Health Check: can vitamins supplement a poor diet?

Vitamins and minerals are essential for keeping us in good health. While eating a varied diet should give us all the nutrients we need, recent diet and health surveys show the typical Australian diet is far from varied – or even close to what is considered a healthy diet.

To the rescue come vitamin and mineral supplements, but can they deliver on their promises and are they for everyone?

Who needs a supplement?

When writing about supplements, a glib approach is to state we can get everything we need from food, so we don’t need them. Eat your veggies. Don’t take supplements. End of story.

That isn’t the whole story, though. Already, our food supply is fortified with folic acid, iodine and thiamin to prevent serious public health issues related to conditions arising from deficiencies of these nutrients in some groups of people. So the rationale of needing to supplement for best health has some validity, but is underpinned by our generally poor eating habits to begin with.

There are groups of people for whom vitamin and mineral supplements would be recommended. Women planning pregnancy can benefit from a range of nutrients, such as folic acid and iodine, that reduce the risk of birth defects. People with limited exposure to sunlight would certainly be advised to consider a vitamin D supplement.

Frail and aged people are candidates as well due to food access problems, chewing and swallowing difficulties, absorption problems and medication. People with malabsorption problems, some vegetarians and people following chronic low-calorie diets all make the list as well. And, of course, people with a clinically diagnosed deficiency could all benefit from supplementation.

Why nutrients from food are better than from supplements

So should everyone take supplements “just in case”? Not so fast. Taking multivitamins as a nutritional insurance policy may be an issue for more than just your wallet. Seeing a supplement as a solution may contribute to neglecting healthy food choices, and this has bigger consequences for long-term health.

Food is a complex mix of vitamins, minerals and phytochemicals (plant chemicals). Phytochemicals are an important component of food and help to reduce the risk of conditions such as heart disease, type 2 diabetes and some cancers. Vitamin and mineral supplements do not provide the benefits of phytochemicals and other components found in food, such as fibre.

Whole foods usually contain vitamins and minerals in different forms – for example, vitamin E occurs in nature in eight different forms – but supplements contain just one of these forms.

If you look at habits linked to long-term health, it is eating plenty of plant-based foods that comes out on top, not so much taking supplements. This meta-analysis of 21 multivitamin-multimineral supplement clinical trials failed to find any benefit of improved life-expectancy or lower risks of heart disease or cancer from taking supplements.

The promise of possible benefits from supplements takes the focus from what really does promote better health and less chronic disease: eating a varied diet with plenty of minimally processed plant-based foods, regular activity, drinking within guideline recommendations and not smoking.

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

Formulations of multivitamins vary between manufacturers, with further market segmentation due to products aimed at different genders and life stages. For example, a multivitamin targeting women of childbearing age will likely be higher in iron than one for adult men. The government’s recommended dietary intakes for each vitamin and mineral are set out by gender and age, and manufacturers generally mirror these recommendations in their formulations.

Although taking too much of certain vitamins or minerals can be harmful, the doses present in multivitamins are typically low. After all, you can only pack so much of each nutrient into a multivitamin pill, and often it is not even close to the recommended dietary intake.

Vitamin and mineral supplements can’t replace a healthy diet, but a general multivitamin may help if your diet is inadequate or where there is already a well-supported rationale for you to take one. If you feel you could be lacking in certain vitamins and minerals, it is better to look at changing your diet and lifestyle first, rather than reaching for supplements.