irritable bowel syndrome ( ibs ) , as the most common functional gastrointestinal disorder ( fgid ) , is characterized by abdominal pain or discomfort and alteration of bowel habits and disordered defecation , in the absence of organic disease . despite the high prevalence of ibs in general population and the personal and economic costs , its etiology remains vastly unknown ; however , various studies have shown that several factors including abnormal motility of intestine , visceral hypersensitivity , inflammation , neurotransmitter imbalance , disturbance of brain - gut interaction , abnormal central processing , autonomic and hormonal events , and genetic , environmental , and psychosocial factors may contribute in incidence of ibs . it is believed that the incidence of ibs is more prevalent in women than in men and the age of its onset is in the range of 30 to 50 years . the prevalence of ibs varies across the world , ranging from as high as 9% to 22% in the united states and european countries , to as low as 4.2% and 4.4% in india and thailand , respectively , based on various diagnostic criteria.[35 ] it was reported that prevalence of ibs was 3 to 20 % in the north america . the prevalence of ibs was estimated to be 11 , 10.4 and 8.6% , respectively , by using manning , rome i , and rome ii criteria . such variation in these reports may be due to the difference in selected population in each study or even using different criteria in diagnosing ibs . recently , it has been observed that the prevalence of ibs is raising among asian communities . mahmoudi et al . determined it to be 4.2% based on rome i criteria . while pourshams et al . by employing rome ii criteria , reported that the prevalence of ibs in students of tehran university was 4.75% . the prevalence of ibs in 18180 people in five cities in tehran province was estimated to be about 1 % by employing iii criteria ; whereas ganji et al . by using rome ii diagnostic criteria , demonstrated that the prevalence of ibs in the city of tehran was about 25% and also claimed that ibs was the second most prevalent gastrointestinal disorder after gastroesophageal reflux disease in outpatients visiting gastrointestinal clinics . ibs has strong negative effect on quality of life in patients who suffer from it and it imposes substantial social and economic costs due to medical seeking behavior and absenteeism.[1520 ] in the united states , the direct and indirect cost of ibs has been estimated to be between 1.7 to 10 million dollars and 19.2 million dollars per year , respectively . one study in iran investigated the economic burden of ibs , and showed that the cost of ibs in iran is about 2.8 million dollars and this is of great significance for iranian population . to our knowledge , there has not been any review article in relation to the prevalence of ibs in iran until now . the aim of this study was to systematically review the articles about the epidemiology of ibs in iran , to discuss the limitations of current research on this subject and to make recommendations for future studies . in addition , this review provides background knowledge for the  study on the epidemiology of psychological , alimentary health and nutrition  ( sepahan ) . the data of sepahan will explore the epidemiology of fgids in isfahan province and it will be published later by the same study group . this is a systematic review of all published studies on the epidemiology of ibs in iran . studies that were used in the present review were primarily identified via searching in four online bibliographic databases including pubmed , google scholar , scientific information database and iranmedex . our pubmed search query was as follows : ( ibs[all fields ] or (  irritable bowel syndrome[mesh terms ] or  irritable bowel syndrome[all fields ] ) ) and  iran[all fields ] ) . review of the google scholar database was done using the following terms :  irritable bowel syndrome  ,  ibs  , and likewise , we used keywords like  irritable bowel syndrome  and  ibs  for searching relevant articles in the persian bibliographic databases ( www.sid.ir ) and iranmedex ( www.iranmedex.ir ) . in addition , manual search of reference lists from studies with relevant abstracts and recent reviews was carried out . search of all databases from inception to present was done and the last search was conducted on march 10 , 2012 . two investigators reviewed the titles and abstracts of all citations for eligibility criteria , to include the studies in the review . selected articles were studies that 1 ) had adult sample populations ; 2 ) reported the prevalence , incidence , or natural history of ibs ; and 3 ) was in full manuscript publication form . studies were excluded if they were conducted in various highly selected populations ( e.g. , patients with diabetes mellitus or pregnant women ) . eligible articles were investigated by two reviewers . to explore the prevalence of ibs in iran , information about gender distribution , their mean age and the reported prevalence were extracted from articles . data in relation to the first author , province and district of the study , diagnostic definition of ibs ( e.g. , manning criteria , rome i criteria ) , sampled population , sample size , and case ascertainment methods to identify ibs patients ( e.g. , face - to - face interviews , mail surveys ) were extracted too ( table 1 ) . studies that were used in the present review were primarily identified via searching in four online bibliographic databases including pubmed , google scholar , scientific information database and iranmedex . our pubmed search query was as follows : ( ibs[all fields ] or (  irritable bowel syndrome[mesh terms ] or  irritable bowel syndrome[all fields ] ) ) and  iran[all fields ] ) . review of the google scholar database was done using the following terms :  irritable bowel syndrome  ,  ibs  , and likewise , we used keywords like  irritable bowel syndrome  and  ibs  for searching relevant articles in the persian bibliographic databases ( www.sid.ir ) and iranmedex ( www.iranmedex.ir ) . in addition , manual search of reference lists from studies with relevant abstracts and recent reviews was carried out . search of all databases from inception to present was done and the last search was conducted on march 10 , 2012 . study selection criteria . two investigators reviewed the titles and abstracts of all citations for eligibility criteria , to include the studies in the review . selected articles were studies that 1 ) had adult sample populations ; 2 ) reported the prevalence , incidence , or natural history of ibs ; and 3 ) was in full manuscript publication form . studies were excluded if they were conducted in various highly selected populations ( e.g. , patients with diabetes mellitus or pregnant women ) . eligible articles were investigated by two reviewers . to explore the prevalence of ibs in iran , information about gender distribution , their mean age and the reported prevalence were extracted from articles . data in relation to the first author , province and district of the study , diagnostic definition of ibs ( e.g. , manning criteria , rome i criteria ) , sampled population , sample size , and case ascertainment methods to identify ibs patients ( e.g. , face - to - face interviews , mail surveys ) were extracted too ( table 1 ) . details of the search in electronic databases are presented in figure 1 . searching pubmed and google scholar led us to 10 and 24 further suitable articles , respectively . in addition , fourteen relevant studies were found using scientific information database and iranmedex . after excluding several articles by reading their full texts , 28 articles remained and we applied them in our study . however , 5 of them were found to be duplicate studies.[132528 ] three of the identified studies were conducted in highly selected populations,[2931 ] and in two articles , studied popula - tions were adolescents . consequently , after final evaluation and considering the overlapping articles which were found in different databases , 18 articles were included in the systematic review.[1012143234434547 ] characteristics of the reviewed articles ( first author , place of study , study population , sample size , definition criteria , gender distribution , mean age of population , and ibs prevalence ) are summarized in table 1 ( dissimilarities in methodology were not taken into consideration ) . diagram of the searches for articles to be included in the systematic review of irritable bowel syndrome in iran the earliest study was published in 1997 , in which manning criteria were employed for diagnosing ibs patients . ten studies were conducted in tehran province.[1012143841424547 ] two studies were conducted in northern provinces of iran , three in the west[3436 ] and three studies were performed in fars province which is located in south of iran . the majority of studies used rome ii criteria to diagnose ibs.[11143437394042434547 ] manning , rome i and rome iii criteria were also employed . in a study carried out by yarandi et al . subjects were diagnosed with ibs by fulfilling either rome ii or rome iii criteria . in one study , no definition criteria were mentioned and patients were diagnosed with ibs after ruling out organic conditions . in eleven of the fourteen studies that presented the data by gender , a significant correlation between gender and ibs was observed . in 9 studies , there was marked female predilection,[10123739424345 ] but male preponderance was described only by two studies . re - ported that ibs was more prevalent among males ( 20.2% vs. 8.2% ) . likewise , bagheri lankarani et al . found that the prevalence of ibs in women was higher than in men ( 17.3% vs. 13% ) ; however , the difference was not statistically significant . in another study , the of femalemale ratio of ibs patients was 2.5:1 ( 1.5% versus 0.6% ) . hatami et al . reported that prevalence of ibs in individuals older than 55 years was less than those who were younger ; however , this difference was not statistically significant . in ghannadi 's study , ibs was more prevalent in 1 and 2 year compared to 4 and 5 year medical students . this finding can be due to the students adaptation to a new environment with difficult situations and the effect of this factor on their health . however , in another study in shiraz , the prevalence of ibs increased with advancing age among medical students . there was also a significantly increased prevalence of ibs in 4 year students , and the least prevalence was noted among 1 year students ( 26% vs. 9.6% ) . overall , it seems that there is a minimal difference in ibs prevalence within different age groups . only three studies reported the prevalence of ibs by its subtypes . in a study conducted in golestan university of medical sciences in 2005 - 6 , individuals meeting the rome ii criteria for ibs were further divided into subgroups based on their bowel symptoms . in this study , 81.6% of patients were affected by constipationpredominant ibs , 6.1% had diarrhea - predominant ibs , and 12.2% did not meet the criteria for either constipation or diarrhea sub - type . showed that of individuals with ibs , 50% had constipation - predominant ibs and 29% fulfilled the criteria for diarrhea - predominant ibs . additionally , in this study 21% of subjects suffered from both constipation and diarrhea alternatively . hatami et al . found that 20.1% , 15% , and 7.2% of ibs patients suffered from diarrhea - predominant , constipation - predominant , and alternating subtype , respectively . the reported prevalence of ibs ranged from a low of 1.1% to a high of 25% . in the only study that used manning criteria , the lowest prevalence of ibs that reported in iran was 1.1% . in this study , rome iii criteria were used in 18180 individuals who living in four cities of tehran province plus a small part of tehran ( including countrysides and rural areas ) . they employed rome ii criteria , and reported the prevalence of ibs in outpatients visiting a gastrointestinal clinic in tehran was 25% . details of the search in electronic databases are presented in figure 1 . searching pubmed and google scholar led us to 10 and 24 further suitable articles , respectively . in addition , fourteen relevant studies were found using scientific information database and iranmedex . after excluding several articles by reading their full texts , 28 articles remained and we applied them in our study . however , 5 of them were found to be duplicate studies.[132528 ] three of the identified studies were conducted in highly selected populations,[2931 ] and in two articles , studied popula - tions were adolescents . consequently , after final evaluation and considering the overlapping articles which were found in different databases , 18 articles were included in the systematic review.[1012143234434547 ] characteristics of the reviewed articles ( first author , place of study , study population , sample size , definition criteria , gender distribution , mean age of population , and ibs prevalence ) are summarized in table 1 ( dissimilarities in methodology were not taken into consideration ) . diagram of the searches for articles to be included in the systematic review of irritable bowel syndrome in iran the earliest study was published in 1997 , in which manning criteria were employed for diagnosing ibs patients . ten studies were conducted in tehran province.[1012143841424547 ] two studies were conducted in northern provinces of iran , three in the west[3436 ] and three studies were performed in fars province which is located in south of iran . the majority of studies used rome ii criteria to diagnose ibs.[11143437394042434547 ] manning , rome i and rome iii criteria were also employed . in a study carried out by yarandi et al . subjects were diagnosed with ibs by fulfilling either rome ii or rome iii criteria . in one study , no definition criteria were mentioned and patients were diagnosed with ibs after ruling out organic conditions . in eleven of the fourteen studies that presented the data by gender , a significant correlation between gender and ibs was observed . in 9 studies , there was marked female predilection,[10123739424345 ] but male preponderance was described only by two studies . re - ported that ibs was more prevalent among males ( 20.2% vs. 8.2% ) . likewise , bagheri lankarani et al . found that the prevalence of ibs in women was higher than in men ( 17.3% vs. 13% ) ; however , the difference was not statistically significant . in another study , the of femalemale ratio of ibs patients was 2.5:1 ( 1.5% versus 0.6% ) . hatami et al . reported that prevalence of ibs in individuals older than 55 years was less than those who were younger ; however , this difference was not statistically significant . in ghannadi 's study , ibs was more prevalent in 1 and 2 year compared to 4 and 5 year medical students . this finding can be due to the students adaptation to a new environment with difficult situations and the effect of this factor on their health . however , in another study in shiraz , the prevalence of ibs increased with advancing age among medical students . there was also a significantly increased prevalence of ibs in 4 year students , and the least prevalence was noted among 1 year students ( 26% vs. 9.6% ) . overall , it seems that there is a minimal difference in ibs prevalence within different age groups . only three studies reported the prevalence of ibs by its subtypes . in a study conducted in golestan university of medical sciences in 2005 - 6 , individuals meeting the rome ii criteria for ibs were further divided into subgroups based on their bowel symptoms . in this study , 81.6% of patients were affected by constipationpredominant ibs , 6.1% had diarrhea - predominant ibs , and 12.2% did not meet the criteria for either constipation or diarrhea sub - type . showed that of individuals with ibs , 50% had constipation - predominant ibs and 29% fulfilled the criteria for diarrhea - predominant ibs . additionally , in this study 21% of subjects suffered from both constipation and diarrhea alternatively . hatami et al . found that 20.1% , 15% , and 7.2% of ibs patients suffered from diarrhea - predominant , constipation - predominant , and alternating subtype , respectively . the reported prevalence of ibs ranged from a low of 1.1% to a high of 25% . in the only study that used manning criteria , the lowest prevalence of ibs that reported in iran was 1.1% . in this study , rome iii criteria were used in 18180 individuals who living in four cities of tehran province plus a small part of tehran ( including countrysides and rural areas ) . they employed rome ii criteria , and reported the prevalence of ibs in outpatients visiting a gastrointestinal clinic in tehran was 25% . details of the search in electronic databases are presented in figure 1 . searching pubmed and google scholar led us to 10 and 24 further suitable articles , respectively . in addition , fourteen relevant studies were found using scientific information database and iranmedex . after excluding several articles by reading their full texts , 28 articles remained and we applied them in our study . however , 5 of them were found to be duplicate studies.[132528 ] three of the identified studies were conducted in highly selected populations,[2931 ] and in two articles , studied popula - tions were adolescents . consequently , after final evaluation and considering the overlapping articles which were found in different databases , 18 articles were included in the systematic review.[1012143234434547 ] characteristics of the reviewed articles ( first author , place of study , study population , sample size , definition criteria , gender distribution , mean age of population , and ibs prevalence ) are summarized in table 1 ( dissimilarities in methodology were not taken into consideration ) . diagram of the searches for articles to be included in the systematic review of irritable bowel syndrome in iran the earliest study was published in 1997 , in which manning criteria were employed for diagnosing ibs patients . ten studies were conducted in tehran province.[1012143841424547 ] two studies were conducted in northern provinces of iran , three in the west[3436 ] and three studies were performed in fars province which is located in south of iran . the majority of studies used rome ii criteria to diagnose ibs.[11143437394042434547 ] manning , rome i and rome iii criteria were also employed . in a study carried out by yarandi et al . subjects were diagnosed with ibs by fulfilling either rome ii or rome iii criteria . in one study , no definition criteria were mentioned and patients were diagnosed with ibs after ruling out organic conditions . in eleven of the fourteen studies that presented the data by gender , a significant correlation between gender and ibs was observed . in 9 studies , there was marked female predilection,[10123739424345 ] but male preponderance was described only by two studies . re - ported that ibs was more prevalent among males ( 20.2% vs. 8.2% ) . likewise , bagheri lankarani et al . found that the prevalence of ibs in women was higher than in men ( 17.3% vs. 13% ) ; however , the difference was not statistically significant . in another study , the of femalemale ratio of ibs patients was 2.5:1 ( 1.5% versus 0.6% ) . hatami et al . reported that prevalence of ibs in individuals older than 55 years was less than those who were younger ; however , this difference was not statistically significant . in ghannadi et al . 's study , ibs was more prevalent in 1 and 2 year compared to 4 and 5 year medical students . this finding can be due to the students adaptation to a new environment with difficult situations and the effect of this factor on their health . however , in another study in shiraz , the prevalence of ibs increased with advancing age among medical students . there was also a significantly increased prevalence of ibs in 4 year students , and the least prevalence was noted among 1 year students ( 26% vs. 9.6% ) . overall , it seems that there is a minimal difference in ibs prevalence within different age groups . only three studies reported the prevalence of ibs by its subtypes . in a study conducted in golestan university of medical sciences in 2005 - 6 , individuals meeting the rome ii criteria for ibs were further divided into subgroups based on their bowel symptoms . in this study , 81.6% of patients were affected by constipationpredominant ibs , 6.1% had diarrhea - predominant ibs , and 12.2% did not meet the criteria for either constipation or diarrhea sub - type . showed that of individuals with ibs , 50% had constipation - predominant ibs and 29% fulfilled the criteria for diarrhea - predominant ibs . additionally , in this study 21% of subjects suffered from both constipation and diarrhea alternatively . hatami et al . found that 20.1% , 15% , and 7.2% of ibs patients suffered from diarrhea - predominant , constipation - predominant , and alternating subtype , respectively . the reported prevalence of ibs ranged from a low of 1.1% to a high of 25% . in the only study that used manning criteria , the lowest prevalence of ibs that reported in iran was 1.1% . in this study , rome iii criteria were used in 18180 individuals who living in four cities of tehran province plus a small part of tehran ( including countrysides and rural areas ) . they employed rome ii criteria , and reported the prevalence of ibs in outpatients visiting a gastrointestinal clinic in tehran was 25% . according to the 18 epidemiological studies that were included in the present systematic review , the prevalence of ibs in iran varied from 1.1% to 25% . an important factor that should be taken into account is the use of different diagnostic criteria for ibs . as previously mentioned , manning criteria was employed only in one study , and the majority of iranian studies used different versions of rome criteria . for instance , mahmoudi et al . reported that the prevalence of ibs among 3008 students of tehran university was 4.2% , based on rome i criteria . however , another study in this population using rome ii criteria reported a prevalence of 4.75% . in one study in new zealand , the reported prevalence of ibs based on manning 2 , manning 3 , rome i , and rome ii criteria was 16.2% , 9.7% , 5.6% , and 5.1% , respectively . in another study in korea , the prevalence of ibs was 8% and 9% based on rome ii and rome iii criteria , respectively . authors of this study concluded that the rome iii criteria are less restrictive and they have fine agreement with the rome ii criteria . since rome ii criteria demand patients to report their symptoms over a longer period comparing to the rome iii , a higher number of patients will be diagnosed with ibs using rome ii . the majority of iranian studies were conducted before rome iii criteria were proposed and only three studies used rome iii criteria . differences in sampled population may be another reason for the wide range of reports on the prevalence of ibs in iran . for instance , hatami et al . determined the prevalence of ibs among blood donors in tehran . the role of differences in socioeconomic status and cultural differences should be also taken into account . it is believed that the prevalence of ibs is less in developing countries compared to western countries . prevalence of ibs in iranian studies was different between females and males . based on these studies , the prevalence of ibs in women was 1.5 - 17.3% , while in men it was 0.6 - 20.2% . more than half of reviewed studies in the present systematic review demonstrated that prevalence of ibs has statistically significant correlation with gender;[10123639424347 ] but four studies were the opposite . similarly , in india , ibs was reported to be more prevalent in men than in women . in a study in bangladesh worldwide , most studies especially those conducted in western countries showed that ibs affects women more than men . the majority of studies performed in iran showed that there was no relation between age and prevalence of ibs . khademolhosseini et al . reported that the prevalence of ibs was higher in the range of 33 to 45 yeas old . several studies which carried out in other countries reported that the prevalence of ibs decreases with age.[5962 ] since most of the included studies were not population - based , we were not able to conclude in which age group ibs was more or less prevalent . in iranian studies , no relation was found between prevalence of ibs and educational level . worldwide studies on this issue presented controversial results.[86365 ] there was no relation between marital status and ibs in iran . only one study reported that married subjects were more likely to have ibs compared to singles , widows or divorced individuals . moghimi dehkordi et al . estimated the total 6-month cost of iranian ibs patients to be about ppp$160 ( purchasing power parity dollars ) . ibs patients had the highest percentage of drug consumption and the duration of their absence from work was higher ( 2.26 days ) in comparison with other fgid patients . until now in addition , there are not enough population - based studies in order to assess the epidemiological aspects of ibs in iran . estimated prevalence of ibs in iran has a wide range . since there is not enough literature on the incidence and natural history of ibs in iranian population , efforts should focus on developing well - designed studies to investigate the epidemiology of irritable bowel syndrome and ideally , these studies should be community based . because of the high prevalence of ibs and its considerable economic burden on iranian population , researchers should concentrate on etiology of ibs and try to plan preventive programs in future studies .
objectives : irritable bowel syndrome ( ibs ) is a common gastrointestinal disorder . due to its high prevalence and absence of curative therapy 
 , ibs has the potential to create tremendous burden on the health care system . 
 herein , we systematically reviewed the published literature to investigate the epidemiology of ibs in iran.methods:studies that were reviewed in this article were primarily identified through four online bibliographic databases including pubmed , google scholar , iran medex , and scientific information database . 
 manual search of reference lists was carried out to identify any additional studies such as relevant abstracts and also recent review articles which may have been missed . 
 potentially related studies were retrieved and the selection criteria were applied . 
 eligible articles were reviewed.results:from 4176 studies identified , 18 eligible studies were included . 
 it was reported that in iran , the prevalence of ibs was in the range of 1.1% to 25% and was more common in women . 
 in addition , the difference in frequency of different age groups was minimal . there was a minimal difference in ibs prevalence within different age groups.conclusions:in iran , the incidence of ibs was in the wide range . since there are not enough population - based studies , researchers should focus on developing well - designed population - based studies to determine the epidemiology of ibs in iran 
 . 
 moreover , cohort studies should be conducted in order to investigate the natural history of ibs . 
 investigating the etiology of ibs and attempt to organize health promotion programs are highly suggested .