Vitamins and minerals: How much do we need

It is quite easy to visualise the ‘building blocks’ of our food. Fat we can see as a lump of butter; protein as a piece of meat; carbohydrate as a slice of bread. Vitamins and minerals aren’t so obvious because they're invisible to the naked eye.

So how much do we need? And how much is enough?

Earlier this year, the Ministry of Health along with the National Health and Medical Research Council of Australia published a set of tables detailing the amount of 28 vitamins and minerals we need to eat each day, based on the best available scientific evidence.

You will see these amounts on food labels as the term %RDI, showing how much of the recommended amount a serving of that particular food provides. RDI stands for ‘recommended dietary intake’. These amounts are set according to age and many of them differ between men and women. They are deemed to be enough for almost all of us; that is 97-98% of healthy New Zealanders.

Nutrient reference values for Australia and New Zealand were published on 3 May 2006 and the full documents are available on the Ministry of Health website.

As well as preventing vitamin and mineral deficiencies, the latest recommendations also aim to combat the major killers in our society today – such as heart disease and cancers. For the first time, ‘suggested dietary targets’ (SDTs) have been included for the antioxidant vitamins, A, C, E and folate. These higher recommendations are based on amounts shown in research to help prevent these chronic diseases.

Amazingly, we still see New Zealanders going short of some vitamins and minerals. The most common is iron, a mineral not easily absorbed by the body. Others include folate, calcium, iodine, vitamin D and selenium.

The selenium content of New Zealand soil is particularly low, which is reflected in the lower amounts available in our food. Those in the North Island obtain more selenium from bread made from imported Australian wheat, but ‘Mainlanders’ still rely on other dietary sources, such as seafood, meat and eggs.

Our soil is also low in iodine, so we rely on this important mineral being added to our table salt. This has been done since the 1920s, helping to overcome our previously high rate of goitre. The consumption of iodised salt has decreased in more recent times, as has the use of iodine in the production of dairy products, and the government is, once again, faced with considering mandatory fortification of another food.

Some New Zealanders are also beginning to go short on vitamin D. This may be due, in part, to the increasing awareness of reducing time spent in the sun, so dietary sources are becoming increasingly important.