Of 71 studies, only 14 (19.7%) conducted a multivariate analysis for at least one inflammatory biomarker, adjusting for potential confounders such as age, sex, body mass index, ethnicity, inhaled corticosteroids, season/month of blood collection, sun exposure, vitamin D supplementation, vitamin D binding protein level, socioeconomic status, smoking status, alcohol consumption, upper respiratory tract infections, pulmonary function, and/or asthma status [29–32, 34, 46, 57, 66, 73, 83, 86, 89, 95, 103]. This evidence concerns the gene GC and asthma.