The use of antibiotics in the first year of life is associated with an increased risk of asthma at the age of seven years, a new study has found, and the reason may be that antibiotics destroy not only disease-causing microbes, but also those that are helpful to the developing immune system.Antibiotic use had a greater impact on children who would otherwise be considered at lower risk — children who lived in rural areas and those whose mothers did not have asthma — than on those who were already at increased risk because of an urban environment or genetic predisposition.Studies of antibiotic use and asthma have been complicated. Because antibiotics are used to treat respiratory illnesses, which are often precursors of asthma, it has been difficult to determine the effect of antibiotics alone. But this study found that the risk of asthma increased even in children treated with antibiotics for non-respiratory illnesses in the first year of life. Anita L Kozyrskyj, the lead author and an associate professor of pharmacy at the University of Manitoba, said the findings supported what scientists call the microflora hypothesis — that “you need good bacteria in your digestive tract for normal development of the immune system so that you don’t end up with asthma,” as she put it.The researchers tracked medications by examining prescription records, and determined asthma status by treatment for asthma or any asthma drug use in the year following the seventh birthday. Six per cent of the children developed asthma by the age of seven years.After statistically adjusting for respiratory and non-respiratory illnesses, sex, maternal history of asthma, urban or rural location and other factors, researchers found that one or two courses of antibiotics in the first year of life increased the risk of asthma by about 20 per cent. The more frequent the antibiotic use, the higher the risk. Three to four courses of medicine conferred a 30 per cent added risk, and more than four courses of antibiotics increased the risk by almost 50 per cent.
