Bodyweight change and cognitive performance in the older population

Judith M. Kronschnabl; Thorsten Kneip; Luzia M. Weiss; Michael Bergmann

doi:10.1371/journal.pone.0249651

Peer Review History

Original SubmissionDecember 7, 2020
22 Jan 2021 Decision Letter - David Meyre, Editor PONE-D-20-38422 Bodyweight change and cognitive performance in the older population PLOS ONE Dear Dr. Kronschnabl, Thank you for submitting your manuscript to PLOS ONE. After careful consideration, we feel that it has merit but does not fully meet PLOS ONE’s publication criteria as it currently stands. Therefore, we invite you to submit a revised version of the manuscript that addresses the points raised during the review process. Please submit your revised manuscript by Mar 07 2021 11:59PM. If you will need more time than this to complete your revisions, please reply to this message or contact the journal office at plosone@plos.org. When you're ready to submit your revision, log on to https://www.editorialmanager.com/pone/ and select the 'Submissions Needing Revision' folder to locate your manuscript file. 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Please see our Supporting Information guidelines for more information: http://journals.plos.org/plosone/s/supporting-information. [Note: HTML markup is below. Please do not edit.] Reviewers' comments: Reviewer's Responses to Questions Comments to the Author 1. Is the manuscript technically sound, and do the data support the conclusions? The manuscript must describe a technically sound piece of scientific research with data that supports the conclusions. Experiments must have been conducted rigorously, with appropriate controls, replication, and sample sizes. The conclusions must be drawn appropriately based on the data presented. Reviewer #1: Yes Reviewer #2: Yes ******** 2. Has the statistical analysis been performed appropriately and rigorously? Reviewer #1: Yes Reviewer #2: Yes ****** 3. Have the authors made all data underlying the findings in their manuscript fully available? 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Any typographical or grammatical errors should be corrected at revision, so please note any specific errors here. Reviewer #1: Yes Reviewer #2: Yes ****** 5. Review Comments to the Author Please use the space provided to explain your answers to the questions above. You may also include additional comments for the author, including concerns about dual publication, research ethics, or publication ethics. (Please upload your review as an attachment if it exceeds 20,000 characters) Reviewer #1: This is an interesting paper examining the association between body weight change and cognitive performance. The methodology is impressive with good sample size. The analysis is careful and I agree that the paper is promising and may contribute to the literature. Comments: 1. When discussing about obesity paradox, it is important to acknowledge and account for the limitation of using BMI as the only measure of obesity. Previous studies have showed that waist circumference and waist-to-hip predicted cognitive performance better than BMI. I understand that the authors used grip strength, but I am not clear how this can address the limitation of the lack of waist circumference measure. More elaboration is necessary and this limitation should be noted in the discussion. 2. Another limitation that should be acknowledged and discussed is the cognitive measures employed in the current study. Only a short immediate and delayed recall tasks were used. The authors should discussed the validity of these tasks in measuring cognitive functions. How reliable is the tasks? Some previous studies have found that the link between obesity cognitive functions may depend on the tasks and the specific cognitive abilities that were measured. More discussion is necessary and possible limitations should be acknowledged appropriately. Reviewer #2: The manuscript shows an interesting human study, which could have potentially significant implications in the field of understanding the relationship between BMI and cognition. The study as presented shows that, weight gain is, on average, not significantly related to cognitive performance, concluding that the association between weight change and cognitive performance in older age is based on weight changes being related to illness and recovery. However, there are some concerns related with this work: Major revision: The selected participant average age is 66,94 years. As commented by the authors based on a review of the literature, Smith et al. have suggested that the mean age of the study sample may be a crucial factor with a positive weight-cognition association only emerging in samples with mean age above 72 years. However the chosen age to perform the study is an age that is closer from the adulthood rather than elderly. Therefore, the study should be completed adding another group above 72 years, as suggested by the literature. Minor revision: Figure legends are missing. ****** 6. PLOS authors have the option to publish the peer review history of their article (what does this mean?). If published, this will include your full peer review and any attached files. If you choose “no”, your identity will remain anonymous but your review may still be made public. Do you want your identity to be public for this peer review?** For information about this choice, including consent withdrawal, please see our Privacy Policy. Reviewer #1: No Reviewer #2: No [NOTE: If reviewer comments were submitted as an attachment file, they will be attached to this email and accessible via the submission site. Please log into your account, locate the manuscript record, and check for the action link "View Attachments". If this link does not appear, there are no attachment files.] While revising your submission, please upload your figure files to the Preflight Analysis and Conversion Engine (PACE) digital diagnostic tool, https://pacev2.apexcovantage.com/. PACE helps ensure that figures meet PLOS requirements. To use PACE, you must first register as a user. Registration is free. Then, login and navigate to the UPLOAD tab, where you will find detailed instructions on how to use the tool. If you encounter any issues or have any questions when using PACE, please email PLOS at figures@plos.org. Please note that Supporting Information files do not need this step. https://doi.org/10.1371/journal.pone.0249651.r001
Revision 1
19 Mar 2021 Author Response Dear reviewers, thank you very much for your valuable comments and the opportunity to revise our manuscript. We carefully addressed your comments and believe that our paper has been considerably improved by this. Please find below our detailed answers to the points you have raised as well as an additional note on the changes applied to the manuscript during the course of revising the manuscript. The page numbers in our answers refer to the revised manuscript. Response to reviewers Reviewer #1: 1. "When discussing about obesity paradox, it is important to acknowledge and account for the limitation of using BMI as the only measure of obesity. Previous studies have showed that waist circumference and waist-to-hip predicted cognitive performance better than BMI." We fully agree that BMI or any other weight-based measure alone is an insufficient measure. In fact, we tried to argue that it is necessary to complement it with a measure that allows for a differentiation between lean muscle mass and fat mass, where waist circumference or waist-to-hip ratio would be examples for measures of the latter (p.6). "I understand that the authors used grip strength, but I am not clear how this can address the limitation of the lack of waist circumference measure. More elaboration is necessary and this limitation should be noted in the discussion." We used grip strength, which has been demonstrated to be correlated with lean muscle mass (see added references in the manuscript), particularly intra-personally as we employ it as a proxy for muscle mass. If it were a (close to) perfect measure, this would capture any possible effect related to lean muscle mass, while BMI would capture the residual effect related to fat mass. We tried to make this clearer in the revised manuscript (p.6) and added references that back up our interpretation (p.10). However, we have to acknowledge that grip strength is probably not a perfect proxy. If waist circumference or waist-to-hip-ratio had been available in the data, we could have used one of them as complement instead. If we had done so, the residual effect of BMI would have to be interpreted as an effect of (changes in) lean muscle mass. Unfortunately, we are restricted to grip strength. On a conceptual level, it is still supposed to capture muscle mass, on the operational level, it may be suboptimal. We acknowledge and discuss this limitation in an additional paragraph added to the discussion (see 3rd paragraph in the discussion, p.25f). 2. "Another limitation that should be acknowledged and discussed is the cognitive measures employed in the current study. Only a short immediate and delayed recall tasks were used. The authors should discussed the validity of these tasks in measuring cognitive functions. How reliable is the tasks? Some previous studies have found that the link between obesity cognitive functions may depend on the tasks and the specific cognitive abilities that were measured. More discussion is necessary and possible limitations should be acknowledged appropriately." Indeed, we only use a single combined measure for memory and recall to measure cognition and we agree that this fact deserves a more thorough discussion of implications and possible limitations. To address the raised concern, we therefore extended the paragraph on the used cognition measure and put it in the context of the different proclaimed domains of cognitive functioning (p.9). We also provide some arguments in favour of its use: It is based on an established and validated test that was found to be affected earlier and stronger by ageing than crystallised cognitive skills, such as numerical or verbal abilities. In addition, it has some desirable properties (from a statistical point of view), which warrant its use. While we think the focus on memory/recall is justifiable, it is true that our results do not readily generalize to other domains of cognitive functioning. We acknowledge and discuss this limitation in an additional paragraph added to the discussion (see 4th paragraph in the discussion, p.26). We still believe in the importance of our contribution for this field of research – carefully scrutinizing possible mechanisms (including methodological pitfalls) that might contribute to the association of interest. We would highly appreciate if our study stimulates further research considering other domains of cognitive functioning. Reviewer #2: Major revision: "The selected participant average age is 66.94 years. As commented by the authors based on a review of the literature, Smith et al. have suggested that the mean age of the study sample may be a crucial factor with a positive weight-cognition association only emerging in samples with mean age above 72 years. However, the chosen age to perform the study is an age that is closer from the adulthood rather than elderly. Therefore, the study should be completed adding another group above 72 years, as suggested by the literature." This is an excellent comment. We had indeed considered splitting our sample into young-old and older-old and had already looked at respective models in earlier versions of our manuscript. We opted against going deeper into this in order not to overburden the manuscript and given that we systematically address effect heterogeneity by age. On second thought, your suggestion offers a more straightforward link to the previous literature. However, since this literature is essentially cross-sectional, we felt it required drawing some more attention to the cross sectional models to first check whether we can replicate the finding of a (more) positive association in our data. For this reason, we decided to introduce basic control variables already at an earlier stage (i.e. into the POLS models) to be more comparable. We finally addressed your comment by splitting our sample into two age groups: one group, where respondents entered the panel at 65 years or above and another group for younger respondents. We chose this cut-point because it is close of the inflection point in the inversely u-shaped age profiles for both BMI and cognition in our data and subsample sizes are not overly unbalanced. Moreover, mean age in the older subsample is reasonably high with about 76 years on average (60 years for the younger). We then replicated our analyses separately for both sample splits and added two new paragraphs (p.21; p.22), where we summarize and discuss results in the manuscript. Full details, including test statistics for differences in coefficients across subsamples, are provided in the supplementary material. In short, we found cross-sectional associations to be significantly higher (although not significantly positive) in the older sample. In the panel analyses, both weight gain and weight loss effects were more pronounced in the older sample, but differences were not significant; neither were the weight gain effects themselves. The recovery effect found for women was owed to older respondents, were it was more pronounced and did not show up among the younger (where the average effect of BMI increase was effectively zero in the first place). Overall, we think that the additional differentiation between young-old and older-old added some interesting further findings that strengthens our argumentation and improved the paper. Thank you very much. Minor revision: "Figure legends are missing." We added a legend to Figure 1. Note on changes in the manuscript: To adequately address Reviewer 2's comment, we decided to include control variables at an earlier stage then we did in the original manuscript. This affected subsequent model specifications and particularly the decomposition of the confounding factors, as age is now already included in the reference model. This slightly changed the results and their interpretation, but arguably in a more meaningful direction as it now considers omitted variable bias when age is controlled for (which it typically is). As a consequence, parts of the results section had to be adapted. Note that all analyses involving asymmetric fixed effects models with controls are unaffected by this change. Specifically, this refers to the paragraphs on recovery and effect heterogeneity that remained unchanged. All changes applied to the manuscript are highlighted in red in the manuscript version with track changes. They are either a direct response to the reviewers or result from the model adjustments described. Also highlighted are changes correcting some copy editing errors we encountered (e.g. inconsistent use of tense or truncated numbers in the age range in table 1). Yours sincerely, Judith Kronschnabl, also on behalf of my co-authors Attachments Attachment Submitted filename: Response to Reviewers.pdf https://doi.org/10.1371/journal.pone.0249651.r002
23 Mar 2021 Decision Letter - David Meyre, Editor Bodyweight change and cognitive performance in the older population PONE-D-20-38422R1 Dear Dr. Kronschnabl, We’re pleased to inform you that your manuscript has been judged scientifically suitable for publication and will be formally accepted for publication once it meets all outstanding technical requirements. Within one week, you’ll receive an e-mail detailing the required amendments. When these have been addressed, you’ll receive a formal acceptance letter and your manuscript will be scheduled for publication. An invoice for payment will follow shortly after the formal acceptance. To ensure an efficient process, please log into Editorial Manager at http://www.editorialmanager.com/pone/, click the 'Update My Information' link at the top of the page, and double check that your user information is up-to-date. If you have any billing related questions, please contact our Author Billing department directly at authorbilling@plos.org. If your institution or institutions have a press office, please notify them about your upcoming paper to help maximize its impact. If they’ll be preparing press materials, please inform our press team as soon as possible -- no later than 48 hours after receiving the formal acceptance. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information, please contact onepress@plos.org. Kind regards, David Meyre Academic Editor PLOS ONE Additional Editor Comments (optional): Reviewers' comments: https://doi.org/10.1371/journal.pone.0249651.r003
Formally Accepted
25 Mar 2021 Acceptance Letter - David Meyre, Editor PONE-D-20-38422R1 Bodyweight change and cognitive performance in the older population Dear Dr. Kronschnabl: I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now with our production department. If your institution or institutions have a press office, please let them know about your upcoming paper now to help maximize its impact. If they'll be preparing press materials, please inform our press team within the next 48 hours. Your manuscript will remain under strict press embargo until 2 pm Eastern Time on the date of publication. For more information please contact onepress@plos.org. If we can help with anything else, please email us at plosone@plos.org. Thank you for submitting your work to PLOS ONE and supporting open access. Kind regards, PLOS ONE Editorial Office Staff on behalf of Dr. David Meyre Academic Editor PLOS ONE https://doi.org/10.1371/journal.pone.0249651.r004

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