Diagnostics of Micronutrients
How Much Is Too Much
For a long period of time nutritional medicine did not raise many questions related to micronutrients. The main topic was to determine clinical relevant lacks in nutritional micronutrient supply, leading to classical deficiency diseases. Today we are facing far more complex problems, because we are realizing that there is a long way between a beginning suboptimal supply and the first clinical signs related to this malnutrition.
The diagnostics of micronutrient supply starts before the onset of clinical symptoms. Even a marginal lack in a certain micronutrient may cause more and more functional restrictions, which cannot be called a disease, but which are also not corresponding to optimal health.
Micronutrients have important functions which is why it can be observed that an increasing amount of people are using enriched food or nutritional supplements, some of them in very high dosage. Most supplements are taken uncontrolled, without advice or subscription from a health practitioner and without any rational background. So we also have to challenge, what health effects, either good or bad, we have to expect.
Micronutrients are involved in many biochemical processes. Vitamins like pyridoxine or riboflavin act as cofactors in enzymatic reactions, like most vitamins of the b-group. Trace elements like selenium, manganese or copper are integrative compounds of functional enzyme complexes such as superoxide dismutase (SOD) or glutathione peroxidase (GPx), which are involved in processes of redox-regulation and oxidative stress defence (fig. 1). Others act as antioxidants without activating enzymatic reactions like tocopherols or ascorbic acid. Low grade inflammatory processes are known to be part of most chronical diseases and micronutrients like selenium or omega-3-fatty acids may play a protective role in managing inflammation.
Micronutrients and Metabolism
As its name implies, there are only small quantities of micronutrients, which are supplied by our nutrition. Nevertheless they play an essential role in many biochemical pathways.
A special feature is that every single micronutrient has its defined place in the metabolism, but beyond that the overall function of a certain micronutrient is always influenced by a diverse biological network of interacting pathways. Thus, a major role of a micronutrient is its effect on interconnected processes, which are in place to ensure physical health. An example may be the regulation of inflammatory processes by fatty acids and antioxidants which are also connected to processes of oxidative stress.
If we talk about diagnostic methods there are different aspects to take into consideration:
- Concentration of micronutrients in different matrices
- Effect of micronutrients on a specific biochemical pathway
- Effect of micronutrients on health related processes
Concentration of Micronutrients
It is good practice in clinical chemistry to monitor metabolites in serum or plasma samples. Initially, the determination of micronutrient levels was also approached like this; however, these compounds may not be the right choice for many micronutrients, as the plasma levels are often regulated homeostatically. A significant drop could often only be observed in a far advanced state of deficiency.
As a result of recent studies, some target levels of plasma concentrations have been adjusted in order to ensure full functionality of a certain micronutrient, like Vitamin D. Seasonally different reference ranges have been established, because of the observed drop in plasma levels during winter season. Regarding the fact that a proper vitamin function is also necessary in winter, there are ongoing discussions about sufficient target ranges, which are significantly higher than before.
Because of the insufficient significance of the plasma concentration of certain micronutrients, some determinations may be done with corresponding bioactive metabolites instead. The determination of holotranscobalamine 2 for example provides a far better predication for the supply of Vitamin B12 than the determination of Vitamin B12 itself.
Besides plasma, there are a wide range of different matrices, like whole blood, erythrocytes, urine excretion or dermal appendage like hair or nails where micronutrient concentrations have been measured. It must be ensured that the micronutrient concentration in any matrix is able to answer the respective diagnostic questions. Maybe there are higher concentrations of certain micronutrients to find, but it has to be ensured, that there is a clear coherence with the exposition to micronutrient supply and that the pre-analytical requirements can be kept under clinical routine conditions.
Functional Micronutrient Parameters
One possibility to analyze the individual effect of a micronutrient on biochemical processes is to look at the enzyme activities, which are directly influenced by the presence of the corresponding micronutrient. This can be done by measuring enzyme activities directly or by measuring biomarkers that accumulate, if the subsequent pathway is restricted due to the lack of the activating micronutrient. A well known example for this methodology is the determination of methylmalonic acid, which can only be further processed in presence of vitamin B12. So an accumulation of methylmalonic acid expresses a functional lack of B12.
Due to different genetic conditions the same amount of a certain micronutrient is not necessarily linked to the same metabolic function. The human genome shows significant variation and up to date about 38 million single nucleotide polymorphisms (SNP's), 1.4 million short insertions and more than 14000 larger deletions were detected. Many of them have an effect on metabolic pathways and so the "one diet fits all" approach is no longer applicable.
Micronutrient Health Parameters
Micronutrient-dependent pathways are involved in maintenance of optimal health and thus, micronutrients are able to influence such processes. Especially, if someone considers taking nutritional supplements, clinical relevant parameters can be chosen to monitor micronutrient action. However, supplementation should not only aim to bring plasma concentrations into a defined reference range but should also be verified by focussing on (additional) health parameters.
Inflammatory processes for example can be influenced by the relation of long chain omega-3 to omega-6 fatty acids, namely eicosapentaenic acid (EPA) to arachidonic acid (AA) which are precursors of prostaglandins. If a supplementation is able to shift this ratio in the direction to EPA, the influence of this intervention can be monitored by markers of inflammation, such as high levels of C-reactive protein (CRP) (fig. 2).
The questions in the field of micronutrient diagnostics are manifold and for every task a proper selection of biomarkers, which allow answering these questions, needs to be done. Mostly this selection will be a combination of concentration and functionality of the micronutrient of interest.
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