Constipation is a common symptom across the world, affecting multiple aspects of a person’s health and their quality of life. The prevalence of constipation varies according to the diagnostic criteria used, but estimates put its prevalence between 2.6% and 26.9% (1). The Rome diagnostic criteria are the most commonly accepted standard, recognizing constipation as a subset of functional bowel disorders (2). The main clinical manifestations include difficulty in defecation, low defecation volume, decreased defecation frequency or incomplete defecation, and related discomfort. Constipation is a complicated condition and its pathogenesis is multifactorial (2, 3). There are various factors that are associated with constipation. The most frequently cited associated risk factors for constipation are female gender and advanced age (1, 3–5).

For patients with constipation as the only indication (i.e., without “high-risk symptoms” such as rectal bleeding, weight loss, and iron deficiency anemia), the guidelines do not explicitly recommend colonoscopy (6–8). In recent years, a considerable number of studies have addressed colonoscopy for patients with constipation as the sole clinical feature to investigate the association of constipation with colorectal cancer (CRC), colorectal polyps, and other significant pathological findings. A significant association between colorectal cancer and constipation has been observed (9–11), while other studies have shown the prevalence of neoplastic lesions to be low (12, 13). However, these recent studies were limited to colonoscopy diagnostic results, ignoring the analysis of relationships between other elements of the colonoscopy procedure and constipation. Data on the characteristics of intestinal morphologies associated with constipation are scarce.

The focus of this investigation was to summarize and analyze intestinal morphologies in constipation patients who underwent anesthetized colonoscopy. A subgroup analysis was conducted on common risk factors, such as female gender and advanced age, to provide further exploration for the study. The study posed the following question: “Do the characteristics of intestinal morphologies as determined by colonoscopy affect constipation or not?”

Between March 2020 and February 2021, we enrolled 510 patients (260 in the constipation group and 250 in the control group) into the study. Comparisons of the variables in the propensity model between the two groups of patients are summarized in Table 1 . There were statistically significant differences between the two groups in terms of gender (p < 0.001), age (p = 0.002), and operation time (p < 0.001), but not for any other factors. In addition, the diagnosis of enteritis showed a tendency toward a statistically significant difference between groups, but did not reach significance (p = 0.066).

A comparison of the characteristics of intestinal morphologies determined by colonoscopy is shown in Table 2 . There were meaningful differences between cohorts for the intestinal morphologies of tortuousness (p < 0.001) and dissociation (p < 0.001). Meanwhile, a significant difference between cohorts was observed for either a combination of tortuousness and dissociation (p < 0.001) or tortuousness alone without other conditions (p = 0.015) However, no significant difference between groups was observed for dissociation without any other conditions (p = 0.007).

Referring to the World Health Organization (WHO) 2020 age classification standards, the participants were divided into three age groups: 18–44 years old (young), 45–59 years old (middle-aged), and over 60 years old (elderly). Furthermore, based on median operation time, the participants were divided into those with an operation time less than or equal to 12 minutes, and those with an operation time greater than 12 minutes. Subgroup analysis was conducted for statistically significant variables—gender, age, and operation time—and the results showed that regardless of the subgroup analysis, there was a statistically significant difference in tortuousness (all p-values < 0.05) between groups. In addition, there was a statically significant difference in dissociation for men (p < 0.001), elderly people (p < 0.001), and those with a longer operation time (p = 0.001). The subgroup/sensitivity analysis for the characteristics of intestinal morphologies determined by colonoscopy is shown in Table 3 .

In this study, we found that people with the intestinal morphologies of tortuousness and dissociation seem to more often experience constipation, especially those with tortuousness, than the general population. Moreover, further analysis using subgroups did not attenuate this relationship.

The association of constipation with colonoscopy diagnostic results for diseases such as CRC has been an area of particular interest in the constipation field in recent years (17, 18). However, little is known about the relationship between constipation and other elements of the colonoscopy procedure, especially the characteristics of intestinal morphologies. This is, to our knowledge, the first study to present data from a Chinese hospital on the association of constipation and characteristics of intestinal morphologies. In this report, we evaluated this association in 510 patients and further explored it by using subgroups in order to provide a valuable reference of the characteristics of intestinal morphologies and their effect on constipation.

Multiple factors typically converge in the pathology of constipation, including intrinsic factors, behavioral factors, and environmental factors (19, 20). A review of the literature on studies conducted in North America suggests that the prevalence of constipation is consistently higher in women than in men and increases gradually with age, particularly after the age of 70 years (21). A possible contributing factor to the higher rates in females may be higher risk of injury to the pelvic floor muscles and nerves that are required for defecation (22) following childbirth (23). In addition, most epidemiologic studies demonstrated a higher prevalence of constipation in elderly individuals (1, 5, 24), due in part to intrinsic changes in colonic motility and physiology in the elderly, such as an increase in collagen deposition in the left colon (25), which predisposes individuals to developing constipation (24).

Moreover, gastrointestinal disorders such as enteritis may play a part in the onset of constipation (26). Parthasarathy et al. (2016) found that mucosal microbiota might affect epithelial and mucosal function, and achieved 94% accuracy for discriminating between healthy individuals and constipated individuals by examination of fecal and colonic mucosal microbiota (27). In addition, the quality of colon cleansing directly affects the ability of the clinician to perform a high-quality examination because of difficulty in visualizing mucosa, which affects the diagnostic yield (28). Thus, the BBPS and colonoscopy diagnosis were included in the adjusted model.

Furthermore, the prevalence of constipation varies between countries even when uniform criteria are used. Consequently, environmental, cultural, ethnic, dietary, or genetic factors may influence the incidence of constipation (29). In this study, almost all patients came from Zhongshan, Guangdong Province, China, which minimized the geographical variability. In our opinion, such conditions also minimized the effect of the association between geographical factors and constipation. Consequently, we did not incorporate geographical factors into our model. This might cause some interference with the results and is a shortcoming of the study.

Defecography is one of the most common examinations performed on constipated patients. This examination can show the shape of the anorectal and partial colon region, but generally fails to fully reflect the complete state of the colon. A colonoscopy serves as a common endoscopic examination and intervention procedure (30), and it can provide the possibility for novel observations. Abnormalities of intestinal morphologies may be causal agents that hinder or delay fecal emptying, thereby contributing to constipation, but the association of the characteristics of intestinal morphologies as determined by colonoscopy and their link to constipation is not well studied. To this end, we designed the study to answer the question: “Do the characteristics of intestinal morphologies as determined by colonoscopy affect constipation or not?” Some preliminary conclusions were drawn, but verification by other studies is still needed.

There were several limitations to this study. Owing to the limitations of its design, the other risk factors for constipation, such as sport activity and low fluid intake, were absent from the data collection. The selection of variables was underrepresented, resulting in limitations for the model. In addition, the sample size may have been insufficient, which could have deviation in the statistical analysis. A larger sample size and multicenter study is needed for further research and evaluation. In addition, the majority of the enrolled patients in the constipation group were female; although this is consistent with the epidemiology of constipation and normal in general population studies of constipation, it may have impacted the generalization of the characteristics of intestinal morphologies for men with constipation. Despite these limitations, we hope that our results can be informative for the selection of treatment methods for constipation.

This study showed that compared with the general population, people with intestinal morphologies of dissociation and especially tortuousness seem to more often experience constipation. Our study provides accumulated data on constipation, and we believe that our results are a valuable resource for the study of constipation.

The raw data supporting the conclusions of this article will be made available by the authors, without undue reservation.

The studies involving humans were approved by the Institutional Review Board (the local Ethics Committee of the hospital) and the registration number for this study was 2019ZSZY-LLK-039. The studies were conducted in accordance with the local legislation and institutional requirements. The participants provided their written informed consent to participate in this study.

YX: Writing—original draft. QX: Writing—review and editing.