The current prevalence of irritable bowel syndrome in Asia.

Irritable bowel syndrome (IBS) has been one of the commonly presented gastrointestinal disorders. It is of interest how commonly it presents in the society. Western studies indicated that most population-based IBS prevalences range 10%-15%. It is believed that IBS is prevalent in both East and West countries without a significant prevalence difference. Most recently, the Asia IBS prevalence has a higher trend in the affluent cities compared to South Asia. Since many Asia IBS prevalence studies have been published in the recent decade, we could compare the IBS prevalence data divided by various criteria in looking whether they were also comparable to this of West community. Summarized together, most Asia community IBS prevalences based on various criteria are usually within the range 1%-10% and are apparently lower than these of selected populations. Within the same population, the prevalence orders are first higher based on Manning criteria, then followed by Rome I criteria and finally reported in Rome II criteria. Overall, the median value of Asia IBS prevalences defined by various criteria ranges 6.5%-10.1%. With regard to gender difference, female predominance is usually found but not uniquely existed. For the IBS subtypes, the proportions of diarrhea predominant-IBS distribute widely from 0.8% to 74.0%, while constipation predominant-IBS proportion ranges 12%-77%. In conclusions, current Asia IBS prevalence is at least equal to the Western countries. Female predominant prevalence in Asia is common but not uniquely existed, while the proportions of IBS subtypes are too variable to find a rule.

Introduction

Upon Rome III definition, irritable bowel syndrome (IBS) has been a biopsychosocial dysfunction. It means that a biological bowel dysfunction is the final result of brain-gut linkage and modified by the social, environmental and psychological factors.1,2 Since a well-known functional disorder usually coexisted with other somatic complaints, IBS per se has an obvious impact on living and quality of life of sufferers leading to the excessive social costs for medical seeking behavior and absenteeism.3-9 Today, IBS has been included as one of the commonly presented functional gastrointestinal disorders (FGIDs).1 It is of interest how commonly it presents in the society. In addition, knowing the IBS prevalence may estimate how it would consume the limited medical resources in the society. Western studies indicated that the population-based IBS prevalence widely ranges between 3%-20%, whereas the most reported data range from 10% to 15%.10,11 It draws a controversy why the IBS prevalence studies usually show an obvious discrimination. Actually, most prevalence study obtained data completely depend upon the response of distributed questionnaires to the studied subjects. Thereafter, the demographic characteristics in terms of evaluated population, willing of responsiveness, geographical location, criteria to define, etc always individually exist leading to the study heterogeneity and variation in the reported IBS prevalences.12-14 Of them, the employed IBS diagnostic criteria may obtain extremely distinct results for the same population. For example, Manning definition often yields a higher value compared to this of either Rome I or II definition with a gap of 2-5 folds or 2.5%-37.0%.4,14 Even confined to the Manning definition, the number of used disorders results in different values.14 In addition, large-scaled and questionnaire-based prevalence study does not exclude the alarm symptoms and the obtained results are unlikely to reflect the true IBS manifestations seen clinically.4,15,16 Since a characteristically biopsychosocial disorder, many social and cultural factors indeed have an apparent impact on the meaning, expression and course of FGIDs including IBS.17 Accordingly, gender,18-22 age,23,24 economic state,24-31 education level,24-29 married state,25,28,31 food,29-32 race,33 stress,21,22,28,31,34-36 climate,29,31 drugs,35 dysentery history29,35 and coexisted dyspepsia37 etc all have been addressed to be the risk factors leading to IBS.

Unfortunately, it is very hard to define that all enrolled study populations throughout the world should be harmonized with a least heterogeneity. Thus obtained IBS prevalences throughout the world would be quite variable among the studies. Besides, it is unknown whether these mentioned factors are truly existed because prevalence studies do not attempt to confirm their existence. Even some studies indicate the contradictory impact on the IBS. For instance, the same questionnaire applied to different countries may obtain the very dissimilar prevalence results, such as this conducted in Thailand and Western countries,38 another conducted in USA and 8 European countries39,40 and an early study carried out in Japan and The Netherlands,41 respectively. With regard to the IBS prevalence around the world, it has been indicated that the IBS prevalence is lower in non-western countries.17 In addition, a study based on Manning criteria indicated that the IBS prevalence of USA Asian residents was lower compared to others.42 However, this early statement meets challenge. Likewise, IBS prevalence is reported as higher as 26%-33% in the selected populations of the African countries.23,43 Similarly, the Japanese IBS prevalence was almost 3-fold of this of Dutch using the same questionnaire.41 Kang44 compared East IBS prevalences to those of West counterparts and provided the median values of 12% vs 17% in Manning criteria, 10.4% vs 9.2% in Rome I and 7.6% vs 6.0% in Rome II, respectively. He finally concluded no convincing prevalence difference existed in the East and West countries. In the same year, Gwee et al45 believed that the IBS prevalence is increasing among the Asia countries with the estimated community prevalence ranging 5.7%-8.6%, whereas these of selected population reach up to 16%-45%. Most recently, he reviewed the Asia IBS studies and indicated that the Asia IBS prevalence has a trend of higher in the affluent cities compared to South Asia, eg, 8.6%-9.8% vs 4.2%.46 Talley4 also pointed out that IBS is prevalent in both East and West countries without necessarily to emphasize on the prevalence difference. With regard to study IBS prevalence, employed criteria should be considered since it may produce enormously different results.47,48 While the proportions of IBS subtypes may not correlate well between the used criteria.49,50 Nevertheless, it is believed that no consistent differences in sensitivity and specificity between various criteria to diagnose IBS clinically.51 Very recently, many Asia IBS prevalence studies have been published within this decade. Now we could compare the IBS prevalence data divided by various criteria in looking whether they were also comparable to this of West community.

Community Population Based IBS Prevalences of Western Developed Countries

Hungin et al40 had conducted a large-scaled study that evenly enrolled population sizes of UK, 5999; France, 5033; Germany, 5002; Italy, 5082; Holland, 5463; Belgium, 5229; Spain, 5097 and Switzerland, 5079, respectively. Their study indicated that the recommended Rome criteria obtained a value less than 5%, whereas the extreme variation of prevalence values among enrolled countries still existed, eg, 11.7% in Italy and only 1.7% in German. Besides, Manning criteria defined IBS prevalence was higher compared to those of 2 Rome definitions within the same population. In order to know what is the most reported population based IBS prevalence, Table 1 illustrates 25 community-based IBS prevalences of Latin America and Western developed countries ranging from Europe, North America to Australia. Overall, 5 of 11 Manning and other criteria defined prevalence data are less than 10.5%, whereas remaining 6 values are higher than this point. In addition, 14 of 21 Rome defined prevalences are within the range 2%-10%, whereas another 7 prevalence data are higher than 10% particularly a Canadian study based on small sample size.18 Secondly, Manning criteria based studies usually report a higher prevalence than this of Rome definition within the same population. Thirdly, the same country using the same criteria may obtain different values among various enrolled community populations. Fourthly, small-scale study often results in a higher IBS prevalence even based on community population. Finally, female predominance is invariably found no matter of used IBS definitions.

Table 1

Community Population Based Prevalences of Irritable Bowel Syndrome Among the Western Developed Countries and Latin America

X2, 2 diagnostic statements; X3, 3 diagnostic statements; M/F, male/female; ND, no data; NM, not mentioned; NS, not significant.

IBS Prevalences of Asia Countries

Table 2 provides 11 IBS prevalence data of Asia countries. Of them, 6 were based on Manning definition, whereas 5 did not mention their employed definitions. Most reported prevalences are within the range 2.3%-11.5% but a Japanese study based on selected population obtained a higher value.41 Apart from other definitions, the median value of 6 Manning based studies is 10%. Female predominance is found but not always existed. Based on Rome I criteria definition, Table 3 depicts 8 Asia IBS prevalence data plus another Korea study from Rome α definition. Many of them were conducted in East Asia. The range of 4 community population based prevalences is within 0.82%-10.4%, whereas the data of 5 selected population studies are variable from overlapping to much higher. The median value of 8 Rome I definition based studies is 6.5%. Female predominance remains existed. Rome II criteria based prevalence has been extensively reported in Asia, Table 4 provides 35 IBS prevalence values obtained as far as from Turkey to the most Eastern Asia countries such as Japan and Korea. Overall, 14 of 16 community population based prevalences are within 2.9% and 10.2%, whereas another 2 values are higher up to about 14.0%.82,86 With regard to 19 data of selected population studies, only 7 values are less than 10.0%, whereas other 12 higher values even reach up to 31.0%.97 Overall, the median value of 35 Rome II definition based studies is 8.6%. Regarding the gender difference based on Rome II criteria, 22 of 31 studies reported a female predominance, whereas 5 reported male predominance and 4 reported almost equally distributed. Table 5 provides 9 Rome III criteria defined IBS prevalence data among the Asia countries. Two West Asia community-based studies indicate the values of 1.1% and 11.4%, respectively.26,101 A Korea community study provides prevalence of 9.0%,98 whereas 6 selected population based studies are very variable ranging 7.0%-21.9%. The median value of 9 Rome III definition based studies is 10.1%. Female predominance is also found among 7 reports.

Table 2

Prevalences of Manning and Other Criteria Defined Irritable Bowel Syndrome in Asia Countries

M/F, male/female; ND, no data; NM, not mentioned.

Table 3

Prevalences of Rome I and α Criteria Defined Irritable Bowel Syndrome in Asia Countries

M/F, male/female; ND, no data; NM, not mentioned.

Table 4

Prevalences of Rome II Criteria Defined Irritable Bowel Syndrome in Asia Countries

M/F, male/female; ND, no data; NM, not mentioned; NS, not significant.

Table 5

Prevalences of Rome III Defined Irritable Bowel Syndrome in Asia Countries

M/F, male/female; NM, not mentioned.

Summarized together, the reported IBS prevalences of Tables 2-5 are very variable with a range 0.82%-31.0% among the Asia countries. However, these data are likely to indicate that the most Asia community prevalences are within the range 1%-10% and lower than these of selected populations as well as previous comments.45,105,106 Similar to Table 1, the same country using the same criteria usually yields dissociated results among the different study populations. On the other hand, the same population always results in different prevalences defined by various criteria. Within the same population, the prevalence orders are usually first higher based on Manning criteria, then followed by Rome I criteria and finally reported in Rome II criteria. This ranking characteristic is also to agree with Asia consensus.106 Occasionally, few studies in Asia and developed countries contradictorily indicated the higher value based on Rome II than Rome I.34,75 With regard to Rome III criteria, it is apparently higher than Rome II reported in Israeli, Chinese and Korean studies, respectively,26,90,95 whereas another study carried out in a selected Chinese population showed comparable in both definitions.89,102 In contrast, an Iran study yields a much lower prevalence by way of Rome III criteria.101 Most importantly, the IBS prevalence studies conducted on multi-ethnic countries such as Malaysia and Singapore clearly pointed out no difference existed among various ethnic populations.24,36,70,86 Similarly, the IBS prevalence of Chinese minority was not different from this of Han ethnic.31 Based on these observations and comparisons, we as well as the Asia consensus106 are strongly to conclude that the current Asia IBS prevalence is at least equal to the Western countries.

Gender Difference of Asia Countries

Gender factor may play an impact on the FGIDs including IBS. As previously indicated that female gender has been one of factors leading to IBS and females usually report more FGID symptoms.63 Perhaps it means that the visceral perception is determined by the sex.17 Female IBS subjects also have lower authority over decisions at work.107 Besides, Caucasian females easily suffer from IBS symptoms compared to males or African American females.33 Based on the current IBS diagnostic criteria, higher positive predictive value is often obtained for females, whereas a negative predictive value exists for males.108 Accordingly, it is unknown whether these gender-related specificities account for the female predominance in many IBS studies. Clinically, constipation predominant IBS (C-IBS) is commonly seen among the females, whereas males usually manifest diarrhea-predominant IBS (D-IBS).19,25,90,109,110 In addition, IBS is common among the Vietnamese females but no significant gender effect on some bowel symptoms in terms of stool frequency, consistency and bloating is observed.73 Table 1 depicts the IBS male/female ratio among the developed countries. Almost all except a USA study indicate the female predominance, irrespectively of used criteria.60 Interestingly, a Finnish study showed female predominance in Manning definition and gradually became equal in Rome II definition.14 For the African IBS, female predominance is not reported yet.23,43 Regarding the Asian IBS gender issue, Gwee et al45 early pointed out lack of female predominance except the existed female predominance in Japan. Recent Asia IBS consensus also concludes no obvious female predominance existed in many Asia studies.106 Tables 2-5 provide the sex ratios among cited Asia studies. The ratios are widely variable ranging from equal to 2-fold of female predominance. Even the same country may not obtain the similar gender ratio among various reports, eg, Pakistan, Singapore, China and Korea, respectively. Accordingly, the female predominance looks to be commonly existed in Near East, Bangladesh, Southeast Asia, China, Japan and finally some but not all Korea studies, whereas the remaining countries just show similar or diverse ratio. With regard to the used criteria, a Korea study indicates that female subjects showed a higher prevalence than male subjects under Rome III but not under Rome II criteria.95 Summarized together, the IBS female predominance is not uniquely existed among all Asia countries.

Subtypes of IBS in Asia

The IBS subtypes are mainly divided according to the bowel movement (BM) frequency and stool consistency of the presenting subjects. Consequently, it looks important to know what is the so-called normal bowel habit in the general population. Among the Asia countries, many studies already provide the BM parameters. For instance, subjects with non-complaint of lower abdomen symptoms in India usually have the BM as 1-2 times/day.69 Over 90% people of Thailand and Singapore have the BM as 3 times/day to 3 times/wk, while nearly 60% of them pass once daily.38,70 Koreans also exhibit this BM pattern and 41% of them report once daily.30 Meanwhile, 84% Chinese non-patient community subjects report BM once daily with a mean value 7 times/wk. Besides, 90% of them pass formed soft stool, 77% finish it in the morning and only 3.8% show constipation and 1.1% as diarrhea, respectively.111 It can be concluded that the BM ranging 3 times/day to 3 times/wk is acceptable as normal for most Asia people.

Regarding the IBS subtypes, this subjective category remains difficult in clinical practice. Because the restrictive character of Rome II definition and alternating-IBS (A-IBS) being really unknown as part of C- or D-IBS, most IBS are perhaps undiagnosed.12,39 Surprisingly, even some A-IBS subjects think that their BM is normal despite the alternating expression.24 Thereafter, who such as physician or patient himself or what criteria should determine the subtype correctly? In addition, IBS subtypes are likely depending upon heterogeneity in terms of evaluated population, gender, geographical location and criteria to define.12,19,22,40,44,90,108,110 For example, the subtype correlation between Rome II and III has been poor because the apparently existed drawback in the categories of A-IBS, mixed-IBS and unsubtyped-IBS, respectively.49,90 Finally, a review indicates that USA population-based studies found similar distribution of C-IBS, D-IBS and A-IBS, whereas European studies showed either C-IBS or A-IBS as the most prevalent subtypes. More interestingly, primary care office-based studies showed A-IBS as the most prevalent group, while the specialist office-based studies found either C-IBS or D-IBS as the most frequently reported subtype.12 It is likely the different attitude to acknowledge IBS between primary care and gastroenterologists. For example, not more than 50% of primary care physicians could reach the consensus, while cultural differences in the description of key symptoms is responsible for this discrimination.112 Table 6 depicts the percentile distribution of IBS subtypes in 12 Western and 28 Asian countries. Among the developed countries, there is quite variable in the distribution of 3 main subtypes. Apart from Manning definition, it looks that the subtype proportions of C-IBS and D-IBS usually range 15%-55%, whereas this of A-IBS ranges higher as 20%-65%. The subtype correlation between Rome I and II is optimal but is not well existed between Rome II and III. For the Asian countries, the proportions of D-IBS distribute widely from 0.8% to 74.1%, C-IBS proportion ranges 12.0%-77.4%, whereas A-IBS appears less common with range 6.7%-49.0%. Of 8 Rome III criteria based studies showing subtypes, 5 report unsubtyped-IBS with proportion ranged 12.1%-32.7%. Apart a Korea study,95 the subtype correlation between Rome II and III is poor as well as this of Western studies. Summarized together, IBS subtype proportions are very variable among the Asia studies. It is likely to mean that the clear and precise differentiation of various subtypes to fit BM stool form and occupied duration remains very subjective both for the patients and physicians themselves.

Table 6

Percentile Distribution of Reported Subtypes in Subjects With Irritable Bowel Syndrome

aCommunity based study.

X2, 2 diagnostic statements; X3, 3 diagnostic statements; IBS, irritable bowel syndrome; D-IBS, diarrhea predominant-IBS; C-IBS, constipation predominant-IBS; A-IBS, alternating-IBS; M-IBS, mixed-IBS; U-IBS, un-subtyped-IBS; NM, not mentioned.

In conclusions, current Asia IBS prevalence is at least equal to the Western countries. Female predominant prevalence in Asia is common but not uniquely existed, while the proportions of IBS subtypes in Asia are too variable to find a rule.