The major criticisms of these studies are measurement bias (to be included patients needed to have had vitamin D measured); the retrospective assessment of remission; how disease severity was controlled for; and the lack of data relating to concomitant corticosteroid therapy or vitamin D supplementation.26 This is the first prospective study with a large enough sample size to adjust for potential confounders to examine the association between pretreatment vitamin D status/concentration and clinical outcomes in patients with Crohn’s disease treated with anti-TNF therapy. This evidence concerns the gene TNF and Crohn disease.