DNA methylation was classified as ‘low,’ ‘intermediate,’ and ‘high,’ and asthma as ‘mild’ or ‘severe.’ In a dose-dependent manner, increasing methylation of ADRB2 was associated with more severe asthma, with those with intermediate methylation having an OR 4.11 (95% CI 1.58–10.73) for severe asthma and those with high methylation having an OR 7.63 (95% CI 3.02–19.26). This evidence concerns the gene ADRB2 and asthma.