Nutrition expert Professor Tim Crowe explores when vitamins and supplements can improve nutrition.

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There is a vast range of vitamins and minerals that our body needs to keep us in good health. And while a varied diet should give us all the nutrients we need, recent diet and health surveys show that the typical Australian diet is far from varied enough – or even close to what is considered a healthy diet.

One solution many of us turn to is vitamin and mineral supplements. But can they deliver on their promises, and are they for everyone?

There certainly are groups of people for whom vitamin and mineral supplements may be recommended. For example, women planning pregnancy, people with malabsorption problems, some vegetarians, people following chronic low-calorie diets and of course, people with a clinically diagnosed deficiency could all potentially benefit from supplementation.

Already, our food supply is fortified with folic acid, iodine and thiamine, which helps address public health issues related to deficiency of these nutrients. So the rationale of needing to supplement for better health is valid to a degree, though it is underpinned by our generally poor eating habits to begin with.

Can supplements make up for a nutritionally poor diet?

So should everyone be taking supplements? Not so fast. Food is made up of a complex mix of vitamins, minerals and phytochemicals (plant chemicals). Phytochemicals are an important component of food and help to reduce the risk of heart disease and some cancers.

Vitamin and mineral supplements do not provide the benefits of phytochemicals and other components found in food, such as fibre. That means taking vitamin and mineral supplements can never be a substitute for a healthy, varied diet.

"So should everyone be taking supplements? Not so fast. Vitamin and mineral supplements can never be a substitute for a healthy, varied diet."

Why taking mega-doses isn't a great idea

Many people believe that taking mega-doses of certain vitamins will act like medicine to cure or prevent certain ailments. However, large-scale studies have consistently shown there is little benefit in taking mega-doses of supplements. In fact, there is evidence that taking high-dose supplements to prevent or cure major chronic diseases, such as heart disease and cancer, may be harmful to your health.

For instance, vitamin A (beta-carotene) was once thought to reduce the risk of some cancers, but supplements have been linked to an increase in lung cancer rates in smokers. It’s also been suggested that high doses of vitamin A may cause issues with the, liver, bone and skin.

High levels of vitamin B6 have been linked to some forms of nerve damage. Doses of vitamin C above one gram can cause diarrhoea. Excessive doses of some minerals may also cause problems – iron toxicity being a known problem in causing gastrointestinal upset, nausea and black bowel actions.

For a healthy adult, if supplements are used, they should normally be taken at levels close to the recommended dietary intake (RDI) level. High-dose supplements should not be taken unless recommended under medical advice.

Vitamin and mineral supplements can’t replace a healthy diet, but a general multivitamin may help if your diet is inadequate. If you feel that you could be lacking in certain vitamins and minerals, it is better to look at changing your diet and lifestyle first though, rather than reaching for supplements.

For more information on recommended dietary intakes, check out the Nutrient Reference Values for Australia and New Zealand.

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