When it comes to using vitamins to supplement diets, there’s a wide gap between what science says and what many consumers believe.
A recent study, for instance, established that some 52% of the Australian population takes some form of complementary medicine, with over a third of this number taking vitamin pills.
Overall, almost one in five people in Australia are taking vitamins. Many of these people take over-the-counter supplements without professional advice, although a few practitioners prescribe megavitamin (large doses) therapy.
But most are vitamins not really useful when taken as supplements to a normal diet. In fact, such supplements are potentially harmful.
Still, vitamins in all shapes, forms, combinations and doses are sold through supermarkets, health-food shops and pharmacies. So consumers should be aware of the uses, efficacies and potential toxicities of any vitamin products they purchase.
What are vitamins?
Vitamins are organic substances – or groups of related substances – found in many foods. They have specific biochemical functions and are generally not made in the body (or not in sufficient quantity for good health).
They’re essential nutrients required in very small amounts to maintain good health. The effects of vitamins are best known by their deficiency syndromes, many of which are life threatening.
All else being equal, the amount of these nutrients required for good health can be readily obtained through a reasonable diet and sufficient exposure to sunlight.
But people still suffer from vitamin deficiencies, even in affluent countries, such as Australia, particularly in the case of folate, thiamine and vitamin D.
Science and vitamins
There’s a widespread perception that if a tiny amount of something is good, then more is better and a lot is best.
There’s also a line of reasoning that runs like this: these are natural substances, so they must be safe in any quantity. Wrong. Science tells us that in the case of vitamins, this rarely holds true.
Take vitamin A as an example. A number of recent reviews have 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, in which the retina degenerates.
Vitamin A could, in fact, be harmful. But antioxidant vitamins – A, E and C – are sometimes used in large doses by people hoping to prevent cancer, heart disease and dementia.
That’s because until recently, it was thought that as these diseases have an oxidation component and the use of “natural” antioxidant agents would have a beneficial effect.
Or the same old chestnut: at the very least they could do no harm. Now it’s been established that this 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 between the antioxidant group and the control group.
In fact, there seems to be a small increase in mortality in the group taking vitamins.
A large study published in October showed a 1.6 increase in prostate cancers in men who were using large doses of (“non-toxic”) vitamin E compared to the placebo group.
More bad news
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’s no evidence indicating any benefits whatsoever in taking multivitamins. There’s even some evidence indicating an increase in the incidence of breast cancer: in a Swedish study, multivitamin use was associated with a statistically significant increased risk of breast cancer.
Good use
This is not to say 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 most usual source of which is sunlight.
Some 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 and;
vitamin B12 in older people suffering from pernicious anaemia; and
niacin (vitamin B3) in large doses for the treatment of high cholesterol where other therapies have failed (although niacin is poorly tolerated by many individuals, and can cause serious side effects).
But 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’s a belief that supranutritional doses will improve their quality of life. But in most cases, the perceived improvement doesn’t match what science tells us.