Global smoking trends in inflammatory bowel disease: A systematic review of inception cohorts

Background and aims The effect of smoking on the risk of developing inflammatory bowel diseases (IBD) may be heterogeneous across ethnicity and geography. Although trends in smoking for the general population are well described, it is unknown whether these can be extrapolated to the IBD cohort. Smoking prevalence trends specific to the global IBD cohort over time have not been previously reported. This is a systematic review of smoking prevalence specific to the IBD cohort across geography. Methods A systematic literature search was conducted on Medline and Embase from January 1st 1946 to April 5th 2018 to identify population-based studies assessing the prevalence of smoking at diagnosis in inception cohorts of Crohn's disease(CD) or ulcerative colitis(UC). Studies that did not report smoking data from time of diagnosis or the year of IBD diagnosis were excluded. Prevalence of smoking in IBD was stratified by geography and across time. Results We identified 56 studies that were eligible for inclusion. Smoking prevalence data at diagnosis of CD and UC was collected from twenty and twenty-five countries respectively. Neversmokers in the newly diagnosed CD population in the West has increased over the last two decades, especially in the United Kingdom and Sweden; +26.6% and +11.2% respectively. Never-smokers at CD diagnosis in newly industrialised nations have decreased over the 1990s and 2000s; China (-19.36%). Never-smokers at UC diagnosis also decreased in China; -15.4%. The former-smoker population at UC diagnosis in China is expanding; 11% (1990-2006) to 34%(2011-2013). Conclusion There has been a reduction in the prevalence of smoking in the IBD cohort in the West. This is not consistent globally. Although, smoking prevalence has decreased in the general population of newly industrialised nations, this remains an important risk factor with longer term outcomes awaiting translation in both UC and CD.