Dear editor
We read with interest the article by Huang et al, which used NHANES 2007–2020 data to examine the association between daily sitting time and urinary leakage and then explored whether DII, BMI, NLR, and leisure-time physical activity might help account for that association1 The study is likely to draw attention because it brings sedentary behavior, inflammatory correlates, and urinary symptoms into the same analytic framework. The reported association between longer sitting time and higher odds of urinary leakage is also relevant to readers in urogynecology and epidemiology.1 Our concern is narrower: some parts of the abstract, discussion, and conclusion seem to encourage a mechanistic interpretation that is stronger than the design can support.
That distinction matters because mediation analysis is most informative when the ordering of exposure, mediator, and outcome is credible and the assumptions behind the model are made explicit.2,3 Huang et al do acknowledge that the cross-sectional design limits temporality and causality and that the mediation analyses should be interpreted as statistical associations rather than confirmed causal pathways1 Even so, the paper still refers to inflammatory mechanisms through which prolonged sitting may increase urinary leakage and to LTPA as a factor that may mitigate that risk.1 A more cautious reading may be that the observed pattern is consistent with an inflammatory or behavioral pathway, while still falling short of establishing that pathway.
A related issue is the role assigned to BMI, DII, and NLR across analyses. In the fully adjusted logistic model, these variables were entered as covariates; later, they were examined as mediators.1 That does not invalidate the analyses, but it does make the target estimand harder to read. Adjustment for variables that may lie on the pathway can complicate interpretation and blur the distinction between a confounder-controlled association and a pathway analysis.4,5 A prespecified causal diagram and formal sensitivity analyses for mediation assumptions were not reported,1 which leaves some uncertainty about how the reported direct and indirect effects should be understood.
The baseline pattern for DII points in the same direction. In Table 1, longer sitting time was associated with lower DII values and a higher proportion of participants classified as having an anti-inflammatory diet, while the group with the longest sitting time also had higher educational attainment.1 That pattern is worth pausing over. NHANES-based work has shown that DII varies by education and income,6 and the index itself was developed to characterize the inflammatory potential of diet rather than to function as a direct inflammatory biomarker.7 Socioeconomic position may therefore be shaping the observed DII gradient, but stratified analyses or interaction testing for that explanation were not reported.1 As presented, the data may fit more than one account: mediation, socioeconomic confounding, or some combination of the two.
None of this weakens the main observation that greater sitting time and urinary leakage were associated in this sample, a finding that is broadly in line with earlier NHANES-based analyses.8,9 Our suggestion is simply that the conclusions would be easier to interpret if the mediation results were framed as association-based, if the rationale for treating BMI, DII, and NLR as both covariates and mediators were made explicit, and if the DII findings were explored in relation to socioeconomic position. Those clarifications would help readers judge more clearly what this study shows now and what still requires prospective data.
Funding Statement
The authors received no specific funding for this communication.
Artificial Intelligence (AI) Use Disclosure
Generative AI tools were used solely for language refinement and formatting assistance. All scientific interpretation, critique, and scholarly content were independently developed by the authors.
Data Sharing Statement
No new data were generated or analysed in this communication.
Disclosure
The authors declare that they have no competing interests in this communication.
References
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Data Availability Statement
No new data were generated or analysed in this communication.