Reviewer’ s report
Title: Relationship of Breastfeeding Duration with Joint Pain and Knee Osteoarthritis in Middle-
aged Korean Women: A Cross-sectional Study using the Korea National Health and NutritionExamination Survey
Version: 0Date: 02 Jun 2020
Reviewer's report:
Thank you for the opportunity to review this paper, which describes a cross-sectional analysis of
data from the KNHANES dataset to investigate the relationship between breastfeeding durationand joint pain and knee osteoarthritis (OA) in Korean women. Overall, the paper is clearly writtenand easy to follow, but can be improved according to my suggestions below.
Abstract
-the authors need to emphasise that it is 'prior' breastfeeding and 'current' joint pain and knee OAthat is being assessed in the study-the last two sentences of the Methods section would be better placed at the start of the Resultssection-the 'reanalysis' is better referred to as a 'sensitivity analysis' (here and in the main Methods)-Conclusion: no mention is made previously regarding menopause in the Results section, and thissentence refers to 'elderly women' rather than 'middle-aged women' as referred to in theBackground section
Background
-are there any available data on the prevalence of breastfeeding specifically in Korea, to provide
context for this study?
-the effect of joint health on quality of life needs to be described in more detail here-how is 'long-term breastfeeding' defined? Is this for one child, or in total ie for multiple childrenthat were breastfed by the same mother?
Methods
-please include a statement about the study design, eg secondary analysis of cross-sectional data-technically it's the 'odds' of joint pain rather than the 'risk' of joint pain that was examined with thelogistic regression analysis-it's not clear why there is a difference in KNHANES numbers for 'number of subjects' and 'actualnumbers of participants'-breastfeeding duration: please clarify how this question was asked in KNHANES - is it for thetotal breastfeeding duration for a mother (ie across multiple children)? I'm presuming this is thecase given that some women breastfed for >4 years. And what if mothers had multiple births egtwins who were both breastfed - does this count for double the breastfeeding time?-it's not clear how physical activities were classified into moderate versus intense activities-'non-breastfeeding group as the standard baseline' should be reworded to reflect that this groupwas used as the 'reference' or 'reference group'
-the terms 'prevalence' and 'incidence' seem to be used interchangeably throughout the paper but
have different epidemiological meanings; I think that 'prevalence' is probably more appropriate forthis study-were hip radiographs also performed for the KNHANES?-for the statement "In the overall analysis, "joint pain" was defined as the case where there wasmore than one joint pain in three sites" but shouldn't anyone who had at least one joint pain beclassified as a 'joint pain case' for the analysis?
Results
-relatively few women (only 8% of the sample) were classified as 'non-breastfeeding'; how might
this have impacted on your analysis?-it would be best to have a new subheading for the sensitivity analysis looking at the ≥60 years age
group-Table 2: the second breastfeeding category refers to 'breastfeed ≥1 month' - does this mean that
any women who breastfeed for less than 1 month were classified as 'non-breastfeeding'? Thisneeds to be clarified and stated in the Methods-in the reporting of the results (both in the Abstract and the main Results section) it would bepreferable to report 95%CIs for the odds ratios, rather than p-values; also it would be best to statewhether the reported odds ratios are 'unadjusted odds ratios' or 'adjusted odds ratios'.
Discussion
-first paragraph: as mentioned earlier, it would be best to state that it is 'prior' breastfeeding and'current' joint pain and knee OA that has been examined in this study-the breastfeeding question is likely to be impacted by recall bias - it's likely difficult to rememberthe exact duration from decades previously; the authors have alluded to this in the Discussion butwould be good to refer specifically to the possibility of 'recall bias' here
-is it possible that there may be some negative stigma associated with not breastfeeding as this was
the cultural norm back in the 1960s-70s? So perhaps women who did not breastfeed might haveincorrectly responded that they did breastfeed?-second paragraph: better to refer to 'greater odds ratios' rather than 'more significant correlations'as it's the magnitude of association that's important rather than the statistical significance of these-the statement 'the study was conducted among a large-scale group representative of Korea' needsto be supported by references, and explained how it is representative (ie in terms of average age,gender, socioeconomic distribution)-the paragraph on hormonal changes after birth and during breastfeeding needs to be linked betterto why these changes might affect joint health-with a decline in breastfeeding rates over time, does this mean that future generations of Koreanwomen can be expected to have lower rates of OA? Perhaps can add this in to the Discussion as anavenue for future research-the paragraph on residence/sedentary behaviour does not add much to the Discussion and Irecommend removing this-I don't consider that the 'accuracy of analysis was increased', as the authors suggest, by looking atself-reported and radiographic outcomes - instead the authors could state that they have taken acomprehensive approach to examining joint health outcomes that reflects contemporary methods
for the clinical diagnosis of OA
Conclusion
-'risk of exposure to disease' should be reworded to read 'the odds of joint pain and/or knee OA',reflecting the logistic regression analyses that were undertaken-second paragraph: this would be better placed in the main Discussion rather than in theConclusion, as it has implications for practice and policy
Are the methods appropriate and well described?
If not, please specify what is required in your comments to the authors.
NoDoes the work include the necessary controls?
If not, please specify which controls are required in your comments to the authors.
YesAre the conclusions drawn adequately supported by the data shown?
If not, please explain in your comments to the authors.
YesAre you able to assess any statistics in the manuscript or would you recommend an
additional statistical review?If an additional statistical review is recommended, please specify what aspects require further
assessment in your comments to the editors.
I am able to assess the statisticsQuality of written English
Please indicate the quality of language in the manuscript:
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