Asthma is a chronic and complex condition that can be difficult to diagnose. The annual prevalence of asthma in the UK is estimated to be 6.0 million people. Although there is evidence to suggest that the prevalence of asthma has plateaued in the UK since the 1990s, the NHS still spends around £1.1 billion on treating individuals with asthma. Observational studies have provided evidence of a positive association between adiposity (measured as body mass index (BMI)) and risk of asthma in both children and adults. Since the prevalence of asthma remains high, identifying modifiable risk factors, such as body composition, should be a priority. Since observational studies can suffer from confounding, we would like to apply Mendelian randomization analyses to the ALSPAC dataset to determine whether body composition has a causal effect on the risk of asthma.