Friday, July 09, 2004

Vitamins and asthma

'Children who take multivitamins may be at a greater risk of developing asthma and food allergies,' says a report from BBC News. According to research from the Children's National Medical Center in Washington, there appears to be an association between early infant multivitamin intake and asthma among black infants, and an association between early infant multivitamin intake and food allergies in formula-fed infants. The study contradicts earlier research which suggested that lower levels of vitamins were associated with higher rates of asthma.

Whatever the relationship between vitamins and asthma, this study sheds not one ray of light upon it.

This study is based on a multivariate analysis - that is, a group of patients with a variety of different characteristics were studied. For those patients with asthma and food allergies, these characteristics were cross-referenced with each other to see which ones were significant. The combinations that were significant seem very odd and inconsistent. For example, early use of vitamins increases the risk of asthma among black infants, but not white infants. Food allergies were increased by vitamin use in formula-fed children, but not breastfed children, if done at an early age. However, food allergies occurred in both formula-fed children and breastfed children if they were given vitamin supplements at the age of three. The relative risks involved seem quite small, too.

The most likely explanation is that these results were statistical quirks plucked from scores of other combinations of factors that showed no relationship at all. The lack of any plausible mechanism to explain the results also suggests that there is nothing to them.

But even if the figures are not merely statistical artefacts, there are other reasons to believe that this research may not be all it is cracked up to be. Asthma UK adviser Dr Seif Shaheen has pointed out that the relationship may be the other way around: children with asthma-like symptoms may be given multivitamins in an attempt to improve their health. Moreover, he added, 'it is hard to diagnose asthma in in children under the age of five. Hence, some children with "asthma" at three years may have suffered with transient wheeze rather than allergic asthma, which may have disappeared as they grew older'.

Others were surprised by the results, too. The BBC quotes Frankie Phillips of the British Nutrition Foundation, who called the results 'surprising'. The only thing that wasn't surprising was the suggestion from the study team that 'more research was needed'. Well, they would say that, wouldn't they?

BBC NEWS | Health | Early vitamin use link to asthma

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