67 In 2006 the proportion of Asian patients with a discharge diagnosis of UC was similar to that of the total population.67 Gender.  The majority of studies from the West have shown an equal gender Tamoxifen distribution for UC and CD, although some studies have reported a slight female predominance for CD and a male predominance in UC.2,12,68,69 In contrast, most studies in Asia including data from China,27,70–74 Hong Kong,24,25,75 Japan,15,16,28,52,76 Korea,13,77 Singapore,31,33 India78 and Sri Lanka79

have demonstrated a male predominance for CD, with the exceptions of one study from Sri Lanka showing an equal gender distribution for CD.35 For UC, a growing number of studies in Asia have shown an equal gender distribution.13,26,29,52,80 There are also several studies demonstrating male predominance,16,25,28,31,55,70,81–83 and three studies demonstrating a female predominance in UC.35,56,84 Age.  In the West, the median age of onset of CD is 20 to 30 years and for UC is 30 to 40 years.2,85 Consistent with findings in the West, CD in Asia is diagnosed at a younger age than UC.13,16,31,33,35,70,73,75,79,86 The median age of diagnosis of CD was 22.5 years in two studies from Korea.13,77 The median age of diagnosis of UC in Asia is similar, or slightly older than in the West, ranging from 35 to 44 years.13,16,25,26,31,35,55,70,73,79–81,84,86,87

With the exception of a Korean study,13 studies from Asia13,18,55,79 have not identified a second peak in IBD incidence as seen in the 6th and Wnt inhibitor 8th decades in Western countries.88 Patients with IBD in Hong Kong were diagnosed at an older age compared with Caucasians Leukotriene-A4 hydrolase in Melbourne, Australia (median age 30 vs 24 years for CD; 38 vs 30 years for UC).89 This may be partly explained by a delay in diagnosis in Hong Kong. Familiarity leads to shortened time from symptom onset to diagnosis; for example in Denmark the median symptom duration prior to diagnosis of CD was 2.2 years in 1962–1987 and 0.7 years in 2003–2004.90 Family history.  Studies in Asia have reported a family history

in 0.0–3.4% of IBD patients.24–26,29,31,33,71,75,77,81,86 This figure is lower than the 10–25% in Western countries.91–93 A recent study from Sri Lanka showed that a family history of IBD was present in 2.1% of UC patients, and 5.5% of CD patients.35 A pediatric study from Japan demonstrated a family history of 3% for CD and 4% for UC.52 In Korea, an increase in the incidence of a positive family history from 1.3% in 2001 to 2.7% in 200513 paralleled the increased incidence of IBD suggesting that the low occurrence of a family history may be a reflection of the low population prevalence, and will change with time. Smoking.  Amongst all risk factors smoking represents one of the most consistently observed environmental influences on IBD.