People with asthma have an increased risk of becoming obese, a new study suggests.

It is already known that obesity is a risk factor for developing asthma, however these latest findings indicate that the reverse is also true.

"We already know that obesity can be a trigger for asthma, perhaps via a physiological, metabolic or inflammatory change. Until now, there has been very little research on whether the reverse is true - whether asthma can lead to obesity. In this study, we have enough people and we have followed them for long enough to observe the relationship between these two conditions," explained Dr Subhabrata Moitra of the Barcelona Institute for Global Health in Spain.

The study involved over 8,600 people from 12 countries, none of whom were obese at the outset. The participants were followed up after 10 years, and again after 20 years. The researchers investigated the link between having asthma at the start of the study and the likelihood of being obese 10 years later.

They also studied people who had developed asthma 10 years into the study, looking at their risk of obesity by 20 years. Other risk factors were also taken into consideration, such as age and physical activity.

The study found that those with asthma at the start of the study had an increased risk of being obese 10 years on compared to those who did not have asthma.

Furthermore, the increase in the risk of obesity was even greater among people whose asthma began in adulthood. It was also greater among those with non-allergic asthma.

"By following a large number of study participants over two decades, we have been able to observe how having asthma increases a person's risk of going on to become obese, especially if their asthma begins in adulthood or if they have asthma but no allergies.

"Our findings suggest the relationship between the two conditions is more complicated than we previously realised. It's important that we do more work to pick this apart. For example, we do not know why having asthma increases the risk of developing obesity or whether different asthma treatments have any effect on this risk," Dr Moitra commented.

Details of these findings were presented at the European Respiratory Society International Congress in Paris.