Micronutrients: definition, role and dietary sources

What role do micronutrients play?

A micronutrient is a nutrient with no energy value (that does not provide any calories), which is present in small amounts in the body, yet is nonetheless essential for life (1). Depending on its properties, a micronutrient can play a role in growth, metabolism, immunity or reproduction.

Almost all micronutrients are provided directly by food, the body being largely unable to synthesise them. Our daily requirements remain relatively low, in the region of a few tens of mcg or mg, though intake needs to be consistent in order to maintain the integrity of the body.

Micronutrients and macronutrients: not to be confused

Macronutrient: definition

Macronutrients differ from micronutrients not only in their clear predominance in our daily nutrient intake (which amounts to several tens of grams), but also in their ability to provide energy(2). There are three types of macronutrient: carbohydrates, protein and fats.

Role of macronutrients

Carbohydrates are the preferred fuel of cells (3). Protein is, amongst others, the ‘cement’ of living organisms, providing the body with a structural framework and playing a role in maintaining muscle mass (4). Fats are a component of cell membranes and are also used by the body as a source of energy (5).

Essential micronutrients: what are they?

Vitamins

There are 13 vitamins, divided into two groups: water-soluble and fat-soluble (6).

The water-soluble vitamins include vitamin C (which contributes to normal collagen production and immune system function) as well as all the B group vitamins involved in various metabolic functions (7-8).

The fat-soluble group includes vitamin A (normal vision), vitamin E (protection against oxidative stress), vitamin K (normal blood-clotting) and vitamin D (9-11). Vitamin D deficiency is widespread in many parts of the world due to there being few dietary sources and the fact that many people have low exposure to the sun in winter (12).

Vitamin deficiencies manifest in diverse clinical symptoms with consequences for health of varying severity. Expectant mothers need to be particularly careful to ensure their increased needs for vitamin B9 are met, as it contributes to normal growth of the foetus (13). And vegans, who have excluded meat and animal-source foods from their diet, are at risk of vitamin B12 deficiency (14).

Minerals

Minerals are a group of inorganic elements which are necessary for maintaining functions in the body. They include calcium, phosphorus, potassium, sodium and magnesium (15).

Involved in many biochemical reactions, minerals play a role in a wide variety of areas such as bone consolidation, regulation ofbodily fluids, muscle contraction, transmission of nerve impulses and mental balance(16-17).

It’s worth noting that certain factors tend to accelerate mineral loss: stress (lower magnesium levels), kidney disease and/or diuretic treatments (loss of potassium), advancing age or intestinal malabsorption (impaired calcium uptake) (18-20)…

Trace elements

Compared with minerals, trace elements are only required by the body in very small amounts (measurable in micrograms). They primarily encompass iron, zinc, copper, selenium, manganese, iodine, chromium, cobalt, fluoride and molybdenum (21).

Though we need very little of them, trace elements are nonetheless crucial. For example, iron contributes to normal red blood cell and haemoglobin formation, zinc helps maintain healthy skin, and selenium is important for spermatogenesis and thyroid function(22-24).

Lack of iron remains the most common trace element deficiency across the world. Menstruating and pregnant women are particularly affected as are the elderly and vegetarians. Persistent deficiency can lead to anaemia, which manifests in fatigue, muscle weakness and shortness of breath (25).

Essential fatty acids

Fatty acids are the building blocks of large fat molecules. Those termed ‘essential’, are the ones the body cannot produce itself but which are absolutely vital (26-27).

There are two main categories of essential fatty acids:

• omega-6 polyunsaturated fatty acids, the essential precursor of which is linoleic acid (LA).
• omega-3 polyunsaturated fatty acids, the essential precursor of which is alpha-linolenic acid (ALA).

Found exclusively in plant-source foods (flax, rapeseed, nuts …), ALA theoretically enables the body to synthesise eicosapentaenoic acid (EPA) and docosahexaenoic acid (DHA). Protectors of cardiovascular health, both support normal cardiac function and help maintain normal blood pressure(28).

However, this conversion is rarely sufficient to meet the body’s needs (29). EPA and DHA are therefore classed as semi-essential and for the most part, need to be provided by the diet, in particular from oily fish (sardines, mackerel, anchovies…) (30).

Essential amino acids

In the same way that fatty acids make up lipids, amino acids determine the structure of protein.

Amino acids are therefore involved in a wide variety of biological processes, from muscle tissue renewal to neurotransmitter synthesis and antibody production.

Of the 20 existing amino acids, only 9 are considered essential: leucine, isoleucine, valine, lysine, phenylalanine, threonine, tryptophan and histidine (31).

Animal protein sources (meat, poultry, eggs …) contain all the essential amino acids (32). Pulses and grains, on the other hand, are normally lacking in methionine and lysine, so vegetarians would benefit from combining them to obtain protein complementarity.

Micronutrients: foods to prioritise

To benefit from a wide range of micronutrients and achieve the recommended daily amounts set by health authorities, you need to eat a varied, balanced diet, with as few processed foods as possible.

Vitamins are more or less present in all food categories. Vitamin A alone, for example, is found in yellow-orange fruits and vegetables as well as in offal and dairy products (33)!

Mineral-wise, wholegrain rice, nuts and seeds, pulses and darkchocolate are the best sources of magnesium (34). Calcium is not only found in milk: it’s also in sardines, almonds, and cabbage (35).

In terms of trace elements, oysters are the no. 1 source of zinc along with seafood and red meat (36). The latter is also a good source of iron, as is black pudding and cocoa (37). There’s a significant amount of selenium in fish, calves’ liver, wholemeal bread and Brazil nuts (38).