Review for 10.1186/s12876-024-03373-x (2024)

Title: Overweight and vitamin D deficiency are common in patients with irritable bowel
syndrome. A cross-sectional study
Version: 1 Date: 31 Mar 2024
Reviewer's report:
1. The type of study design should be specified in the study title.
2. "Background; " - Please use colon (:) instead of semicolon.
3. "The etiology of irritable bowel syndrome (IBS) is unknown, but female sex, dietary
habits, and psychological factors have been discussed as risk factors for the disease [1]. "
- More accurately, numerous pathogenic factors have been proposed, including alterations
in gastrointestinal motility, visceral hypersensitivity, gut-brain axis dysfunction, low-grade
(chronic) intestinal inflammation and impaired epithelial barrier integrity, etc. (citation:
pubmed.ncbi.nlm.nih.gov/37110143). This should be mentioned.
4. "Poor food habits for several years may lead to cognitive failure ..." - What is 'cognitive
failure'??
5.  How was the sample size determined? The control group (n=50) is substantially smaller than
the IBS group (n=260), which might be underpowered and not provide an adequate comparison
base. In particular, the analyses of subgroups based on IBS type are seriously limited by smaller
sample sizes within each subgroup.
6.  It is unclear why the study investigators chose to recruit the healthy controls from hospital
staff and students, which could introduce bias, as these populations might not be representative
of the general population in terms of health behaviors, access to healthcare, and socioeconomic
status, etc. At least some explanation should be provided.
7. "Questions No 40–48 in the Swedish version of the questionnaire was used, after having
received license from The Rome Foundation, Inc. Raleigh, NC, USA." - An accompanying
citation should be provided here.
8. Please change "The IBS patients were elder than controls " to "The patients with IBS were
older than the controls ( ___ vs ____, p=_____)".
9. Given that the IBS cases were younger than controls, which could influence outcomes since
age and gender can affect both IBS prevalence and vitamin D levels, the adjustment for age in
statistical analyses is noted but there is no clear mention of adjusting for gender distribution or
ensuring comparable groups in terms of these demographics.
10. For a study investigating nutritional deficiencies, there is minimal detail on dietary
assessment beyond dietary supplements. Incorporating comprehensive dietary assessments,
including dietary patterns and specific intake of vitamin D-rich foods, would provide a clearer
picture of the nutritional status and its relationship with IBS. There is a lack of detailed
assessment of dietary intake, which is crucial given that the study aims to explore nutritional
deficiencies. Please rectify this.
11. With multiple outcomes assessed (weight, BMI, micronutrient levels, symptom scores)
in this study, it is unclear if the authors adjusted for multiple comparisons e.g. Bonferroni
correction, which is necessary to mitigate the risk of increased type I error (i.e. false positives).
Please clarify.
12. In the discussion section it is worth mentioning that vitamin D supplementation might
also improve IBS symptoms and QoL among sufferers as per a recent meta-analysis (citation:
pubmed.ncbi.nlm.nih.gov/35396764).
13. The discussion of study limitations was incomplete. What about the  potential for dietary
recall bias and the limitations of self-reported data for dietary intake and symptom severity?