The bulk of the evidence shows that popping vitamin and mineral pills is safe and beneficial. However, stories do occasionally surface suggesting that nutritional supplements are at best useless, and at worst may actually increase our susceptibility to illness. My experience is that the studies behind such stories often do not stand up well to scientific scrutiny. Some suggest that the press ignores critical detail in its rush to make good copy and boost sales. My reckoning is that cries for more responsible journalism should be focused less on the lay press and more on the medical journals that publish scientifically suspect studies.
This was at the forefront of my mind as a result of being asked to give a talk on scare stories about supplements, and the forces behind them. Two days before my lecture, the British Medical Journal (BMJ) sported the headline: 'Vitamin and minerals for elderly people - No good evidence that they reduce infections'. It pooled the results of several studies which had assessed the effect of supplementation on infections in the elderly. Three effects were measured: the number of ill days caused by infection (outcome 1), the number of people who suffered at least one infection during the study (outcome 2), and the average number of infections suffered by participants (outcome 3). The study found that, compared to placebo (inactive medication), supplementation did not bring significant reductions in outcomes 2 or 3. The authors concluded that the evidence for the elderly taking nutrient supplements was 'weak'.
One might argue that it is more relevant to consider what effect nutritional supplementation has on outcome 1. This BMJ study showed that taking a daily multivitamin and mineral pill reduced the number of ill days by more than 17 per year - a result that was highly statistically significant. So the slant given to the results of this study by its authors and the BMJ seems curious.
What is even more puzzling is that very shortly after this study was published, the deputy editor of the BMJ posted an electronic response questioning the validity of two of the studies within it that found benefit. It does seem odd that this issue did not come to light prior to publication. And one wonders what all of this says about the much-lauded peer-review process, where academics are responsible for ensuring poorly conducted or suspect studies do not make it to publication. While medical journals are seen to uphold the values of intellectual and scientific rigour, it seems they are no different from newspapers regarding their capacity to churn out bad press.
Dear John
I'm 76 and have recently suffered from episodes of blurred vision and a sweet taste in my mouth. My doctor took a blood test which revealed I have 'pre-diabetes'. She told me to avoid simple sugars. As I do not eat these, I asked my doctor if my intake of starches such as bread and rice might be a problem. She said I can eat as much starch as I like. Yet my symptoms do come when I eat starchy foods. Would you care to comment?
Dorothy Holister, France
Pre-diabetes is a condition characterised by blood-sugar levels that are higher than normal. Your doctor is right to advise you to avoid foods with added sugar (ie biscuits, cakes, soft drinks, fruit yogurts), as these upset blood-sugar levels. However, grain-based foods can disrupt blood-sugar levels to an extent similar to sugar. Many forms of bread and rice cause considerable problems, particularly if eaten in quantity. Your doctor is simply wrong in suggesting that such foods can be eaten with impunity. Slower sugar-releasing forms of carbohydrate include vegetables (although not potatoes), beans and lentils.
Nutrition news
Last week my column focused on the association between meat consumption and colon cancer. Contrary to popular opinion, this association is far from established. However, there is some suggestion that processed meat including bacon, sausages and hot dogs may pose particular problems for the body because of the chemicals they contain.
Supportive evidence for this notion has very recently come from a study presented at a meeting of the American Association for Cancer Research. This study found that individuals consuming the most processed meat were at a 67 per cent increased risk of pancreatic cancer compared to those consuming the least. Detailed analysis of the data revealed that the saturated-fat content of the meat was unlikely to contribute to the cancer-causing mechanism. The researchers suggested that it is the generation of potentially carcinogenic chemicals (such as heterocyclic amines and polycyclic aromatic hydrocarbons) during the manufacturing of processed meat that may be to blame.
The results of this research support the concept that it is the chemicals within meat, not the meat itself, that are likely to be responsible for meat's mooted link with cancer.
· If you have any issues you would like Dr Briffa to address in his column, please email him on john.briffa@observer.co.uk. Please note that Dr Briffa cannot enter into any correspondence. You can also visit www.drbriffa.com. Before following any recommendations in this column, you should consult your own medical adviser about any medical problems or special health conditions
