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Although there is copious scientific evidence to support the importance of micronutrients such as vitamins and carotenoids for health, studies investigating the positive effects of micronutrients on health sometimes come to conclusions that are less clear than expected or even contradict expectations. This is actually not surprising, because the relationships between diet, health and disease are extremely complex and are affected by many factors. It is correspondingly difficult to verify and influence these relationships.
In developing countries, where people often do not have an adequate supply of essential nutrients, supplementation, for example, has demonstrated marked success in preventing deficiency-related diseases. However, in industrialized countries many supplementation studies fail in their attempt to reduce the risk of diseases of civilization such as cardiovascular diseases, diabetes and cancer – all of which are linked to many other lifestyle factors than diet. After all, an adequate supply of micronutrients is only one of the prerequisites for maintaining health. Others include a generally balanced diet and regular exercise. So when, for example, a study reports that vitamins taken by a group of people for a specific length of time at a specific dose show no clear (“significant”) reduction in cancer risk, this does not indicate (“prove”) that these vitamins have no positive effect on the risk of developing cancer. In this group of people, it does, however, indicate that in this group of people cancer cannot be prevented solely by taking vitamins.
Apart from this complexity, a lack of suitable methods of investigation makes it difficult to find evidence for the effects of micronutrients in the human body. Currently micronutrients are being tested against placebos in investigations into the prevention and treatment of many diverse diseases, in the same way as drugs are tested (see "Quality of studies”). Such studies compare, for example, the frequency of the incidence of certain diseases in two trial groups. Strictly speaking one group of volunteers should regularly take a specific micronutrient while a control group takes a placebo and avoids the micronutrient. However, since unlike medicines it is not possible to prevent the intake of micronutrients in food, i.e. everyone consumes some micronutrients, there is in fact no proper control group. Moreover, the lifestyles and micronutrient consumptions of the volunteers differ. A direct comparison of, for example, “frequency of incidence of heart disease in people taking vitamins and people not taking vitamins” is thus impossible in practice.
The research methods available to micronutrient researchers to reduce the risk of disease therefore deliver results which are seldom unambiguous and often only reflect part of the state of affairs. The fact remains that an adequate intake of vitamins and other micronutrients is absolutely essential for all chemical processes in the body and for healthy living in general. But micronutrients are not “magic bullets”. They cannot replace all other health-promoting measures or compensate for an unhealthy lifestyle.
Apart from the complexity of the relationships between micronutrients and health, it is the lack of suitable research methods which makes it so difficult to find evidence of the effect of micronutrients in reducing the risk of disease, for example. The validity of scientific results depends on the quality and type of the studies which have generated them. While properly executed experimental studies can provide strong evidence or even proof, scientific publications based on inaccurate methodology, results and conclusions create at best hypotheses which need to be tested in further experiments.
Identifying the really informative studies among the many scientific publications is not an easy task, since their quality depends on many different factors. Results may be distorted when, for instance, studies are used to generate data “retrospectively”, i.e. when study participants are asked to give details about dietary habits, perhaps looking back over a period of years. The volunteers may not have accurate recall and their information may be of limited reliability. Further, so-called “meta-analyses” may distort results by mixing data from studies of varying quality and with differing objectives. Thus it is misleading when results of studies in which healthy subjects were given micronutrients preventively to reduce the risk of disease are combined with results from studies in which volunteers already suffering from the disease were given large doses of micronutrients to treat the condition.
The results of “randomized controlled studies” (RCTs) which are the method of choice for testing medicines, are generally regarded as more valuable than the results of other types of study. But even RCTs are not uncontroversial in micronutrient research. Researchers make the point that while it may be possible to compare the effect of one medicine with that of another which contains no active ingredient (placebo), this method cannot be applied to micronutrients or nutrients in general. Since micronutrients are vital to our survival and everyone consumes them to some extent, in actual fact no “control group" (placebo group) consuming no micronutrients at all can exist. The establishment of such a control group under experimental conditions would be unethical anyway. Furthermore, while it is easy to monitor intake of a medicine, the same cannot be said of the daily food consumption of volunteers and the potential effects of their individual ways of life. According to the experts, there is currently no really suitable method of analyzing the effectiveness of micronutrients.
Planning and executing valid studies on the efficacy of micronutrients, especially to prevent multifactorial diseases such as cardiovascular diseases, is therefore a complicated matter and depends on many parameters. Thus a study may not lead to the expected outcomes for many reasons, including inadequate duration of micronutrient intake, less than optimum dosages, deficiencies in the monitoring of micronutrient blood levels, a lack of good clinical methods to analyze the severity of the disease, weaknesses in the selection of volunteers and compliance with diet plans, as well as erroneous timing.
Micronutrients are absolutely essential to health and necessary to many metabolic processes. A lack of vitamins, for example, can lead to diverse minor to severe health problems. The severity of a problem depends on several variable factors such as age, sex, general health (e.g. chronic diseases) and individual circumstances (e.g. pregnancy). A lack of the most important vitamins during the first months of life can have dire and permanent consequences.
There are various forms of micronutrient deficit, from “insufficiency” to severe “deficiency”. Whereas as a rule a severe deficiency will cause obvious clinical signs and symptoms, the consequences of insufficiency may not be immediately apparent. Nevertheless, in the long term an insufficiency may heighten the risk of chronic diseases such as cardiovascular diseases or cancer. At present it is not clear what the “optimal” intakes of micronutrients are and at which point one can speak of a “less than optimal” supply. The debate about adequate intakes of vitamins and substantiation of their health effects is a case in point.
Micronutrient deficiencies and insufficiencies affect not only people who do not have access to these nutrients or who cannot afford them, but also those who are overweight or obese. Many nutrition studies confirm that vitamin deficiency occurs in the wealthy societies of industrialized nations, too. Recently implemented health and nutrition surveys have shown that many people in Europe and the United States consume fewer than the recommended vitamins, increasing their risk of vitamin-deficiency-related disease. This applies above all to women of reproductive age, pregnant women, children and young people, older people, people on a weight-loss diet, socioeconomically deprived groups, alcoholics and smokers. Diet-related health problems are a global phenomenon which is being combated on the national level by daily intake recommendations for micronutrients.
Our bodies cannot produce vitamins, or only in insufficient amounts. We are therefore reliant on consuming vitamins with our food. A so-called “balanced diet”, with a varied mixture of fruit and vegetables, for example, ensures a rich supply of vitamins and minerals which is essential to health. The amount of fruit and vegetables which should be consumed every day depends on age, sex and health status, among other things. At present it is not clear what the “optimal” intakes of micronutrients are and from what point one can say the supply is “less than optimal”.
Many experts recommend that we eat five daily portions or 500 to 650 grams of fruit and vegetables. Nutrition surveys in industrialized countries show that people consume on average less than three portions a day. Some people evidently find it more difficult to adhere to the recommendations than others. Older people sometimes find it difficult to eat enough food or to prepare proper meals, and thus to ensure an adequate intake of micronutrients. Young people, on the other hand, tend to live a fast-paced life characterized by a diet poor in vegetables, fruit and whole-grain products. People limiting their food intake to lose weight or maintain their current weight are also prone to consuming insufficient amounts of micronutrients. For these reasons many people use foodstuffs enriched with micronutrients or dietary supplements to fill the “gaps” in their diet.
The ultimate goal is to aim at and promote a healthy diet rich in micronutrients, especially for those whose eating habits hinder adequate intake.
An adequate supply of micronutrients is absolutely necessary for our health. The amounts needed differ from one individual to another, depending on age, sex, state of health and lifestyle, among other things. The consequences of an inadequate supply are not always immediately apparent, but in the long term can contribute to the development of chronic diseases such as cardiovascular diseases or cancer. The “ideal” intakes of micronutrients to provide “maximum” health benefits are a matter of debate among nutrition experts, as is the question, at which point can we say intake is "less than ideal".
Nutrition experts have established recommendations for daily amounts of micronutrients as “Recommended Daily Allowances (RDA)”, for example, which are supposed to cover the requirements of an entire healthy population of the same age and sex in comparable life situations (see also "Recommendations”). Some researchers criticize that the current recommendations are mainly based on the average consumption of healthy persons and that additional amounts which could represent health benefits are neglected.
Since the effects and side-effects of micronutrients are dose-dependent, a continuous intake of very high doses of some micronutrients over a long period could be harmful to health. For this reason European and US health authorities have defined “Tolerable Upper Intake Levels (ULs)” for some vitamins and minerals. These levels are based on the highest daily intakes which are not expected to have negative effects on health even with long-term consumption.
If you have questions regarding recommended intakes for micronutrients in the diet or as food supplements, ask your nutritionist, dietician or doctor.
Many people consume foodstuffs fortified with micronutrients or dietary supplements to close the “gaps” in their diet and meet their individual needs. Most of these products contain vitamins and other micronutrients (alone or in combination) which have been added in their isolated form or manufactured using chemical processes. There is an ongoing debate about whether isolated vitamins and those occurring in fruit and vegetables have comparable effects.
Some people say that the vitamins in fortified foods and dietary supplements do not fulfill the same functions in the body as those from fruit and vegetables, because they are present in their isolated form and may be missing certain components only present in whole fruits, for example. These cofactors (e.g. bioflavonoids) may improve the bioavailability of certain vitamins.
Others argue that there is no reason why isolated vitamins should be less effective, because their structures are “nature-identical”. They claim the effect of the individual substances depends on their molecular structure and dosage, rather than on whether they are of natural or synthetic origin. Moreover, isolated vitamins are often taken up better by the body, and do not come with the harmful substances (e.g. pesticides) present in many natural sources.
Since the relationships between micronutrients and health are very complex and the available methods of research are not adequate to provide clear evidence, at present we have theories but no definitive answers.
But it is important to note that “natural” components of food are not necessarily gentler on the system or better for health. Many natural components of food are active ingredients with strong biological actions. Their role in the diet and their safety have not yet been finally investigated. Some of the most poisonous substances are of natural origin.
If you have questions regarding micronutrients in the diet or as food supplements, consult your nutritionist, dietician or doctor.