The University of Bristol conducted research on almost 5000 children at age 7.5 years old. Using Mendelian randomization to look at changes in gene patterns they found a strong connection between asthma, BMI and body fat. Most significantly they found that the relative risk of asthma increased by 55 per cent for every extra unit of BMI.
The researchers concluded that a higher-than-average BMI increases the risk of childhood asthma and that public-health strategies designed to reduce obesity may help to decrease the global rise in asthma.
Reference: 'Effects of BMI, fat mass, and lean mass on asthma in childhood: a Mendelian randomization study' [open access] by Granell R, Henderson AJ, Evans DM, Smith GD, Ness AR, et al. (2014) in PLoS Med 11(7): e1001669. doi:10.1371/journal.pmed.1001669