What do micronutrients do?
Micronutrients participate as co-factors in specific enzymes (biological catalysts). A dietary deficiency of any one of them may compromise the vital processes in which they are involved. Whether micronutrients are soluble in water or fat affects how long they are stored in the body; fat-soluble micronutrients (vitamins D and E) are sequestered in fat deposits and tend to be retained better than the water-soluble factors. Physiological systems are often vitally dependent on a number of micronutrients as follows:
1 Genome maintenance
Many micronutrients are involved in synthesis and repair of DNA. Any failure of genome maintenance can cause mutations with a variety of consequences that include programmed cell death, the start of a malignancy or neurodegenerative disease or initiation of ageing.
2 Protection of cells from oxidative stress
A steady trickle of powerful oxidising agents (sometimes called oxidants, or free radicals) is produced by the energy-generating machinery of cells, anti-microbial defences and inflammation. These can damage other cell components by oxidative reactions (usually known as oxidative stress). The capacity to neutralise these oxidants is a crucial part of the maintenance arrangements of cells; this includes enzymatic anti-oxidants and a number of micronutrient anti-oxidants (vitamin C and E, selenium and lipoic acid). Premature age-related diseases, including cancer, are a likely consequence of ineffective anti-oxidant activity.
3 Defences against microbes
Vitamin A has a vital role in maintaining epithelial barriers to infection. Vitamin D, in addition to its many other functions, is a key player in the innate immune system — the front-line defence that produces anti-microbial chemicals in “barrier” tissues . Vitamin D is a key activator of the receptors that recognise invading microbes and deficiency compromises this function.
4 Energy generation
Vitamins B1-B7 and co-enzyme Q are co-factors for enzymes that release energy from glucose or in the energy-generating system of the mitochondrion. The decline in mitochondrial activity that accompanies the ageing process may be accelerated by deficiencies of iron, zinc, magnesium, manganese, vitamin B5 or vitamin B7. Deficiencies of any of these may affect the iron-containing proteins of mitochondria and provoke a leakage of oxidants.
5 The nervous system
Micronutrients are involved in almost every aspect of cell biology. Any deficiency is likely to compromise neural function throughout the life cycle and could have consequences that affect early development or the onset of age-related neurodegenerative diseases. There is widespread suspicion amongst biologists that relatively small deficits could affect behaviour without any overt pathology. Much more research is necessary. Work so far has focused on severe deficiencies, which have been linked to pathological conditions. For example:
- Iodine is needed to make thyroid hormone, which is required for brain development during fetal and early postnatal life. Severe deficiency of this micronutrient causes irreversible brain damage known as cretinism — the most common preventable cause of brain damage in the world today. The nutrient is normally present in plant and animal tissues but the soil in high-rainfall regions remote from the sea tends to become depleted. The problem is easily solved in principle by ingesting iodised salt although concurrent iron deficiency may exacerbate the problem.
- A triple deficiency of Vitamins B6, B9 and B12 causes an elevation of homocysteine in serum that is regarded as a risk factor for increased atrophy of the brain and possibly for cognitive impairment and Alzheimer’s disease. Recent trials suggest that dietary supplements of the three micronutrients substantially reduce brain atrophy.
- Pregnant women with significant deficiencies of Vitamins B9 (folate) and B12 are at risk of having babies that develop Spina bifida, a disorder in which embryonic neural tube fails to close properly. Even if this is closed successfully by surgery there is a significant chance of irreversible neurological damage.
- Docosahexaenoic acid (DHA), the long chain omega-3 fat is concentrated specifically in the cell membranes of the grey matter of the brain and the retina. A deficiency of DHA is associated with increased risk of poor visual and neural development in infants while a decline in DHA in late middle age may indicate increased risk of cognitive decline and dementia.
- Some studies suggest that a deficit of DHA damages the function of the retina and brain.