Abdominal bloating is the most bothersome symptom in irritable bowel syndrome with constipation (IBS-C): a large population-based Internet survey in Japan

We conducted a large-scale Internet survey investigating 30,000 adults from the general public throughout Japan. In this study, we estimated frequencies of the subtypes of IBS using the Rome III diagnostic questionnaire [16, 17], and then investigated what is the most bothersome symptom and what factors in the daily life exaggerate the dominant symptoms among subjects with IBS-C. As long as we know, this is the first report on a large number of subjects diagnosed as IBS-C demonstrating that the degree of anxiety in their daily lives is not always associated with frequency of bowel movement. Furthermore, we also found that the most bothersome symptom, abdominal bloating, occurs most often after meal, subsequently at work or school and during time of stress in subjects with IBS-C.

The sensation of abdominal bloating may affect 10 to 30 % of healthy subjects and up to 96 % of patients with IBS [9]. Abdominal bloating is more often noted by females with IBS than males, with symptoms increasing in relation to menses [18]. Abdominal bloating is associated with decreased QOL and may cause a higher number of physician visits [19]. Indeed, the IBS symptom severity scale (IBS-SSS) [20], which is widely used to assess the severity of IBS, consists of the item on the severity score for abdominal bloating as well as abdominal pain. However, the presence of abdominal bloating in other functional GI disorders and even in healthy subjects [19] means that it is not necessarily considered a diagnostic criterion for IBS.

‘Abdominal bloating’ is not always a specific term that implies both to the subjective sensation and to the objective or ‘visible’ abdominal distention [21]. In the present study, the symptom descriptions in Japanese, ‘abdominal bloating’, ‘abdominal distention’, ‘sensation of excessive gas’, ‘tightness in the abdomen’ and ‘abdominal fullness’ were used as independent symptomatic items on the main questionnaire. In our findings, the most common symptom of these 5 terms which IBS subjects expressed during constipation was abdominal bloating and the fewest was abdominal fullness (see Table 3).

Previous findings of abdominal girth using plethysmography [21, 22] may support our results of different frequencies of abdominal bloating and distention in subjects with IBS-C. Using this technique it has been demonstrated that most patients who have abdominal distention also report abdominal bloating and that patients with bloating alone have lower sensory thresholds in the rectum compared to healthy subjects, whereas those with abdominal bloating and distention have normal or slightly higher sensory thresholds [21]. On the other hand, it has been reported that increase in abdominal girth in a day directly correlated with orocecal and colonic transit times, and inversely with stool consistency [22]. Therefore, abdominal bloating alone may be more reflection of visceral hypersensitivity, whereas abdominal bloating with distension may be more of a peripheral physiological problem.

In our subjects with IBS-C, the degree of anxiety in their daily lives was associated with severity of abdominal pain, discomfort and bloating, but not with frequency of bowel movement. It has been demonstrated that IBS patients feel more stress which may exaggerate IBS symptoms such as abdominal pain compared to healthy subjects [5]. In patients with IBS, psychological or physiological stimulus (i.e., stress) alters both visceral perception (mostly, hypersensitivity) [23‐25] and colonic motility (mostly, hypercontractility even in IBS-C) [26, 27]. However, it has been reported that only 11.5 % of patients with IBS-C showed delayed colonic transit [11]. In addition, no relationship has been detected between stress factors and colonic transit in IBS patients [28]. These findings suggest that lower frequency of bowel movement in IBS-C may not always reflect inhibition of bowel movement by stress.

IBS patients often relate their symptoms to the intake of certain foods. IBS symptoms such as abdominal pain and bloating occur or are exacerbated postprandially in approximately two-thirds of patients [3, 4]. We have previously reported that female subjects with IBS had more irregular meals and skipped meals more frequently compared to non-IBS subjects in nursing and medical school students [29]. Furthermore, IBS patients showed an exaggerated sensory component of the gastrocolonic response, expressed as lowered colonic perception thresholds and increased viscerosomatic referral area for abdominal pain after duodenal lipid infusion [30]. On the other hand, an intestinal transit study using scintigraphy revealed that IBS-C patients showed normal ileocolonic transit but somewhat delayed colonic transit in response to meal ingestion [31]. We have also demonstrated that meal ingestion did not induce altered colonic motility response in patients with IBS-C [27]. Therefore, exaggerated abdominal boating in IBS-C subjects after the meals in this study may be due to increased visceral perception, increased gut contractions and impaired propulsive movement in response to the nutritions.

A limitation of our study was to use the Internet-based survey. Subjects who were interested in own health might be more likely to participate in this survey. In the present study, 30,000 samples were collected from the large monitor panel throughout Japan and set same numbers of sex and several aged group flames. Therefore, we believe ascertainment bias is unlikely because the prevalence of overall IBS and IBS-C using the Rome III diagnostic criteria was similar to what has been reported previously for Japan [32, 33] or the other countries [34, 35]. Another limitation was that we did not investigate whether the presence of an organic GI disease and/or the other comorbid disease. It has been reported that IBS patients have more somatic/psychiatric comorbidities which may affect their daily lives compared to non-IBS subjects [36].

To summarize, a large population-based Internet survey has shown that a number of similarities between the Western countries and Japan, including a similar prevalence of IBS-C and a similar frequency of abdominal bloating in subjects with IBS-C. We have also shown important similarities with the previous surveys including a similar association of severity of abdominal pain with the degree of anxiety and a similar association of occurrence/exaggeration of IBS symptoms with meal ingestion and with perceived stress. Thus, these trigger factors are considered to be generalizable even in IBS-C. In constant, a significant association of frequency of bowel movement with the degree of anxiety has failed to be observed in IBS-C subjects.