditions such as asthma (see Box 3).

This year may see more European debate relating to nutritional supplements, as the European Union gears up to publish a discussion document aimed at finding a way of harmonising this market (see Box 4).

© Joanna Trevelyan (1996) Nursing Standard 92, 22, 48-50.

Box 4. European view

Last year fears receded in the UK that vitamins, minerals and other nutritional supplements would need a full product licence in order to comply with a European Union directive. It was decided that they fell outside the remit of the directive because production techniques of the supplements were different to those of medicines.

More recently, member states have become concerned that differences in the controls on dietary supplements within the EU are causing increasing trade problems. According to a spokesperson for the Ministry of Agriculture, Fisheries and Foods, the European Commission has concluded that these problems have become sufficiently important for it to consider how they might be dealt with. A discussion paper is being prepared by the EC for consideration by member states but is unlikely to be issued before the summer. MAFF will 'consult fully' before deciding the UK's response.

A ministry spokesperson said: 'In previous discussions the UK made it clear that any strategy for dealing with the trade problems associated with dietary supplements should not automatically lead to regulation. The UK would wish to ensure that any EC proposals are proportionate to the need. We would want to ensure that consumers are given as much choice as possible in the area of dietary supplements, providing that public health is not compromised.'

References

1. Dowden A, Lacey G The Consumer Guide to Vitamins: How to Choose Vitamins, Minerals and Other Food Supplements. London; Pan Books, 1996.
2. Walji H Vitamins, Minerals and Dietary Supplements: A Definitive Guide to Healthy Eating. London; Headway, 1995.
3. Trimmer E The Good Health Food Guide: How to Choose Health Foods and Supplements to Boost Your Health. London; Piatkus, 1994.
4. Department of Health Eat Well: Action Plan from the Nutrition Task Force to Achieve the Health of the Nation Targets for Diet and Nutrition. London; DoH, 1994.
5. Department of Health Dietary Reference Values for Food Energy and Nutrients for the United Kingdom. (Report of the Panel on Dietary Reference Values of the Committee on Medical Aspects of Food Policy.) London; HMSO, 1991.
6. Department of Health Weaning and the Weaning Diet. (Report of the Working Group on the Weaning Diet of the Committee on Medical Aspects of Food Policy.) London; HMSO, 1994.
7. Consumer's Association. Vitamins and Minerals. Which? 1995; 8; 1; 1.
8. Rothman KJ, Moore LL, Singer MR et al. Teratogenicity of high Vitamin A intake. New England Journal of Medicine. 1995; 33; 21; 1369-1373.
9. Department of Health Folic Acid and the Prevention of Neural Tube Defects. London; DoH, 1992
10. Cuskelly GJ, McNulty H, Scott JM. Effect of increasing dietary foliate on redcell folate: implications for prevention of neural tube defects. Lancet. 1995; 347; 657-659.
11. Stephens NG, Parsons A, Schofield PM et al. Randomised controlled trial of vitamin E in patients with coronary disease: Cambridge Heart Antioxidant Study (CHAOS). Lancet. 1996; 347; 781-786.