Micronutrients
Micronutrients are substances such as vitamins and minerals that are necessary dietary components. Although needed in only small amounts, they are essential for health and wellbeing. The consequences of their absence are severe, impacting in particular on children’s physical growth, mental development and immune function.
Kiwifruit
Food provides macronutrients and micronutrients. Kiwifruit is a good source of vitamin C – a micronutrient that is essential for health and wellbeing and the kiwifruit enzymes help digestion.
How much do we need?
Unlike macronutrients, which are needed in tens to hundreds of grams per day, micronutrient requirements range from several micrograms to several grams.
For example, the recommended daily intake for teenagers of the mineral calcium is about 1.3g, for vitamin C, it is 40mg, and for the trace mineral chromium, the figure is 21–35μg.
The relationship between a gram, milligram and microgram
This visual representation of the relationship between gram, milligram and microgram illustrates just how small a microgram is (although it’s not possible to draw them to actual scale). Some trace minerals, like iodine and selenium are required only in microgram amounts.
What are vitamins?
Vitamins are a collection of complex carbon-based molecular compounds. Originally, it was thought that they belonged to a class of compounds known as amines and the term ‘vital amine’ – abbreviated to ‘vitamine’ – was coined to categorise them. It soon turned out that they were not amines – the term was kept but the final ‘e’ was dropped.
Vitamins are classified on the basis of their solubility, which has significant implications for nutrition and health:
Fat-soluble vitamins (A, D, E and K) can be readily stored in the body so that they are available when needed. This means they do not need to be taken daily, and if taken in excess, they can build up to toxic levels. For example, the recommended daily dose of vitamin D is 5μg, but at 5 times this dose, it is toxic and prolonged exposure can result in cardiac and kidney damage.
Water-soluble vitamins (B group and C) are not generally stored, and any excess intake is excreted in urine. They must be consumed frequently and in small doses. Too high a dose can result in toxic effects.
Although required in small amounts, vitamins have a wide range of physiological functions. For example, vitamin A is involved in the functioning of the eye, vitamin K is involved the production of blood clotting factors, and vitamin B1 (thiamine) plays a key role in carbohydrate metabolism
For most people, a balanced diet should provide all the necessary vitamins in appropriate amounts making supplements unnecessary.
Daily requirement of vitamin C
Dr Sean Bulley from Plant & Food Research along with Carolyn Cairncross from the New Zealand Nutrition Foundation explain the importance of vitamin C in the diet. Examples of plant foods rich in vitamin C are given, and advice is offered about the efficacy of vitamin C supplementation.
Point of interest
Some nutritionists believe that the daily dose of vitamin C is best taken in by consuming a plant food, like kiwifruit, rather than in tablet form. What is the reason for this?
What are minerals?
In addition to macronutrients and vitamins, the foods that we eat also contain small amounts of inorganic compounds as well as metal and non-metal ions. For example, the condiment ‘iodised salt’ contains mostly sodium chloride with a very small amount of potassium iodide. These compounds dissolve in the gut, releasing positively charged sodium and potassium ions and negatively charged chloride and iodide ions. Potassium, sodium and chloride ions play a crucial role in the water balance of the body and cell function. Iodide ions are needed in the production of the hormone thyroxine, which is responsible for metabolic regulation.
NaCl/KI(s) + water → Na(aq) + Cl(aq) + K(aq) + I(aq) iodised salt essential metal and non-metal ions
Some minerals are required in amounts greater than 100mg, and these are referred to as the macrominerals. There are 7 of them: calcium, phosphorus, chlorine, potassium, sulfur, sodium and magnesium. The recommended daily dose of these macrominerals ranges from 1–2g.
Dietary minerals
A section of the periodic table of the elements showing necessary dietary minerals. Some like sodium and calcium are required in quite large amounts. Others like iodine and selenium are only required in trace amounts.
The microminerals iron, copper, zinc and fluorine are needed in milligram amounts. For example, the recommended daily dose of iron for teenagers is 11mg for males and 18mg for females.
The trace minerals include iodine, selenium, vanadium, chromium, manganese, cobalt, nickel, molybdenum and tin and are needed in microgram amounts. For example, the recommended daily dose of iodine is 150μg, which is the amount in just under half a teaspoon of iodised salt.
Nature of Science
In his book The Trouble with Science, Professor Robin Dunbar, a University of Oxford anthropologist, states: “Science is a process of intense criticism.” It is this mechanism that keeps wild claims about health-promoting vitamin and mineral supplements under control. Unless the claims can be backed up with scientifically sound and peer-reviewed documented evidence, they remain questionable.
Useful links
The New Zealand Nutrition Foundation website has more information on vitamins.
The New Zealand Nutrition Foundation website has information on minerals.
