Table of Contents

  • Biochemical indicators of dietary nutrient intake are called biomarkers. They may be used in clinical settings to assess deficiency or excess of nutrients like vitamin C and D. In nutritional epidemiology estimation of the dietary intake of foods and nutrients is done in order to classify subjects according to their nutrient intake and relate it to disease. Like for intake assessment methods there are pros and cons to be aware of when using biomarkers to estimate nutrient intake. These include the available tissue, nutrient metabolism, chemical method for analysis, specimen collection and storage and diurnal and biological variation.

  • My intension in this brief review is to consider why biomarkers of nutrient intake are useful and to explore some criteria for robust biomarkers; finally the potential for emerging biomarkers will be considered.

  • In nutritional epidemiology we are both interested in nutrient intake as well as the intake of whole foods because whole foods might provide bioactive factors in addition to the already known vitamins, minerals and phytonutrients.

  • Iodine deficiency is a large problem worldwide and iodine deficiency still exist in the Nordic countries especially in Denmark. The most obvious manifestation of iodine deficiency is goitre which is an enlarged thyroid gland. In addition to goitre iodine deficiency diseases include a spectrum of conditions that vary in severity. The most severe of these, cretinism with mental deficiency, retarded physical development e.g., does not exist in the Nordic countries. However, toxic and non-toxic goitre is seen especially in the elderly.

  • Vitamins are usually compounds that the body is not able to synthesize. However, vitamin D is unique since the body is able to synthesize an active vitamin D compound through sunshine. Due to this fact, dietary intake calculated by linking data from Food Composition Tables and Dietary Surveys do not reflect the amount of vitamin D the body has access to.

  • The necessity of vitamin C (ascorbic acid) for human health is firmly established. As humans are not able to synthesize ascorbic acid, they are dependent on their dietary intake. The dietary sources of vitamin C are fruits and vegetables, especially in uncooked forms. The historical discovery of the beneficial effects of fruits as food dates back to the Middle Ages. Scurvy was common among sailors during the long sea expeditions of the 15th and 16th centuries. The sailors suffered from symptoms of scurvy: capillary hemorrhages, bleeding gums and loosening of teeth, reduced rate of wound healing, depression and fatigue. Vasco da Gama, for example, lost about 100 of his 160 seamen in his India passage between the years 1497-1499. As late as 1740, the British admiral Anson lost five of his six ships and 1165 of 1500 seamen before reaching the coast of South America. Also during wars in the 19th century, when food shortage was acute, scurvy was a problem.

  • More than 20 specific selenocysteine-containing selenoproteins have now been identified in animal tissue (Behne, Kyriakopoulos, 2001; Kryukov et al. 2003), but the concentrations and distribution of selenoproteins in different tissues are not well known. In human plasma, extracellular glutathione peroxidase (GSHPx) and selenoprotein P have been demonstrated (Takahashi, Cohen, 1986; Åkesson et al., 1994; Huang 1996; Persson-Moschos, 2000).

  • The fatty acid composition of our diet will directly affect the lipid composition of most tissues in the human body including all cell membranes, circulating lipoprotein lipids and storage fat. The fatty acid composition of the body tissues has profound effects on a number of vital functions such as gene expression, metabolic signalling, eicosanoid production, membrane properties and energy expenditure.

  • Worldwide, iron deficiency (ID) is the most common micronutrient deficiency. That is because certain population groups have high iron requirements, but insufficient iron intake or absorption to meet their needs. The relative iron requirement is greatest in infants and young children (aged 6-24 months) and adolescents (aged 12-16 years), which is explained by the food intake and rapid growth rate in these age groups.

  • Flavonoids are polyphenolic compounds obtained from various fruits and vegetables. To date, over 6000 flavonoids have been identified, however, a much smaller number are important from a dietary point of view. One of the most studied flavonoids is quercetin, which is a compound that exhibits a wide range of different bioactivities in vitro. Quercetin is obtained from various fruits and vegetables, with onions, tea, and berries being particularly good sources. The flavanones hesperetin and naringenin are among the most important flavonoids from a quantitative intake point of view. Their intake is high because of the common use of citrus fruits and juices, which are their main dietary sources. For a recent review on the flavonoids see ref. 1. We developed analytical methods for the analysis of quercetin, hesperetin and naringenin in human serum (2) and studied their bioavailability. We also investigated their use as biomarkers of intake.

  • Epidemiological studies have provided evidence that a high intake of fruits and vegetables is associated with a decreased risk of heart disease and some human cancers [1-3]. Current dietary assessment methods used in epidemiological studies are associated with random and systematic measurement errors, and therefore more objective ways are needed to more accurately assess the intake of foods important to human health. Reliable biological makers for the intake of vegetables or fruits are needed to get a better insight in the health effects of vegetables and fruits.

  • Main goals in population health surveys are to monitor trends in disease risk factors in the general public and risk groups as well as to assess nutrient intake. Nutritional epidemiology deals with associations between nutrients and disease risk. Traditionally the 24-hour recall in combination with a food frequency questionnaire to collect food consumption data has proven to be a cost-benefit method in most instances. There are, however, nutrients for which dietary methods are less good. In these instances biomarkers may be a better or alternative approach. Biomarkers are not without certain limitations. One of the basic requirements of a biomarker is that it reflects the intake of a nutrient. Some do quite accurately, like beta-carotene, but in most instances the relationship is limited to some extent by homeostasis, metabolism, age, gender and nutrient interactions.