There was seemingly bad news for supplement-takers recently when The Lancet published a study which found that 'antioxidant' nutrients (such as beta-carotene, vitamins A, C and E and selenium) appeared not to reduce the risk of cancer in the digestive tract. The study authors also claimed that taking antioxidants might speed our demise. Emblazoned across the cover was the quote: 'The prospect that vitamin pills may not only do no good but can also kill their consumers is a scary speculation, given the vast quantities that are used in certain communities.' Not surprisingly, I've had a fair few requests to respond to what looks to be a bitter pill to swallow.

The Lancet study used a meta-analysis, where the results of several studies are pooled to get a more accurate assessment of a treatment than can be achieved by examining individual studies alone. The meta-analysis looked at 14 trials, of which only seven were appropriate for appraising the effect of supplements on risk of death. Close inspection of these seven studies reveals that six showed no significant increase in mortality. The overall results seem to have been somewhat skewed by one study, the results of which were out of keeping with the others.

This last point was highlighted in an editorial accompanying the study. The statistician authors of this editorial also pointed out that the statistical analysis used was not the most appropriate for this study. When a more relevant test (a 'random-effects meta-analysis') was applied, the apparent increase in mortality disappeared.

The study that did show increased mortality was one in which supplementation with synthetic beta-carotene was found to increase death due to lung cancer in smokers and asbestos workers. This is not the only study that has found such a link, so my advice is for smokers to avoid supplementation with beta-carotene.

The apparent lack of benefit from taking antioxidants was another surprise that came out of the study. However, the meta-analysis included studies that varied in nutrients and dosages. With such variability, it is hard to get an overall picture. Also, the duration of the studies may not have been long enough to see benefits. It is also possible that because the Lancet study only looked at digestive-tract cancers, it may have missed other benefits with regard to cancer or conditions such as stroke.

The deficiencies in this study's scope and methodology led the authors of the editorial to conclude that it did 'not offer convincing proof of hazard'. Oddly, the Lancet's front-cover splash was lifted (out of context) from the same editorial. It's a sad day for science when one of the world's most respected medical journals chooses not to let the facts get in the way of a good story.

Dear John

I have worn contact lenses for 10 years. For the last two years I have had a type of conjunctivitis which has precluded me from wearing them. I am now back to wearing lenses, but suffer from dry eyes. Someone told me that omega-3 supplements may help alleviate my dry eyes. Is this true?
Stephen

The surface of the eye is kept moist by tears secreted by the lachrymal glands. Also, moisture is held in the surface of the eye. There is evidence that dryness of the eyes may be caused by a deficiency of healthy fats, or essential fatty acids. While it is possible that omega-3 fats (such as fish oils) may help dry eyes, there does not seem to be any research on this. The science in this area has focused on fats known as gamma linolenic acid (GLA) and linoleic acid (LA) - both of which are of the omega-6 class. In one study, supplementation with GLA and LA helped to reduce the symptoms of dry eyes. This study found that omega-6 supplements reduced inflammation, too - and this might help to control your conjunctivitis symptoms. Take 1g of evening primrose oil (which is rich in both GLA and LA) twice a day.

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 drbriffa.com. Before following any recommendations in this column, you should consult your own medical adviser about any medical problems or special health conditions

Nutrition news

One critical process in health is the balancing of blood-sugar levels in the bloodstream. Low blood-sugar levels cause an under-fuelling of body and brain that can lead to problems with fatigue, food cravings and mood. However, in a recent study published in this month's edition of the journal Diabetes Care, evidence has turned up that high blood-sugar levels may also adversely affect our physical and emotional well-being.

In this study, infusing diabetic individuals with sugar to raise their blood-sugar levels was found to reduce mental functions such as information processing, memory and some areas of attention. High levels of blood sugar were also associated with feelings of agitation, anxiety, lethargy and a reduced sense of happiness.

This study suggests that for optimal wellbeing, it is best to avoid eating too much in the way of foods that release sugar rapidly into the bloodstream. Foods to moderate include sugary drinks, biscuits, confectionery, potatoes, breakfast cereals and wheat-based breads.