expert opinion

What Vitamins Can and Cannot Do

May 1, 2009

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Prof. Dr. med. Hans K Biesalski, Institute for Biological Chemistry and Nutritional Science, University of Hohenheim, Stuttgart, Germany

“Every micronutrient unfolds a specific effect in the human organism. These effects are complex, sometimes dose-dependent and can vary from one type of tissue or organ to another; not all the configurations are known to us. Interactions with other substances make the situation even more complicated. The function of a micronutrient only becomes evident when the deficit of a single micronutrient over a length of time leads to a typical deficiency condition. Conversely, a deficiency condition can indicate the need for an increased supply of certain nutrients to balance the deficit.

Even today it is not easy to determine a lack of micronutrients: while some obvious and well-established deficiency diseases, such as scurvy due to a lack of vitamin C, have almost disappeared in industrialized countries, only around a third of the micronutrients known today are associated with deficiency diseases with typical signs which can be detected by an experienced physician. The majority of the others have no known characteristic signs associated with them. But an undiscovered undersupply or deficit could still cause initially undetectable damage which could form the basis for severe illnesses which only develop years later. For antioxidants such as vitamin C, vitamin E and beta-carotene there is already good evidence to indicate that an inadequate diet or elevated requirements can often lead to atherosclerosis, cancer, stroke and other diseases.

It is, however, a mistake to believe that we just need to supplement the single micronutrient for the risk of such diseases to be reduced. The best preventive measure is a diverse and balanced diet, which will contain many of the substances important to the body. Please note the use of the term “preventive”. According to epidemiological studies, a diet rich in vitamins can indeed prevent diseases, but is not enough to cure them or even significantly improve their course.

Confusion is further exacerbated by statistical analyses of many divergent studies: such ‘ meta-analyses ’ frequently conclude that the administration of vitamins is pointless if not actually harmful (e.g. life-shortening). Unfortunately, these publications or this type of conclusion have proved to be methodologically unsound, because they do not differentiate between primary prevention and secondary prevention in the individual studies; thus possible health-preventive properties of vitamins in healthy persons and potentially therapeutic effects in the sick are mixed together, leading to a distortion of the results. If a distinction is made between primary and secondary prevention, we come to a different result: even high doses of antioxidants do not have a life-shortening effect, either in healthy persons or in the sick.

However, the same applies here: multivitamin preparations can neither compensate for the consequences of an unhealthy lifestyle which contributed to an illness, nor can they replace the many other effects of a healthy diet. Moreover, micronutrients ingested in the form of food supplements only have an effect when they compensate for a previously existing undersupply. This deficit may be caused by an inadequate diet, but may also be the result of elevated requirements or genetic preconditions affecting metabolism. How much the individual actually needs then is not certain. For long-term administration the amount should not exceed three times that recommended by expert organizations as a rule, even if high doses are well tolerated in the short term.

The question remains whether micronutrient deficits in developed countries are not in fact rare. And the answer is no. In recent years several risk groups have been identified. A prominent case is the recently published ‘Nationale Verzehrsstudie II’ covering food consumption in Germany, which contained worrying statistics. Thus the intake of vitamin D, calcium and vitamin B9 (folic acid) fell short of the recommendations in almost 100% of the population, and for vitamin E it was still 50% short. The list of risk groups meanwhile includes the majority of the population – from the aged and socially deprived groups to pregnant women and cancer patients, the overweight and those on a diet, the extremely hard-working and top athletes, and vegans. A closer inspection of the statistics unfortunately reveals that the balanced diet is a rare commodity.”

(See also Principles - The complexity of micronutrient research)