Ashma sufferers kidsThe increase in asthma risk in children could be explained by the rise in body mass index (BMI), according to new research.

A study used genetic data to show that higher BMI increases the risk of childhood asthma using Mendelian randomization to look at changes in gene patterns in almost 5,000 children when they were aged seven and a half.

Using a weighted genetic score they found a strong connection between asthma, BMI and body fat. Most significantly they found that the relative risk of asthma increased by 55% for every extra unit of BMI.

The findings published in www.plosmedicine.org suggest that a higher-than-average BMI increases the risk of childhood asthma and that public-health strategies designed to reduce obesity could also help to stem the global rise in asthma.

Lead researcher Dr Raquel Granell, research fellow in the school of social and community medicine of the University of Bristol, said: "We have found, for the first time, strong evidence of a causal effect of increased BMI on increased risk of asthma in mid-childhood, however mechanisms operating through lean mass and other non-BMI related factors are also likely to play a role."

Incidence of asthma has been rising steadily over the past few decades. According to Asthma UK, 1.1 million children (1 in 11) and 4.3 million adults (1 in 12) are currently receiving treatment for asthma at a cost of £1 billion a year to the NHS.