07:27am Monday 24 February 2020

Vitamins: myths, facts; use and misuse

Associate Professor Louis Roller

Associate Professor Louis Roller

“We are so constituted that we believe the most incredible things:
and once they are engraved upon the memory, woe betide him
who would endeavour to erase them”
— Goethe, 1774

Vitamins have caught the popular imagination. A recent study established that some 52 per cent of the Australian population takes some form of complementary medicine. It found that 37 per cent of these people were taking vitamins. Overall, 19.2 percent of the total Australian population – 4 million people – are taking vitamins. Many people take over-the-counter vitamins without professional advice and a few practitioners prescribe megavitamin therapy.

Vitamins have been commoditised and attracted big business.

But what are vitamins and how useful can they be when taken as supplements to a normal diet?

Vitamins are organic substances – or groups of related substances – that are found in many foods, have specific biochemical functions in the human body and are generally not made in the body (or not in sufficient quantity). They are essential nutrients required in very small amounts to maintain good health. The effects of vitamins are best known by their deficiency syndromes, many of them life-threatening.

The amount required for good health, all else being equal, is minute and can be readily obtained through a reasonable diet and sufficient exposure to sunlight. However, vitamin deficiencies still occur, even in affluent countries such as Australia, particularly in the case of folate, thiamine and vitamin D.

Vitamins in all shapes, forms, combinations and doses are sold through supermarkets, health-food shops and of course, pharmacies. The consumer, should be aware of the uses, efficacies and potential toxicities of any vitamin products they purchase.

So what does contemporary science tell us about vitamins?

There is a widespread perception in the world that if a tiny amount of something is good, then big is better and huge is best. There is also a line of reasoning that runs like this: “These are natural substances, so they must be safe in any quantity – right?” Wrong! The science tells us that in the case of vitamins, this rarely holds true.

Take vitamin A, for example. A number of recent reviews found no evidence of the benefits of vitamin A in preventing or treating a large number of diseases, including  the incidence of age-related maculopathy. It also found that vitamin A could in fact be harmful.

The antioxidant vitamins – vitamins A, E and C – are sold and used in large doses to those hoping they might prevent cancer, heart disease and dementias. Up until recent times, it had been thought that as these diseases have an oxidation component, the use of ‘natural’ antioxidant agents would have a beneficial effect – and that at the very least they could not do any harm. However, as logical as this sounds, it is far from the truth. Many clinical trials (double-blind and placebo-controlled), incorporating hundreds of thousands of individuals, over a period of many years have shown no statistically significant differences in morbidity and mortality.  However, there does seem to be small increase in mortality in the vitamins group. Further, a large study report published in October 2011 showed that there was a 1.6 times increase in prostate cancers in men who were using large doses of (“non-toxic”) vitamin E compared to a placebo group.

As for mega-doses 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 The trials in which vitamin C was introduced at the onset of colds as therapy did not show any benefit in doses up to 4 grams daily.

Takers of multivitamins might be similarly disappointed. At this point in time, there is no evidence indicating any benefits whatsoever in taking multivitamins. There is even some evidence indicating an increase in breast cancer.  During a mean follow-up of 9.5 years, in a Swedish study 974 women were diagnosed with incident breast cancer. Multivitamin use was associated with a statistically significant increased risk of breast cancer.

This is not to say that all vitamins taken as supplements are ineffective or dangerous. There are some vitamins that are used in larger-than-nutritional doses for therapeutic purposes.

Of all the vitamins, vitamin D has been most extensively studied and has been found to have many beneficial effects in supranutritional doses, including preventing and treating osteoporosis in susceptible individuals. The natural substance, cholecalciferol (D3) is the main active component of the various forms of vitamin D. The natural and most usual source is sunlight – it converts 7-dehydrocholesterol on the skin to cholecalciferol.

Just some of the other vitamins with a proven therapeutic use include folate (B9) in pregnant women to prevent ultimate spina bifida in the newborn, vitamin K for all newborns to prevent haemorrhagic disease, thiamine (B1) in individuals being treated for alcoholism and malnutrition, vitamin B12 in older persons suffering from pernicious anaemia and niacin (vitamin 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).

However one could say that these are exceptions that prove the rule that use of extra vitamins confers no health benefits.

People want good health and, because of the hyperbole surrounding the benefits of vitamins, there is a belief that supranutritional doses will improve their quality of life. In many cases, however, the perceived improvement does not match what today’s science tells us. The best way to be sure? Ask a pharmacist, knowing they will provide honest and up-to-date information.

Associate Professor Louis Roller works in the Department of Pharmacy Practice at Monash University.

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