Thumb sucking or nail biting in childhood and adolescence is associated with an increased risk of Crohn’s disease: results from a large case–control study
Creators: name: Teich, Niels
name: Mohl, Wolfgang
name: Primas, Christian
name: Novacek, Gottfried
name: Gauss, Annika
name: Walldorf, Jens
name: Felten, Gisela
name: Atreya, Raja
name: Kruis, Wolfgang
name: Bettenworth, Dominik
name: Roznowski, Artur Bartosz
name: Langhorst, Jost
name: Schmidt, Karen
name: Bruns, Tony
name: Stallmach, Andreas
Publisher: name: Taylor & Francis
Year: 2020
Subjects: subject: Space Science
subject: Medicine
subject: 59999 Environmental Sciences not elsewhere classified
subject: FOS: Earth and related environmental sciences
subject: FOS: Earth and related environmental sciences
subject: 39999 Chemical Sciences not elsewhere classified
subject: FOS: Chemical sciences
subject: FOS: Chemical sciences
subject: Ecology
subject: FOS: Biological sciences
subject: FOS: Biological sciences
subject: Immunology
subject: FOS: Clinical medicine
subject: FOS: Clinical medicine
subject: 69999 Biological Sciences not elsewhere classified
subject: Cancer
subject: Science Policy
subject: 110309 Infectious Diseases
subject: FOS: Health sciences
subject: FOS: Health sciences

description: The hygiene hypothesis suggests that a reduction in microbial exposure contributes to an impaired immune response later in life and increases the incidence of immune-mediated diseases such as inflammatory bowel diseases (IBD). Thumb sucking and nail biting are two early habits that modulate the oral microbiota composition and antigen load. We hypothesized a lower risk of Crohn’s disease (CD) and ulcerative colitis (UC) in adults with prior thumb sucking and nail biting. 918 IBD cases and their 918 siblings without IBD were asked to fill out a survey containing 32 questions on environmental factors in childhood and early adulthood. Prevalence of thumb sucking and/or nail biting at the usually well-remembered time of (1) school enrollment and (2) coming-of-age ceremonies was the predefined combined risk factor of this study. 65% of the patients were female and 57% suffered from CD. About 49% of IBD patients but only 44% of their siblings reported thumb sucking/nail biting at the time of school enrollment or coming-of-age (<i>p</i> = .007). Sensitivity analysis revealed that this difference was observed in patients with CD (50% versus 41%; RR= 1.22; 95% CI 1.09–1.37, <i>p</i> = .001) but not in patients with UC (49% versus 48%; RR= 1.02; 95% CI 0.90–1.17; <i>p</i> = .83). Contrary to our expectation and challenging the hygiene hypothesis, we found that common oral habits are not protective against IBD. Instead, nail biting at the time of school enrollment and coming-of-age was a statistically significant risk factor for CD in our cohort. Key summary <b><i>Evidence available before this study:</i></b> The hygiene hypothesis suggests that a reduction in microbial exposure due to improved health activities has contributed to an immunological imbalance in the intestine and an increased incidence of allergic and autoimmune diseases. A population-based birth cohort study has demonstrated that thumb-sucking and nail biting in children lead to a reduction of the risk of atopic sensitization, asthma, and hay fever. <b><i>Added value of this study:</i></b> Contrary to the hypothesis, thumb sucking and nail biting were not associated with a reduced risk of IBD. Instead, thumb sucking and/or nail biting at the usually well-remembered points in time of school enrollment and of religious or secular coming-of-age ceremonies was associated with a higher risk of Crohn’s disease but not of ulcerative colitis. Our data did not support the hygiene hypothesis, one pathogenic concept in the context of IBD.