Antibiotic use early in life does not increase the subsequent risk of asthma

Antibiotic use early in life does not increase the subsequent risk of asthma, according to a new study by an international team of researchers.  The study is published in the June 2004 edition of the International Journal of Epidemiology (IJE) edited in the Department of Social Medicine at the University of Bristol.

Previous research has indicated that infections in early life may offer protection from developing asthma.  Therefore, it has been suggested that antibiotics increase the risk of asthma by reducing the protective effect of infections or by interfering with normal bacterial flora in the gut.  However, research on this hypothesis has yielded conflicting results. 

Several, but not all, studies have observed an association between antibiotics and asthma.  However, the key issue is whether these associations are causal or whether they are due to ‘reverse causation’ – that is, children who are already predisposed to asthma get more respiratory infections and thus use more antibiotics.

The researchers, led by Dr Sunia Foliaki of the University of Wellington, New Zealand carried out an ecological study that compared antibiotics sales in 28 countries with the prevalence of symptoms of asthma, rhinitis and eczema in 13-14 year olds in those countries. 

By comparing populations as a whole instead of looking at individuals within those populations, the researchers hoped to avoid the possibility of ‘reverse causation’ confounding the results. 

As previous studies have found an association between the level of ‘Westernization’ or ‘affluence’ of a country and asthma prevalence, the researchers also adjusted their analyses to take into account the gross national product (GNP) of each country (GNP being a readily available marker for a country’s level of affluence).

 In the unadjusted analyses, the researchers found a positive correlation between per capita antibiotics sales and the prevalence of asthma, rhinitis and eczema.  However, the associations between antibiotic sales and asthma were negative once the analyses had been adjusted for GNP. 

Dr Foliaki said: “These findings are generally not consistent with the hypothesis that antibiotic use increases the risk of asthma, rhinitis or eczema.  Even if there is a possibility that, in some circumstances, antibiotic exposure early in life may increase the subsequent risk of developing asthma, this does not account for the international differences in asthma prevalence.  Other risk factors for asthma must account for the observed international patterns.”

In a commentary on the paper, Dr Juha Pekkanen of the National Public Health Institute in Kuopio, Finland said: “Given the problems of studying the association between use of antibiotics and risk of asthma at the individual level, this ecological study is interesting.  The results suggest that the amount of antibiotic use does not explain the geographical differences in the prevalence of asthma and therefore they are not likely to be the major cause of the increase in asthma in the developed world. “