<prompt> In which of the following conditions smoking is protective?Ulcerative colitisCrohns diseaseSLEAlzheimers  <response>: Ans. a Ulcerative colitisRef : Harrison 19th ed. 1952-53EPIDEMIOLOGY OF IBP Ulcerative colitisCrohns diseaseMalefemale ratio 1:1 1.1-1.8.1Smoking May prevent disease May cause diseaseOral contraceptives No increased risk Odds ratio 1.4Appendectomy Protective Not protectiveMonozygotic twins 6 concordance 58 concordanceDizygotic twins 0 concordance 4 concordance 