Review for 10.1186/s12876-024-03543-x (2025)

Title: Daily Sodium Intake and Constipation in US Adult Males: An Uncommon Negative
Association Revealed by National Health and Nutrition Examination Survey Data from the
United States (2005–2010)
Version: 0 Date: 01 Oct 2024
Reviewer:  Hanieh Malmir
Reviewer's report:
Dear Authors,
I have carefully reviewed your manuscript, "Daily Sodium Intake and Constipation in Adult
Males: An Uncommon Negative Association Revealed by NHANES Data (2005–2010)," and
commend your thorough use of NHANES data to explore this novel association. However, I
believe several methodological and scientific issues require further consideration to strengthen
the study. Below are my suggestions:
Cross-sectional design and causality:
While the manuscript acknowledges that NHANES data are cross-sectional, the current
discussion may still lead to misinterpretation of the results as causal. I recommend emphasizing
that your findings show only an association and not a causal relationship between sodium intake
and constipation. It might be helpful to propose future longitudinal or interventional studies to
explore causality.
Sodium intake and constipation measurements:
Sodium intake is assessed via self-reported 24-hour dietary recall, possibly introducing recall
bias. Additionally, the two-day sodium intake might not adequately reflect habitual intake.
Addressing the limitations of this method in the manuscript will strengthen its transparency.
Self-reported stool consistency (Bristol Stool Form Scale) and defecation frequency are also
subjective. Consider discussing the potential for measurement bias and exploring ways to
mitigate this in future research.
Confounding and multicollinearity:
Despite adjusting for several covariates, residual confounding (e.g., fluid intake, medication use,
or other gastrointestinal disorders) might still be present. It would be helpful to acknowledge
the possibility of unmeasured confounders in the manuscript.
Some covariates, such as dietary fiber and fluid intake, may be highly correlated with sodium
intake. Addressing potential multicollinearity in your regression models or clarifying whether
this was assessed would improve the study's methodological rigor.
Multiple comparisons in subgroup analyses:
The manuscript conducts numerous subgroup analyses without adjusting for the increased risk of
Type I errors. Applying a correction (e.g., Bonferroni) would reduce the chance of false positives
and enhance the reliability of your results.
Discussion of contradictory findings:
The current literature shows mixed results regarding the association between sodium intake and
constipation. Providing a more in-depth comparison with studies showing positive associations
and discussing population-specific dietary habits (e.g., differences in sodium sources) would
provide a clearer context for your findings.
Physiological mechanisms:
While the discussion proposes potential mechanisms (e.g., hydration regulation, gut motility),
these are speculative and not directly tested in the study. Emphasizing the need for future
mechanistic studies to verify these hypotheses will balance the interpretation of your results.
Generalizability:
The exclusive focus on adult males limits the generalizability of your findings to females and
other populations. Consider discussing the implications of this limitation and how future studies
could explore similar associations in other groups.
Statistical analysis:
You used Restricted Cubic Spline (RCS) methods to explore non-linear trends. While this
approach is appropriate, it would be helpful to provide more justification for its use and consider
alternative approaches to detect non-linearity.
Addressing these points will improve the robustness and clarity of your study. I believe your
research contributes valuable insights into an underexplored area, and refining these aspects will
enhance its impact.
Best regards,