The use of vitamin and mineral supplements is growing rapidly. This article describes the effects of common supplements and asserts that for most people they are an unnecessary waste of money. However, they can be a useful adjunct to the diet for certain vulnerable groups.

Dietary supplements are big business. In 1997 the UK population spent £335 million on vitamins, minerals and other dietary supplements. It is predicted that by 2001 this figure will rise to around £500 million (Mintel 1997). The market is undoubtedly growing, fuelled by media interest, the claims and counter-claims of the various products and by 'alternative' therapists who promote their use as part of the cure of a particular disease or ailment.

As the science (and science fiction) relating to nutrition expands, links may be made between certain dietary constituents and their beneficial effects in the body, and on reductions in the likelihood of suffering from various diseases. If the story is good the media get involved. Selenium is an example of a nutrient relatively unknown by the general public, which recently hit the headlines. 'Selenium can bring back youthful vigour' stated The Times (Reilly 1997), 'Can Selenium really beat cancer?' asked the Daily Mail (Reilly 1997). These media stories fuel public interest and often a rash of dietary supplements containing the new miracle nutrient hits the market.

But are these supplements safe, who really needs them, and how can people be sure that they are taking the product most suited to their particular needs?

Who takes supplements?

Many people take a vitamin pill 'just in case'. They use them because they believe more must be better, or as insurance against their diet not being up to scratch. In fact, evidence shows that the people who take supplements are those least likely to need them (Gregory et al 1990, Kirk et al 1999).

In the Dietary Survey of British Adults (Gregory et al 1990) it was found that 17% of women and 9% of men took supplements, and they were most commonly taken by people from social classes I and II. The most popular supplements were multivitamins with or without iron, followed by fish liver oils and vitamin C. Intakes of all vitamins from food alone were found to be higher in those taking supplements compared to those who did not.

To investigate the 'inverse supplement hypothesis' further, Kirk et al (1999) analysed data from over 13,000 subjects from the UK Women's Cohort Study, a national study on women's health and lifestyles. They found that supplement users had higher intakes of all nutrients from food alone, except for fat and vitamin B12. Supplement use was associated with being vegan, vegetarian or non-meat eating, consuming more fruit and vegetables, being more physically active and having a lower alcohol intake. These findings further support the concept that those who take supplements already have healthier lifestyles than non-users and are less likely to need them.

More is not always better

Taking dietary supplements is not without risk. It is now well recognised that high doses of certain vitamins and minerals can have adverse effects in the body.

For example, high doses of vitamin A in early pregnancy can result in foetal abnormalities and this is why women planning pregnancies are advised to avoid vitamin A supplements and liver, which is naturally rich in vitamin A (DoH 1991)

Very high intakes of vitamin B6 have been linked to diseases of the nervous system (Dalton and Dalton 1987). High doses of one mineral can inhibit the absorption of others as they compete for the same absorption sites in the intestine, so high doses of calcium might reduce the absorption of iron (Cook et al 1991). Similarly, high doses of zinc might inhibit iron uptake and reduce copper status in the body (Yadrick et al 1989).

For many supplements there is little scientific evidence to support their perceived or claimed benefits, including beliefs such as the 'fact' that taking Vitamin C will ward off colds. A recent systematic review of 30 studies found that Vitamin C taken prophylactically, even at very high doses, did not reduce the incidence of the common cold (Douglas et al 1997).

It would seem that many supplements are at best unnecessary and at worst potentially harmful. Discouraging unnecessary use of supplements is, therefore, an important consideration in promoting good health.

Foods have special benefits

Scientific evidence also suggests that supplements may not be as beneficial as foods themselves. A major review on the nutritional aspects of the development of cancer for the Department of Health (1998a) found that higher intakes of fruits and vegetables were linked to a lower risk of developing certain cancers. It was thought that antioxidants such as Vitamins C, E and beta-carotene were the beneficial components in the fruit and vegetables. However, studies where supplements of Vitamins C, E and beta-carotene were given have found that they do not reduce the risk of developing various cancers (DoH 1998a). It might be that other compounds in fruit and vegetables are protective.

A similar situation can be found in relation to heart disease. Population data suggest that antioxidant Vitamins A and E can be protective against heart disease. A major study was set up in Finland to determine if supplements of these vitamins protected against future heart disease in those who had already had a major coronary event. Although non-fatal heart attacks were lower in those receiving the supplements, fatal coronary events were greater (Rapola et al 1997).

It appears that supplements of individual nutrients or even combinations of nutrients are not as effective in reducing the risk of chronic diseases, such as cancer and heart disease, as the actual fruit and vegetables themselves. Something as yet unidentified, or the combination of nutrients supplied in the fruit or vegetable, are what appear to be most beneficial.

Start with a balanced diet

Foods are likely to be the most beneficial way to get the nutrients needed. Imbalances and the adverse effects of individual micronutrients are unlikely to occur when provided from food sources. This is why, for the majority of people, vitamin and mineral supplements are not necessary. Most people can obtain all the nutrients they need from food.

All foods can contribute to a healthy diet and there is no such thing as an 'empty calorie'. Favourite foods can and should have a place in the diet. The key is to get the balance right and to eat as wide a range of foods as possible. This is because each individual food contains its own specific mix of nutrients, so the more different foods consumed, the better the overall nutritional quality of the diet. As a rough guide the diet should include;

  • Bread, rice, pasta, breakfast cereals and potatoes. These are the major source of carbohydrate. They contain a variety of vitamins and minerals. White flour is fortified with calcium and many breakfast cereals are fortified with vitamins and minerals. Sugar and sweet foods also contribute to carbohydrtae intake.
  • Meat, poultry, fish, seafood, eggs, beans and other pulses. They all provide protein and a variety of vitamins and minerals. Meat is the major source of the easily absorbed haem iron. Oily fish provides omega-3 fatty acids, thought to prevent thrombosis. Pulses are also a good source of fibre.
  • Fruits and vegetables, which are a source of fibre and antioxidants. Consuming five portions a day is thought to be protective against heart disease and cancer.
  • Milk, cheese and yogurt and foods containing them such as puddings, custard, ice cream and drinks provide protein, a range of vitamins and minerals, and in particular are a major source of calcium.
  • Spreading fats and cooking oils are a major source of fat in the diet. Poly- and mono-unsaturated oils such as sunflower and olive oil should be encouraged. Most margarines are also fortified with Vitamins A and D.

How much is enough?

In 1991 the Department of Health issued a report which gave guidance on appropriate levels of all nutrients, including vitamins and minerals, for the UK population (DoH 1991). The term Reference Nutrient Intake (RNI) was used to describe the amount of a micronutrient believed to be adequate for the prevention of deficiency and the maintenance of good health in almost all of the population. In practice, this estimate is likely to be an overestimate of requirements for the majority of the population, but dieticians and other clinicians use it as a reference point for the assessment of micronutrient intake.

When supplements are needed

There are times when vitamin and mineral supplements are a useful complement to the diet. This is when an adequate intake of nutrients cannot be achieved from the diet alone, either because the selection of foods or the ability to eat them is limited, or requirements for a particular micronutrient are increased. The following vulnerable groups are outlined in the British Dietetic Association's Position Paper on Vitamin and Mineral Supplements (BDA 1999).

  • Breast-fed infants
  • Vegans
  • Young children
  • Housebound people
  • Some Asian groups
  • Older people
  • Pre-pregnant and pregnant women
  • Alcoholics
  • Lactating women
  • Smokers

Box 1. At-risk groups who may need supplements

Full term infants

The vitamin and mineral status of breast-fed infants is dependant on the nutritional status of the mother. If her diet is good, her infant's diet will be good. However after six months, as weaning occurs, milk intake declines. It is recommended that all breast-fed infants receive Vitamin A and D supplements (DoH 1994): Vitamin A because infants are very sensitive to low intakes of Vitamin A; Vitamin D because, as they tend to be wrapped up most of the time when outside, they may not be getting enough from the action of sunlight on the skin. Infants receiving at least 500mls of reputable formula milk per day do not need supplements, as the milk is already supplemented.

Young children

Between the ages of one and five, young children might need Vitamin A and D supplements unless the diet is diverse and there is moderate exposure to sunlight. Many children are faddy eaters at this age. If a parent is anxious, it is a good idea to check that the diet is varied and balanced. It is also important to remind parents that a low-fat diet is not suitable for children under two and that they should be giving full fat milk and other dairy products.

There is also a risk of iron deficiency anaemia in young children, particularly in some Asian groups living in the UK and/or if meat or iron-fortified formula is not included in the diet. Iron supplements might be advisable.

Pre-pregnancy, pregnancy and lactation

Higher than usual intakes of folic acid prior to conception have been found to reduce the subsequent risk of neural tube defects (MRCVSG 1991). As a result of this major study, all women planning a pregnancy are encouraged to take a supplement containing 400mg folic acid. This supplement should be continued until the end of the first trimester of the pregnancy (DoH 1992).

There are increases in requirements for other micronutrients during pregnancy, but these can usually be met from the diet. If iron status is found to be low, an iron supplement is also prescribed. Women suffering from severe morning sickness may benefit from a multivitamin and mineral supplement (not to help reduce the sickness but to compensate for nutrients 'lost' as a result). Similarly a supplement might be advisable if there are any signs of poor eating habits, or if the mother is a teenager and still growing herself (Cockburn 1998).

During lactation, the increases in requirements for most vitamins and minerals can be met through diet. However, recommended Vitamin D intake for breast-feeding mothers is 10mg per day. In practice, this means that supplements are advised (DoH 1998b).

Older people and the housebound

Vitamin D status has been found to be poor in many older people (Compston 1998). The RNI for people over 65 is 10mg per day, a level that the majority of people can only achieve through the use of a supplement. Vitamin D supplements are also recommended for the housebound who are at risk of poor Vitamin D status as they are rarely exposed to sunlight. There is also widespread impairment of Vitamin B12 absorption with aging and the use of a supplement has been shown to improve B12 status more effectively than diet.


Vegans are people who eat no meat, fish, dairy products or eggs. As their diet is more limited than most, there is a risk that intake of some micronutrients may be low (Draper et al 1993). Of particular concern are calcium, iodine, Vitamin B12 and Vitamin D. Where fortified foods are not regularly consumed, the use of supplements are recommended.


Many alcoholics have poor diets and are at risk of developing overt thiamine (B1) deficiency (Iber et al 1982). A multivitamin supplement is recommended. This will not protect against the damaging effects of excessive alcohol intake, but will mitigate some of the effects of an inadequate diet combined with alcohol abuse.


Heavy smokers have an increased turnover of Vitamin C. To maintain body levels of Vitamin C, an intake of nearly twice the adult RNI is recommended. It has also been found that the diets of smokers are often less healthy than the diets of non-smokers (margetts and Jackson 1993) and the use of Vitamin C supplements may be appropriate. Again, the supplement cannot protect against the damages of smoking but might go some way to reducing the injury caused.

Others at risk

People who are on a restricted diet, such as slimmers, people who are unwell, those on exclusion diets and fussy eaters are at risk of vitamin and mineral deficiences. However, these groups should be given advice about eating a better diet, as well as supplements. Where people have a prolonged lack of appetite with weight loss, it is important to establish the cause before any advice is given, as there could be an underlying clinical condition that is causing the symptoms.

People on low incomes might consume less varied diets and this leaves them at risk of vitamin and mineral deficiencies. Although short-term use of supplements can be of benefit, the long-term solution is to help change eating habits to ensure an adequate diet. Clearly any advice needs to be in the context of their social and financial circumstances.


People are often persuaded to consume supplements following unreliable diagnosis of allergy by 'alternative' practitioners. First check that the allergy is real. Supplements are unlikely to help.

The nurse's role

Nurses must be aware that patients might have received dietary advice from a vast range of sources. Complementary therapies are very much in vogue and can be recommended by individuals, such as nutritional therapists, whose training may have lasted as little as a few weeks. None of the qualifications gained are recognised by The British Dietetic Association, which is the professional association for state registered dieticians (SRD). Nutritional therapists use a range of dietary techniques to treat diseases. They commonly offer intolerance testing, which is of dubious validity, and elimination diets, which severely restrict the choice of foods allowed. Such diets themselves can lead to dietary deficiences if followed for any length of time. Often a range of costly supplements will be prescribed, which apart from vitamins and minerals, could include natural oils, herbal extracts and other natural substances such as royal jelly.

In contrast, SRDs ahve been clinically trained and have either completed a four-year degree, or a science degree followed by a two-year post-graduate qualification in dietetics. Only SRDs are employed within the NHS and they follow official medical guidelines.


If nurses see patients whose diets are poor, they can give some basic advice on how to eat a healthy, balanced diet and reassure them that supplements are unnecessary. If a patient is in one of the 'at risk' groups, or clearly has special detary needs or circumstances, it might be beneficial to arrange for referral to the local SRD who can fully assess the diet and make any recommendations.

Implications for practice

  • It has been shown that people who regularly take supplements are often those least likely to need them.
  • For most people a varied and balanced diet provides all the nutrients needed.
  • There are a few groups in the population who are at specific risk of micronutrient deficiencies and who might need to be advised on appropriate supplements (Box 1).
  • Dietary supplements especially in high doses can be harmful.
  • Alternative dietary treatments, where costly dietary supplements are prescribed, need to be treated with caution. Some can do more harm than good.
  • If in doubt, refer to a state registered dietician for assessment.

© Carol Ottley (BSc, SRD, RPHNutr). (2000) Nursing Standard 14, 29, 42-45.


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