Dietary supplements: what are the safe levels?

The formulation of vitamin and mineral supplements has been self-regulated in the UK since 1985 by the Health Food Manufacturers' Association (HFMA). A decade later the European Federation of Associations of Health Product Manufacturers (EHPM) published recommendations for self-selection of vitamin and mineral supplements by consumers.1 In this publication, the term 'upper safe level' was used to define the greatest daily quantity of a supplement that could be consumed by an adult without giving rise to a possible adverse effect. It was not a recommendation for consumption—it was a guideline for safe use.

Also in 1995, the US and UK branches of the Council for Responsible Nutrition (CRN) began an international collaboration on the scientific assessment of risk.2 They made risk management recommendations regarding the role vitamin and mineral supplementation could play in the improvement of health worldwide.3Around this time, the Food and Nutrition Board in the US, the Food Standards Agency in the UK, and the European Union's Scientific Committee for Food (now called the European Food Safety Authority) also began reviewing the consumption of vitamin and mineral supplements.

American studies have been the most wide-ranging, reviewing not only safety but also requirements to prevent the classical deficiency diseases and, for the first time, assessing the dietary intakes of micronutrients associated with improved health, a concept of optimising health through diet.4,5,6,7 European studies have more often been confined to scientific risk assessment of micronutrient consumption. Their conclusions are currently available on official Web sites.8,9 Encouragingly, most of both governmental and industy studies' findings concur, which should induce a high degree of confidence in the consuming public.

Risk and safety
It is not possible to guarantee safety for all individuals in all circumstances. A safe road is one on which an accident is unlikely to occur, but an accident-proof road is beyond the possible. Similarly with foods: a sample will give an indication of, for example, the presence of a poisoning bacteria. Assumptions can then be made about the batch of food from which the sample came. This process is termed 'risk assessment.' Once this kind of assessment has been performed, it is then the responsibility of managers to interpret the scientists' conclusions in the context of the market for which the product is intended.

There are thus two stages in assessing the safety of a product before it is released for sale to the public: the scientific stage of 'risk assessment' and the subsequent management stage of 'risk management.'

The principles of risk assessment and risk management are the same for nutritional supplements as for all foods—but there is a difference in the detail. Supplements in tablet or capsule form have so little bulk that there is no control over the amounts consumed from the natural process of satisfying hunger. Consequently, guidelines are necessary to indicate what might be the maximum levels that can be consumed without harm on a daily basis over a lifetime.

Water-soluble vitamins, such as C and the B group, are not stored in the body, and for these there is no problem with reference to the period of consumption, but there is another consideration. If an adverse effect is the consequence of a relatively long period of consumption, several years for example, then there may be cause to limit the consumption of the product, not necessarily to its maximum amount in a tablet or capsule but by limiting the period over which it may be consumed.

It is not possible to guarantee safety for all individuals in all circumstances. A safe road is one on which an accident is unlikely to occur, but an accident-proof road is beyond the possible
Vitamin B6 presents this challenge to the regulator. It has a record of successful intermittent use over many years. There is also evidence of toxicity at high dietary intakes and further evidence that the development of the adverse effect (neurological damage) is cumulative. The regulatory problem is thus to relate an upper safe level for consumption to the frequency of consumption. In the case of vitamin B6, it would appear that daily consumption for one week in four at levels up to 200mg is both effective and safe, but there is no scientific proof. The risk manager must therefore evaluate evidence using market knowledge to interpret the limited scientific data available from the risk assessment. His goal is to meet the dual consumer requirement of safety and continued availability of a relatively high-potency product for regular but intermittent use.

Risk assessment and risk management
The B6 dilemma illustrates the difference between risk assessment and risk management. The starting point for ensuring safety is a risk assessment of the micronutrient obtained by a review of the scientific literature. Human studies are preferred. Animal data must be interpreted for the human circumstance. Typically, an upper safe level obtained from animal data is divided by 10 unless there is compelling evidence to demonstrate that human and test animal sensitivity are essentially similar.

It is also desirable for the risk assessment to be made by directly reviewing the consequences of consumption of the micronutrient supplements in addition to an otherwise complete diet and for the sample and length of study to be as great as possible. Any groups of individuals who might be unusually sensitive to the vitamin or trace mineral should also be identified. Pregnant women and nursing mothers are important groups to consider, but there may be other, less prominent, groups that could be at risk and whose presence in a risk category may only become apparent from a study of the scientific literature.

The conclusion of the scientific risk assessment will provide a highest safe daily consumption level as a supplement by the majority of the adult population, together with an itemisation of and label warnings directed to any minority groups that might be expected to be sensitive to it.

There are occasions when it might not be possible to provide a recommendation based on the scientific data. For example, there may never have been recorded an experience of an adverse effect, which is the case with B vitamins. In such a situation, the highest scientifically acceptable recorded consumption has to provide the baseline guide with the understanding that higher levels also may be, or not be, without adverse effect. In other situations, the scientific data are simply inadequate, either because they are of low quality, as with vitamin B6, or because studies have not been undertaken at all.

In most cases, the risk manager has to focus attention on the possibility of small but sensitive groups and consider whether they can be protected by clear product labelling or by other means. In such considerations, the risk manager must recognise that the scientific assessment has already taken account of the quality of the scientific literature and has applied caution to its interpretation.

Hence, the regulator is unlikely to find it necessary to invoke a further 'precautionary principle.' Indeed, the object of the scientific risk assessment is to provide an objective assessment and thereby define a rationale for an upper safe level for the general public. The risk manager's task is to take account of any minority group that is potentially at risk according to the scientific risk assessment, and advise formulation of regulations to protect them from adverse events whilst providing the scientifically determined 'upper safe levels' for all others.

Derek H Shrimpton is scientific advisor to the European Federation of Associations of Health Product Manufacturers.
Email: [email protected]


1. Shrimpton DH. Essential Nutrients in Supplements. Euro Health Prod Mfg. Assn, Office of the President, PO Box 223A, Surrey (UK); Thames Ditton, 1995.

2. Hathcock JN. Vitamin and mineral safety. Washington, D.C.; Council for Responsible Nutrition 19973. Vitamins and minerals: a scientific evaluation of the range of safe intakes. Council for Responsible Nutrition, 63 Hampton Court Way, Thames Ditton, Surrey KT7 0LT (UK), 1997.

3. Richardson DP. Nutrition in transition: the role of micronutrients. International Alliance of Dietary/Food Supplement Associations, (IADSA) 50, Rue de l'Association B-1000, Brussels (Belgium).

4. Dietary reference intakes for: calcium phosphorus, magnesium, vitamin D and fluoride. Washington DC; Food and Nutrition Board, National Academy Press, 1997.

5. Dietary reference intakes for: B-vitamins and choline. 2000, Ibid.

6. Dietary reference intakes for: vitamins C & E, selenium & carotenoids. 2000, Ibid.

7. Applications in dietary assessment. 2001, Ibid.

8. Safe Upper Levels for Vitamins and Minerals: Report of the Expert Group on Vitamins and Minerals 2003, Website:

9. Opinions of the Scientific Committee for Food on tolerable upper intake levels, Web site:

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