In all analyses, SOD3 R213G is used as a continuous variable for maximal power. Cox regression was with entry at 1977, when the Danish Patient Registry began, thus including both incident and prevalent cases. Any asthma: either self-reported asthma, a hospital diagnosis of asthma, or medication for asthma among never-smokers. Allergic asthma: individuals with any asthma who also reported allergy triggers such as food, grass, flowers, animals, or others. *Combined in a fixed effect meta-analysis using the metan command in STATA. OR, odds ratio from logistic regression; CI, confidence interval. In the CGPS, a total of 99,958 R213G non-carriers (97.5%), 2,533 R213G heterozygotes (2.5%), and 15 R213G homozygotes (0.01%) were identified. In the CCHS, 8,634 were R213G non-carriers (97.6%), 207 were R213G heterozygotes (2.3%), and 2 (0.02%) were R213G homozygotes.