Young children who develop respiratory tract infections may have an increased risk of developing asthma later in life, a new study has shown.

They may also have poorer overall lung function later on.

Dutch researchers looked at almost 155,000 children from several different European countries, including Ireland, who were born between 1989 and 2013.

Their history of respiratory tract infections was analysed between the ages of six months and five years. The children were then followed up until they were between the ages of four years and 15 years.

The study found that children who had suffered with upper respiratory infections, such as colds, laryngitis, sinusitis and tonsillitis, by the age of five years, had a 1.5-fold increased risk of developing asthma later in life.

Furthermore, children who had suffered from lower respiratory tract infections, such as general chest infections, bronchitis and pneumonia, had a two-to-four-fold increased risk of developing asthma later on. They were also more likely to have poorer lung function.

"These findings support the hypothesis that early-life respiratory tract infections may influence the development of respiratory illnesses in the longer term. In particular, lower respiratory tract infections in early life seem to have the greatest adverse effect on lung function and the risk of asthma," commented Dr Evelien van Meel of the Erasmus MC University Medical Centre in the Netherlands.

She noted that it is unclear at this stage whether the link between the two is causal.

"Further studies that measure lung function and wheezing from birth onwards are needed to explore whether the infections cause asthma and lower lung function, or whether wheezing and lower lung function may be predisposing these children to develop the infections.

"Studies that aim to prevent or treat respiratory tract infections at an early stage, perhaps by vaccination, would also help to shed light on this," she said.

The study took into account factors that could have affected the results, such as birth weight, lifestyle and socio-economic status.

The researchers plan to carry out further studies in this area.

"Specifically, we want to study the roles played by antibiotics, paracetamol and exposure to second-hand smoke in the relationships between respiratory tract infections and lung function or asthma.

"Also, we would like to study what percentage of the association between respiratory tract infections and asthma can be explained by changes in lung function, and whether the associations change when we take early-life wheezing into account," Dr van Meel said.

Details of these findings were presented at the European Respiratory Society International Congress in Milan, Italy.