Australasian Science: Australia's authority on science since 1938

Vitamins: Perception versus Reality

By Louis Roller

Which vitamins are backed by scientific evidence and which don’t live up to the hype?

If you get your health advice from the internet, you could be forgiven for thinking that multivitamins, and lots of them, will cure a multitude of problems and contribute hugely to your health, happiness and “wellness”. That is far from the truth. You might even be doing yourself considerable harm.

Around 52% of the Australian population takes some form of complementary medicine, with 37% of them taking vitamins. Overall, 19.2% of the Australian population – some 4.4 million people – take vitamins. These are usually over-the-counter vitamins taken without professional advice, although some practitioners prescribe megavitamin therapy. It’s no wonder, then, that vitamins have been commoditised and attract big business.

Vitamins are organic substances found in many foods. They have specific biochemical functions in the human body but are generally not made in the body – or not in sufficient quantity. They are essential nutrients requiring very small amounts to maintain good health, with their effects best known by their deficiency syndromes, many of them life-threatening.

The minute amounts required for good health, all else being equal, are readily obtained through a reasonable diet and sufficient exposure to sunlight. However, even in affluent countries such as Australia, vitamin deficiencies still occur, particularly folate, thiamine (Vitamin B1) and vitamin D.

Vitamins in all forms, combinations and doses are sold through supermarkets, health-food shops and pharmacies. Consumers should be aware of the uses, efficacies and potential toxicities of any vitamin products they purchase, but there is a widespread perception that if a tiny amount of something is good then big is better and huge is best. People also reason that “these are natural substances, so they must be safe in any quantity – right?” Wrong! Science reveals that this rarely holds true for vitamins.

For example, a number of recent reviews found no evidence of the benefits of vitamin A in preventing or treating many diseases, including age-related maculopathy. It could, in fact, be harmful.

The antioxidant vitamins A, E and C are sold in large doses to those hoping to prevent cancer, heart disease and dementias. Until recently it was thought that since these diseases have an oxidation component, the use of “natural” antioxidant agents would be beneficial and at least could do no harm.

However, while this sounds logical it is far from the truth. Many double-blind placebo-controlled trials incorporating hundreds of thousands of individuals over many years have shown no statistically significant differences in morbidity and mortality. In fact, there even seems to be a small increase in mortality in the vitamin-taking group.

As for using megadoses of vitamin C to prevent and treat the common cold, the news is not good. A 2005 meta-analysis of a large number of trials found that vitamin C supplementation failed to reduce the incidence and intensity of colds and had no benefit in preventing the onset of colds in doses up to 4 g/day.

Those who take multivitamins might be similarly disappointed. To date there is no evidence indicating any benefits whatsoever in taking multivitamins. There is even some evidence indicating an increase in breast cancer. This is not to say that all vitamins taken as supplements are ineffective or dangerous, as some can be used in larger-than-nutritional doses for therapeutic purposes.

Of all the vitamins, vitamin D has been most extensively studied and shown to have many effects in supranutritional doses, predominantly in preventing and treating osteoporosis in susceptible individuals. Some other vitamins with a proven therapeutic use include folate (B9) in pregnant women to prevent spina bifida in the newborn; vitamin K for all newborns to prevent haemorrhagic disease; thiamine (B1) for treating alcoholism and malnutrition; vitamin B12 in older people suffering from pernicious anaemia; and niacin (B3) in large doses for the treatment of hypercholesterolaemia where other therapies have failed (although niacin is poorly tolerated by many individuals and can cause serious side-effects).

People want good health. Because of the hyperbole surrounding the benefits of vitamins, they believe that supranutritional doses will improve their quality of life, but the promised benefits do not match what today’s science tells us.

Louis Roller is Associate Professor Faculty of Pharmacy and Pharmaceutical Sciences at Monash University, and was on the Pharmacy Board of Victoria for 22 years.