Too much of a good thing?

By Amanda Johnson 18/10/2011

The debate about vitamin and mineral supplements was sparked again last week following the publication of two studies suggesting that vitamin and mineral supplements may be associated with increased mortality risk.

The Iowa Women’s Health study, just published in the Archives of Internal Medicine, assessed the use of vitamin and mineral supplements in relation to total mortality in 38 772 older women. Results showed that several commonly used dietary vitamin and mineral supplements may be associated with increased total mortality risk. The association was strongest with supplemental iron.

This study was picked up quite widely in the media. For example, an article in the New Zealand Herald last week reported

’The researchers confirmed their theory – that supplements were not helping people ward off death. But the reasons for the link to higher risk of overall mortality, or the risk of dying for any reason, were less clear…commonly used dietary vitamin and mineral supplements, including multivitamins, vitamins B6, and folic acid, as well as minerals iron, magnesium, zinc, and copper, were associated with a higher risk of total mortality.”

A second study, just published in Journal of the American Medical Association last week, looked at vitamin E supplementation and the risk of prostate cancer. This intervention study found that dietary supplementation with vitamin E significantly increased risk of prostate cancer among healthy men.

This type of research is nothing new. In 1994, a study published in the New England Journal of Medicine found that among male smokers aged 50 to 69 in south-western Finland there was a higher incidence of lung cancer among the men who received beta carotene supplements than among those who did not.

And last year the Science Media Centre collected expert comment for a Science Alert on supplements following the publication of a study that showed multi-vitamin supplements may increase risk of breast cancer. The experts quoted in this Alert recommended obtaining nutrients from a balanced diet and only taking supplements where there was a diagnosed nutrient deficiency.

Another interesting story in the media last week was the one about Time Magazine journalist John Gould, who took 22 pills a day, as well as protein bars and psyllium fibre, for five months. His doctor checked him out before and after his experiment and the only noticeable effect was that his vitamin D levels had increased, and so had his girth – by almost five kilograms.

It is becoming increasingly clear that we need to be cautious in our use of vitamin and mineral supplements. These latest studies confirm the advice I put together for the Dietitians New Zealand website last year, which states that:

’For most of us in New Zealand, a balanced diet will provide us with all the nutrients that we need for optimal health. Vitamin and mineral supplements are recommended for certain people, for example where there is a diagnosed nutritional deficiency, or increased nutritional requirement. High-doses of vitamin and mineral supplements may be dangerous and should be avoided. If several supplements are taken, it is important to check whether the cumulative effect is a high dose of any component.’

I think this still holds true, although for those people who wish to take a supplement as an ‘insurance policy’, I don’t think there is anything to worry about as long as it is a general multi vitamin/mineral supplement that provides a range of nutrients at levels that are around the ‘recommended daily intake’. And supplements certainly should not be considered as a substitute for a well-balanced diet.

0 Responses to “Too much of a good thing?”

  • It seems quite absurd to me that in first world countries people guzzle down expensive vitamins and supplements when a healthy diet is all that is required, while there are millions of people in the world suffering from malnutrition.

    A biochemist colleague of mine also points out that while many supplements are marketed as anti-oxidants, and therefore a good thing, there are mechanisms within our bodies which rely on oxidants to be effective.

    It is interesting that as people become more interested in sustainability some have suggested that vegetarianism is a way to reduce our impact on the planet but no-one has pointed out all the time and energy which goes into preparing supplements most of which are then flushed down the toilet (literally) and which then become an environmental contaminant.

  • Great to see your article. I had meant to ask if you could offer thoughts on this issue raised in a comment to my recent article that mentions work aimed at increasing calcium content of carrots, but it seems you have raised the key points without my asking!

    (I’ve linked to your article from there so that readers might find it.)

  • There’s also been recent evidence that taking vitamins may lead to an increase in risky behaviours (cover by Ben Goldacre here)

    It seems humans have a general set level of risk we are comfortable with, if we perceive that the risk has been reduced in some way we will alter our behaviour to keep a balance. Eg make cars safer -> people drive faster.

    Problem is when we do a false estimate of how much our risk is in the first place we may over correct our behaviours in response. Therefore an only modest benefit of vitamin supplements may be more than offset by destructive behaviours leading to a net decrease in health.