Epidemiology of functional constipation and comparison with constipation-predominant irritable bowel syndrome: the Systematic Investigation of Gastrointestinal Diseases in China (SILC)

Authors


Prof. J. He, Department of Health Statistics, Second Military Medical University, 800 Xiangyin Road, Shanghai 200433, China.
E-mail: hejia63@yahoo.com

Abstract

Aliment Pharmacol Ther 2011; 34: 1020–1029

Summary

Background  The epidemiology and effects of functional constipation (FC) on Chinese people remain unclear.

Aim  To investigate the epidemiology of FC and its distinction from constipation-predominant irritable bowel syndrome (IBS-C) in China.

Methods  A cross-sectional survey was conducted in a representative adult Chinese population (= 16 078), which was selected from five regions using randomised, stratified, multistage sampling methodology. All respondents completed the modified Rome II questionnaire; 20% were asked to complete the 36-item Short Form (SF-36) and the Epworth Sleepiness Scale (ESS).

Results  Overall, 948 respondents (6%) had FC and FC was more prevalent in women than in men (8% vs. 4%, < 0.001). Straining and hard stools were the two most frequent symptoms. FC was associated significantly with dyspepsia and abdominal bloating. All SF-36 domain scores were lower for respondents with FC than for those without. The prevalence of clinically meaningful daytime sleepiness was significantly higher in respondents with FC than in those without (22% vs. 14%, = 0.003). Respondents with FC were more likely to strain, but less likely to have a feeling of incomplete emptying after a bowel movement than those with IBS-C. Respondents with IBS-C experienced similar demographics, quality of life and daytime sleepiness to those with FC.

Conclusions  The prevalence of FC in China is substantially lower than that in Western countries. FC has negative effects on quality of life and daytime sleepiness. The demographics and burden of illness are similar between FC and IBS-C, although the clinical symptoms are somewhat different.

Introduction

Constipation is a common, often chronic, disorder of gastrointestinal motility with a high prevalence; it affects up to 14–29% of adults in the Western population.1–3 The presence of constipation may affect patients’ quality of life, cause them to experience reduced productivity and increase the economic burden.4–6 The common view is that constipation can be self-treated with the large armamentarium of over-the-counter (OTC) treatment options. However, although most people with constipation have used such therapies, nearly half are not satisfied completely, mainly because of concerns regarding efficacy and safety.4 All these factors mean that constipation is a major public health issue.

The assessment of symptoms by structured interview or questionnaire is central to the diagnosis of constipation.1, 3, 4 Patients often experience constipation as a multisymptom disorder that includes infrequent bowel movements, hard or lumpy stools, straining, bloating, a feeling of incomplete evacuation after a bowel movement and abdominal discomfort.1 However, there is no widely accepted clinically useful definition of constipation. The Rome diagnostic criteria were developed as an appropriate standard to define constipation. In fact, constipation is a common symptom shared by patients with functional constipation (FC) and those with constipation-predominant irritable bowel syndrome (IBS-C). The primary factor that differentiates between these two diagnoses, according to Rome II, is the presence and prominence of abdominal pain or discomfort that is relieved on defecation in patients with IBS. It is thought that investigation of the differences between FC and IBS-C might provide further evidence to support the separation of the two disorders.7

To date, population-based studies on constipation have been carried out mainly in Western countries,3, 8, 9 and data from Asia are limited,10 especially in developing countries. Few population-based studies have estimated the prevalence of FC in China and the epidemiology of FC and its effects on Chinese people remain unclear. A study in Taiwan investigated the prevalence of FC and its effects;7 however, the subjects were not sampled randomly, which might have resulted in selection bias. Furthermore, there are no data on the comparative epidemiology of the subtypes of constipation in mainland China. Our study was conducted to investigate the epidemiology of FC, as defined by Rome II, and its effects, and to determine how FC is distinct from IBS-C in a large population sample of Chinese adults.

Materials and methods

Participants and study design

Randomised, stratified, multi-stage sampling methodology was used to select a representative sample of the general population from Shanghai, Beijing, Xi’an, Wuhan, and Guangzhou in China.11 By this approach, 3600 subjects aged 18–80 years were selected from each region (18 000 adults in total) after stratification by the overall age and sex distribution for that region. Rural and urban populations were sampled equally (= 1800 from each stratum in each region). Individuals were excluded if they were younger than 18 years, older than 80 years, illiterate, had major psychiatric illness, or had severe visual or hearing abnormalities or learning disabilities that might render them unable to complete the questionnaire. The design and methodology of the Systematic Investigation of Gastrointestinal Diseases in China (SILC) study are described in detail elsewhere.11

Survey instruments

Each individual selected was asked to complete: (i) a general information questionnaire, (ii) the Chinese version of the Reflux Disease Questionnaire (RDQ),11, 12 and (iii) the Chinese version of the modified Rome II questionnaire.13, 14 The general information questionnaire included information on age, height, weight, sex, education, total monthly family income, occupation, lifestyle habits (including smoking status, alcohol consumption and frequency of recreational exercise) and family history of gastrointestinal diseases. The RDQ was used to diagnose symptom-defined gastro-oesophageal reflux disease (GERD) and has been validated and described elsewhere.11

The validated Chinese version of the Rome II questionnaire was used to determine the presence of FC, IBS-C and other functional gastrointestinal disorders. The modified Rome II questionnaire used in our study included gastroduodenal, bowel and biliary items only.11 FC was defined in accordance with the Rome II criteria7 as the presence of two or more of the following six symptoms of constipation for at least 3 weeks, which need not be consecutive, in the past 3 months: (i) straining with more than 25% of the stool; (ii) lumpy or hard stools in >25% of defecations; (iii) sensation of incomplete evacuation in more than 25% of defections; (iv) sensation of anorectal obstruction/blockage in more than 25% of defections; (v) manual manoeuvres needed to facilitate >25% of defecations; (vi) fewer than three defecations per week.1, 7 IBS has been defined previously15 as abdominal discomfort or pain that had two of three features: (i) relieved with defecation; (ii) onset associated with a change in frequency of stool; (iii) onset associated with a change in form (appearance) of stool. IBS was described as IBS-C if patients had one or more of the following symptoms: (i) fewer than three bowel movements a week; (ii) hard or lumpy stools; (iii) straining during a bowel movement. Dyspepsia was defined, in accordance with Rome II, as persistent or recurrent pain or discomfort centred in the upper abdomen, with no evidence that symptoms were relieved exclusively by defecation or association with the onset of a change in stool frequency or stool form.15

In addition, a random subsample of 20% of the total sample from each region was asked to complete the Chinese version of the 36-item Short Form (SF-36)16 and the Epworth Sleepiness Scale (ESS).17 The SF-36, which measures health-related quality of life and the ESS, which quantifies daytime sleepiness, have been validated and described in detail previously.11

Data collection and response rate

A cross-sectional survey was conducted from April 2007 to January 2008. The questionnaires were self-administered, with trained and supervised facilitators available to explain any questions that respondents were unclear about. Respondents completed the questionnaires at home or in local residential committee offices. A total of 16 091 respondents completed the questionnaires with a response rate of 89%. Of the responses, 16 078 were suitable for analysis. The SF-36 and ESS questionnaires were completed by 3219 respondents (a response rate of 89%) and data from 3214 respondents were suitable for analysis. The demographics and lifestyle characteristics of the respondents have been described previously.11

Ethical considerations

The study was approved by the Ethics Committee of the Second Military Medical University, Shanghai, China. All participants gave their informed consent to participate in the study and were free to discontinue their participation at any time.

Statistical analysis

Odds ratios (ORs) and 95% confidence intervals (CIs) were calculated using multivariate logistic regression. The Cochran–Armitage test was used to detect trends. The chi-square test was used to compare the groups with FC and with IBS-C and the t-test was used to compare the SF-36 and ESS scores between individuals with and without FC or between individuals with FC and those with IBS-C. SAS 9.1.3 software (SAS Institute, Cary, NC, USA) was used for the data analyses. All of the above hypothesis tests were two-sided and a two-tailed P-value of 0.05 or less was considered to indicate statistical significance.

Results

Prevalence, demographics and lifestyle characteristics of respondents with Rome II-defined FC

Of the 16 078 respondents, a total of 948 participants (6%; 95% CI: 5.5–6.3%) were classified as having FC according to the Rome II criteria. The prevalence of FC increased in men among those aged 30-80 years (trend test: < 0.001) and in women among those aged 50-80 years (trend test: = 0.002). FC was more prevalent in women than in men (8% vs. 4%, < 0.001) throughout all age groups (Figure 1). The prevalence of FC in Shanghai, Beijing, Xi’an, Wuhan, and Guangzhou was 7%, 4%, 6%, 7% and 6%, respectively, and it varied significantly among the five study regions (< 0.001).

Figure 1.

 Age-and gender-specific prevalence of functional constipation (FC) based on a population sample of 16 078 respondents. *P < 0.05.

The demographic characteristics of respondents with and without FC and the associated potential risk factors are presented in Table 1. On multivariate analysis, FC was more common in women than in men (OR: 1.91; 95% CI: 1.57–2.32). Individuals aged 60–80 years were significantly more likely to have FC than those aged 30–39 years (60–69 years and 70–80 years vs. 30–39 years, OR: 1.79; 95% CI: 1.38–2.32 and OR: 2.62; 95% CI: 1.97–3.49, respectively). Participants with a family history of gastrointestinal disease were also more likely to report FC (OR: 1.74; 95% CI: 1.43–2.12). FC was associated negatively with occupation, body mass index (BMI) and frequency of recreational exercise (Table 1). No significant association was found between FC and living environment, education, family income, smoking status or alcohol consumption.

Table 1.   Characteristics of respondents with and without functional constipation (FC) and the associated potential risk factors
VariablesWith FC (= 948) n (%)Without FC (= 15 130) n (%)Multivariate OR* (95% CI)
  1. BMI, body mass index; OR, odds ratio; CI, confidence interval; GI, gastrointestinal.

  2. All data were generated from the general information questionnaire; numbers may not add up exactly where individual participants have refused to answer specific questions.

  3. * Adjusted for all variables in the table.

  4. † BMI ranges are appropriate for the Asian population (underweight: <18.5 kg/m2; normal: 18.5–22.9 kg/m2; overweight/obese: ≥23.0 kg/m2).

  5. ‡ Defined as alcohol consumed on at least four occasions per month.

Environment
 Urban475 (50)7597 (50)1.00
 Rural473 (50)7533 (50)1.07 (0.92–1.24)
Gender
 Woman655 (69)7735 (51)1.91 (1.57–2.32)
 Man293 (31)7395 (49)1.00
Age (years)
 18–29201 (21)3479 (23)1.02 (0.82–1.26)
 30–39182 (19)3493 (23)1.00
 40–49202 (21)3610 (24)1.15 (0.93–1.42)
 50–59139 (15)2329 (15)1.21 (0.96–1.54)
 60–69118 (12)1385 (9)1.79 (1.38–2.32)
 70–80106 (11)834 (6)2.62 (1.97–3.49)
BMI (kg/m2)†
 <18.5116 (12)1364 (9)1.00
 18.5–22.9476 (50)7245 (48)0.81 (0.65–1.01)
 ≥23.0352 (37)6457 (43)0.66 (0.52–0.83)
Education
 None/primary school239 (25)2943 (19)1.00
 Secondary/high school557 (59)9373 (62)1.01 (0.83–1.23)
 College graduate or beyond152 (16)2812 (19)0.78 (0.58–1.05)
Occupation
 Office worker262 (28)3950 (26)1.00
 Manual worker685 (72)11160 (74)0.80 (0.66–0.95)
Total monthly family income (yuan)
 ≤1999516 (54)8299 (55)1.00
 2000–4999367 (39)5596 (37)1.13 (0.97–1.31)
 ≥500065 (7)1194 (8)0.98 (0.73–1.30)
Smoking status
 Never smoker763 (81)10467 (69)1.00
 Current smoker153 (16)4278 (28)0.79 (0.63–1.01)
 Ex-smoker31 (3)383 (3)1.43 (0.95–2.15)
Alcohol consumption‡
 No821 (87)11992 (79)1.00
 Yes126 (13)3136 (21)0.99 (0.79–1.24)
Family history of GI disease
 No822 (87)13822 (91)1.00
 Yes126 (13)1301 (9)1.74 (1.43–2.12)
Frequency of recreational exercise
 Never152 (16)1979 (13)1.00
 Less than weekly80 (9)1283 (8)0.90 (0.68–1.20)
 At least weekly but less than daily143 (15)2051 (14)0.98 (0.77–1.24)
 Daily571 (60)9788 (65)0.75 (0.62–0.91)

Range of symptoms in respondents with FC

Respondents reported a wide range of symptoms and many reported more than one symptom. In the respondents with FC, the three most common symptoms were straining during a bowel movement (= 711, 75%), hard or lumpy stools (= 665, 70%) and fewer than three bowel movements a week (= 529, 56%). Figure 2 shows the overlap of these three symptoms. Other reported symptoms included a feeling of incomplete emptying after a bowel movement (31%), a sensation that the stool cannot be passed (46%) and a need to press on or around your bottom or vagina to try to remove the stool to complete the bowel movement (10%). A total of 431 respondents (46%; 95% CI: 42–49%) reported that they had only two of the above symptoms, whereas the remainder had at least three symptoms.

Figure 2.

 Overlap between the three most common symptoms (fewer than three bowel movements a week, hard or lumpy stools, straining during a bowel movement) reported by most respondents in the investigation (= 948).

Association with symptom-defined GERD and other functional gastrointestinal disorders

Symptom-defined GERD was more common in respondents with FC than in those without (6% vs. 3%; Table 2). However, the difference was not statistically significant (OR: 1.34; 95% CI: 0.97–1.84) after adjusting for age, gender, dyspepsia, aerophagia, functional abdominal bloating, and gall-bladder dysfunction. The presence of dyspepsia was associated significantly with an increase in the risk of FC (OR: 2.94; 95% CI: 2.17–3.99). A significant association was also found between FC and functional abdominal bloating (OR: 8.44; 95% CI: 6.98–10.20). There was no significant association between the presence of FC and aerophagia or gall-bladder dysfunction.

Table 2.   The association between functional constipation (FC), symptom-defined gastro-oesophageal reflux disease (GERD) and other functional gastrointestinal disorders
Functional disorder (n, %)Respondents with FC n (%)Respondents without FC n (%)Multivariate analysis OR (95% CI)*
  1. * Adjusted for age, gender and all variables in the table.

Symptom-defined GERD
 No (15582, 97)892 (94)14690 (97)1.00
 Yes (496, 3)56 (6)440 (3)1.34 (0.97–1.84)
Dyspepsia
 No (15691, 98)895 (94)14796 (98)1.00
 Yes (387, 2)53 (6)334 (2)2.94 (2.17–3.99)
Aerophagia
 No (15811, 98)914 (96)14897 (98)1.00
 Yes (267, 2)34 (4)233 (2)1.49 (1.00–2.23)
Functional abdominal bloating
 No (15435, 96)749 (79)14686 (97)1.00
 Yes (643, 4)199 (21)444 (3)8.44 (6.98–10.20)
Gall-bladder dysfunction
 No (16008, 99)941 (99)15067 (99)1.00
 Yes (70, 1)7 (1)63 (1)0.88 (0.38–2.08)

Burden of FC

Respondents with FC had significantly lower scores in all domains of the SF-36 than those without (all < 0.05) (Figure 3). The most substantial differences were observed in the role–physical, general health and role–emotional domains. For respondents with FC, there were no significant differences in SF-36 domain scores between men and women Respondents aged less than 40 years had significantly higher scores for physical functioning, role–physical and vitality domains than those aged 40 years or more and this difference was not found in other domains. With regard to the general health, vitality and mental health domains, the scores differed between respondents with fewer symptoms of constipation and those with three or more symptoms. However, there were no significant differences in other domain scores (data not shown).

Figure 3.

 Health-related quality of life in respondents with and without functional constipation. *P < 0.05.

Respondents with FC had slightly higher average scores on the ESS than those without {7.9 [standard deviation (s.d.) ± 5.7] vs. 6.8 ± 5.2, = 0.002}. The prevalence of clinically meaningful daytime sleepiness was significantly higher in respondents with FC than in those without (22% vs. 14%, = 0.003).

Comparison between respondents with FC and those with IBS-C

Of the total of respondents, 183 (1%) had IBS-C. Respondents with IBS-C were slightly younger on average than those with FC (41.9 ± 14.3 years vs. 45.5 ± 16.7 years, = 0.003). A family history of gastrointestinal disease was more common in respondents with IBS-C than in those with FC (20% vs. 13%, = 0.024). Respondents with IBS-C and those with FC had similar demographic characteristics with regard to environment, sex, BMI, education, occupation, total monthly family income, smoking status, alcohol consumption and frequency of recreational exercise (data not shown).

Table 3 shows the differences in various symptoms of constipation between respondents with FC and those with IBS-C. Respondents with FC were more likely to strain during a bowel movement than those with IBS-C (75% vs. 65%, = 0.005), whereas a feeling of incomplete emptying after a bowel movement was more frequent in respondents with IBS-C (38% vs. 31%, = 0.045). Other symptoms of constipation were similar in respondents with FC and those with IBS-C.

Table 3.   Differences in various symptoms of constipation between respondents with functional constipation (FC) and those with constipation-predominant irritable bowel syndrome (IBS-C)
Bowel disordersFC (= 948)IBS-C (= 183)P-value
Fewer than three bowel movements a week [n (%)]529 (56)104 (57)0.797
Hard or lumpy stools [n (%)]665 (70)119 (65)0.169
Straining during a bowel movement [n (%)]711 (75)119 (65)0.005
Feeling of incomplete emptying after a bowel movement [n (%)]291 (31)70 (38)0.045
A sensation that the stool cannot be passed [n (%)]437 (46)78 (43)0.388
A need to press on or around your bottom or vagina to try to remove stool to complete the bowel movement [n (%)]99 (10)18 (10)0.805

Of the 183 respondents with IBS-C, 26 (14%) had symptom-defined GERD. Respondents with FC were less likely to report GERD than those with IBS-C (OR: 0.47; 95% CI: 0.27–0.81). Dyspepsia was more prevalent in respondents with FC than in those with IBS-C (6% vs. 2%, = 0.032) and a significant association was found (OR: 3.62; 95% CI: 1.24–10.54). The prevalence of aerophagia was lower in respondents with FC than in those with IBS-C (4% vs. 13%, < 0.001) and a significant OR was observed (OR: 0.26; 95% CI: 0.14–0.48). Functional abdominal bloating was only found in respondents with FC. Other functional gastrointestinal diseases were similar in respondents with FC and with IBS-C (data not shown).

The comparison of health-related quality of life between respondents with FC and those with IBS-C is shown in Figure 4. Respondents with FC had higher scores than those with IBS-C in the mental health domain (= 0.001); however, no significant difference was found in the other SF-36 domains.

Figure 4.

 Health-related quality of life in respondents with functional constipation (FC) and those with constipation-predominant irritable bowel syndrome (IBS-C). *P = 0.001.

There was no significant difference in mean ESS scores between respondents with FC and those with IBS-C (7.9 ± 5.7 vs. 8.1 ± 4.9, = 0.821). The prevalence of clinically meaningful daytime sleepiness was also not significantly different between the two groups (19% vs. 22%, = 0.905).

Discussion

This was a large, population-based epidemiological study of FC that included a total population of 16 078 respondents from five regions in China. The overall prevalence of FC as defined by Rome II was 6%. The different definitions of constipation used in various studies have provided researchers with diverse prevalence rates. A population-based study in Canada reported that 27% of respondents self-reported constipation within the past 3 months and that 17% and 15% had FC according to the Rome I and Rome II criteria respectively.1 Another study showed that the prevalence of constipation was 30% for self-report, 19% for the Rome I criteria and 14% for the Rome II criteria in the same individuals.3 A systematic review stated that the mean reported rate of constipation in the general population of Europe was 17% and the median value was 17%.2 Another systematic review reported that the estimates of the prevalence of constipation in North America ranged from 12% to 19%.18 Compared with Western countries, previous studies have indicated a lower prevalence of FC in Asian countries and areas, such as Korea (9%), Taiwan (3–9%) and Singapore (12%).7, 10, 19, 20 The prevalence of FC in our study was also substantially lower than that in Western countries, although the prevalence varied among the five regions. The difference in the prevalence of FC among the regions may be due partially to the different dietary habits of the populations studied, which have been associated with constipation.21–23 The cultural and demographic variability in this vast country of China might also have caused the significant difference, as in other studies.7, 9 Studies on the causes of the regional differences are needed.

In this study from China, FC was more prevalent in women than in men, which is consistent with the observations from Western populations (2.2:1 woman-to-man ratio) and other Asian populations.1, 2, 24–28 Sex hormones might play a role in the predominance in women. In addition, it has been reported that women have delayed gastric emptying of liquids and solids compared with men.29

Consistent with most other studies,26 FC was more prevalent in older people than in younger individuals in our study. Significant risk factors for constipation in older women are failure of the anorectal angle to open or excessive perineal descent, which represent disturbances of pelvic floor function and rectal evacuation.30 However, other studies have reported that, for all definitions of constipation, the observed prevalence of FC was similar in different age groups.1, 3 Further systematic research is needed to clarify the basic mechanisms of neuromuscular dysfunction associated with ageing, including studies of the physical characteristics of the colonic wall, pelvic floor function and the neurohormonal control of motility and sensation.30

We found that FC was more common in office workers than in manual workers. This might because office workers experience a more sedentary lifestyle, whereas manual workers are involved in more frequent physical activities. Physical activity is a protective factor against constipation and respondents in our study who undertook daily recreational exercise had a lower prevalence of FC, which is consistent with the findings of other studies.3, 9 It has been reported that individuals of lower social, economic and educational levels have a tendency towards higher rate of constipation;2 however, we did not find an association between FC and educational levels or family income.

Some studies have reported that there is no significant relationship between BMI and FC;23, 31 however, we found that being overweight/obese was associated negatively with FC. It has been reported that BMI is correlated inversely with colonic transit time and that overweight/obese patients have more severe symptoms of urgency, loose stools and more stools per day.32 This might explain the association between BMI and FC in our study; however, further studies are needed. As with many other gastrointestinal conditions,15, 33 we found that FC had a significant relationship with a family history of gastrointestinal diseases. This might be due to common demographic risk factors as well as a genetic predisposition.34 Constitutional or hereditary characteristics are suggested by a high frequency of constipation among the relatives of patients.34 We found no association between FC and smoking status or alcohol consumption, which was consistent with the results of other studies.7

Our findings are consistent with previous reports in which patients with constipation reported a wide variety of symptoms.1 Straining during a bowel movement and hard or lumpy stools were the most frequent symptoms of FC, which was in line with the results of other studies.1, 7 The prevalence of a sensation that the stool cannot be passed and that of the need to press on or around your bottom or vagina to try to remove stool to complete the bowel movement was similar to that in Taiwan.7 However, the prevalence of a feeling of incomplete emptying after a bowel movement was only half that reported in Taiwan. The incidence of fewer than three bowel movements a week was higher in our study than in that from Taiwan.7

Some previous studies have identified a positive association between constipation and GERD;35, 36 however, this relationship was not confirmed in our study. It is possible that the attenuated significance of the results observed after adjustment for variables that are related to both FC and GERD, such as dyspepsia and functional abdominal bloating, might be explained by the fact that these risk factors are shared. Dyspepsia and functional abdominal bloating were associated significantly with FC, as reported in previous studies.4, 37 Although FC is often regarded simply as infrequency of bowel movements, it has been reported that it is actually a complex of multiple symptoms that varies in chronicity and intensity from one patient to another.4

According to the Rome II criteria, the primary difference in symptoms between FC and IBS-C is the presence of abdominal discomfort or pain in the latter. However, it has been argued that the criteria used to distinguish IBS from FC are arbitrary.38 In the current study, we found that the demographics of respondents with FC and those with IBS-C were similar, which was consistent with the results of the study from Taiwan.7 However, respondents with FC were more likely to strain during a bowel movement than those with IBS-C, whereas a feeling of incomplete emptying after a bowel movement was more frequent in respondents with IBS-C. Compared with respondents with IBS-C, GERD and aerophagia were less frequent in respondents with FC, but dyspepsia and functional abdominal bloating were more frequent.

The results of the study confirmed that FC has negative effects on quality of life and daytime sleepiness of respondents. It has been reported that respondents with FC have impaired physical and mental health and FC also has a significant negative effect on sleep quality.7, 39, 40 We have reported previously that IBS impairs the quality of life of respondents15 and similar results were obtained in the current study in respondents with IBS-C. Scores on the SF-36 were similar between respondents with FC and those with IBS-C in most of the domains, as were the scores on the ESS. This implies that FC and IBS-C had similar effects on the respondents.

The main strength of this study is that it was a large, truly population-based study of the epidemiology of FC in China that used validated questionnaires and also involved a comparison with IBS-C. The study provides important and generalisable data on the epidemiology of FC and has the potentials to make a major contribution to the epidemiological understanding of FC and IBS-C in China. However, the study has some potential limitations. Given that a cross-sectional design was used, the study does not enable the directionality of relationships between FC and IBS-C to be assessed. Another limitation is the lack of information about the current medications used by respondents. In addition, patients with organic causes of constipation were not excluded.

In conclusion, the prevalence of FC in China as determined by this large population-based study was substantially lower than that in Western countries. FC was associated with a significant burden of illness. The demographics, health-related quality of life and the prevalence of clinically meaningful daytime sleepiness were mostly similar between FC and IBS-C, although the clinical syndromes are somewhat different.

Acknowledgements

Declaration of personal interests: None. Declaration of funding interests: The study was funded by AstraZeneca R&D, Mölndal, Sweden. AstraZeneca had no role to play in the content and conduct of the study. Professor Jia He had full access to all of the data in the study and took responsibility for the integrity of the data and the accuracy of the data analysis.

Ancillary