Association between serum zinc and serum neurofilament light chains: A population-based analysis

Jun Wei; Ye Xu; Yang Liu

doi:10.1371/journal.pone.0326042

Peer Review History

Original SubmissionJanuary 10, 2025
10 Jan 2025 Author Response https://doi.org/10.1371/journal.pone.0326042.r001
Decision Letter - Huzaifa Umar, Editor PONE-D-25-01163 Association between serum zinc and serum neurofilament light chains: A population-based analysis PLOS ONE Dear Dr. Liu, 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 Jun 16 2025 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 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: Partly ******** 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? The PLOS Data policy requires authors to make all data underlying the findings described in their manuscript fully available without restriction, with rare exception (please refer to the Data Availability Statement in the manuscript PDF file). The data should be provided as part of the manuscript or its supporting information, or deposited to a public repository. For example, in addition to summary statistics, the data points behind means, medians and variance measures should be available. If there are restrictions on publicly sharing data—e.g. participant privacy or use of data from a third party—those must be specified. Reviewer #1: Yes Reviewer #2: Yes ****** 4. Is the manuscript presented in an intelligible fashion and written in standard English? PLOS ONE does not copyedit accepted manuscripts, so the language in submitted articles must be clear, correct, and unambiguous. 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: 1.technical and grammar are needed to be checked. 2. Percent of male and female was not presented in the study. 3. plagiarism report need to be submitted 4. two studies need to be acknowledged in this study; a- https://www.frontiersin.org/journals/aging-neuroscience/articles/10.3389/fnagi.2025.1517663/full b-https://pubmed.ncbi.nlm.nih.gov/32258830/ 5. Graphs or tables need to be added Reviewer #2: In this intriguing article, the authors investigated the association between serum zinc levels and serum neurofilament light chain (sNfL) levels in the general population, utilizing data from the National Health and Nutrition Examination Survey (NHANES) conducted in 2013-2014. Their analysis included a total population of 585 adults and revealed a significant negative association between serum zinc levels and sNfL, with a p-value at the margins of significance (0.0321). Stratified analyses indicated that this negative association was significant only among divorced, widowed, or separated individuals. Given these results, I believe the abstract's conclusion is somewhat overstated in asserting that serum zinc could serve as a novel predictor for the onset and progression of neurological disorders. Zinc is an essential micronutrient that plays various roles in the nervous system, and both its deficiency and excess can lead to several issues. In my opinion, the introduction is overly generic and should delve deeper into the essential activities in which zinc is involved within the nervous system. I would eliminate the sections pertaining to wound healing, tissue reconstruction, growth, and immune system function, as they are not directly relevant and rather superficial. Furthermore, the interaction between zinc intake and other micronutrients (such as copper) is not addressed. The potential association of copper deficiency myelopathy, which may arise as a complication of excessive zinc supplementation, should be cited (see DOI: 10.1001/archneur.61.5.762 and DOI: 10.1179/2045772314Y.0000000268). Other suggestions follow: - Smooth curve-fitting models revealed an L-shaped association between serum zinc levels and sNfL, as depicted in Figure 2. Threshold effect analyses (Table 3) indicated that the lowest threshold for a protective effect was 10.21 nmol/L (log-likelihood ratio < 0.001). However, even if not statistically significant, a careful observation of Figure 2 reveals an increase on the right side of the curve, with higher serum concentrations of zinc associating with increased levels of serum NfL. I believe this is important since excessive zinc intake has been associated with decreased concentrations of copper. - In the limitations section, it should be noted that for the size of the population, a significance level of p = 0.0321 is relatively low. - The explanation of the subgroup analyses, which revealed that the relationship between serum zinc and sNfL was particularly pronounced among divorced, widowed, or separated individuals, appears insufficiently incisive. It is appropriate to highlight that changes in marital status can influence the onset and progression of neurodegenerative diseases, but the possible mechanisms should be better specified. Are there data on the diet and potential micronutrient deficiencies in this population of individuals? - When discussing micronutrient and vitamin deficiencies and the incidence of disease, it should be acknowledged that low nutrient levels may reflect poor dietary habits, low levels of physical exercise, and can be influenced by many health factors, including body mass index. Therefore, micronutrient levels should not be considered solely as an indicator of nutritional status but also as a marker of overall health (e.g., for vitamin D, see DOI: 10.3390/nu7075111). ****** 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: Yes: Umar Muhammad Ghali Reviewer #2: Yes: Domenico Plantone ******** [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. 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Revision 1
8 May 2025 Author Response Reviewer #1: 1.technical and grammar are needed to be checked. Response: We appreciate the reviewer’s observation. The manuscript has been thoroughly revised for grammar, syntax, and technical clarity to ensure improved readability and language quality. 2. Percent of male and female was not presented in the study. Response: Thank you for this suggestion. We have added the percentage distribution of male (49.4%) and female (50.6%) participants in the Results section for greater clarity. 3. plagiarism report need to be submitted Response: We appreciate the opportunity to revise our manuscript. A plagiarism check was conducted using Turnitin, and the Similarity Index is 19%, which is within acceptable limits for originality. The plagiarism report has been submitted along with the revised manuscript for your reference. 4. two studies need to be acknowledged in this study; a- https://www.frontiersin.org/journals/aging-neuroscience/articles/10.3389/fnagi.2025.1517663/full b-https://pubmed.ncbi.nlm.nih.gov/32258830/ Response: We thank the reviewer for recommending these valuable references. Both studies have been carefully reviewed and are now appropriately cited in the second paragraph of the Discussion section to enhance the contextual background and support the mechanistic interpretation of our findings. 5. Graphs or tables need to be added Response: Thank you for this helpful suggestion. We have ensured that key findings are now appropriately presented in visual form. Specifically: A flowchart illustrating the participant selection process is provided (Figure 1). A smooth curve fitting plot depicting the nonlinear relationship between serum zinc and sNfL is presented (Figure 2). Detailed statistical outcomes are included in Tables 1–4. These additions enhance the readability and interpretability of the results. Reviewer #2: In this intriguing article, the authors investigated the association between serum zinc levels and serum neurofilament light chain (sNfL) levels in the general population, utilizing data from the National Health and Nutrition Examination Survey (NHANES) conducted in 2013-2014. Their analysis included a total population of 585 adults and revealed a significant negative association between serum zinc levels and sNfL, with a p-value at the margins of significance (0.0321). Stratified analyses indicated that this negative association was significant only among divorced, widowed, or separated individuals. Given these results, I believe the abstract's conclusion is somewhat overstated in asserting that serum zinc could serve as a novel predictor for the onset and progression of neurological disorders. Response: We thank the reviewer for this thoughtful and important comment. In response, we have revised the conclusion of the abstract to avoid overstatement. The updated sentence now reads: Our findings demonstrate an inverse association between serum zinc levels and sNfL concentrations among adults in the United States. This relationship is particularly pronounced in individuals who are divorced, widowed, or separated. We hope this revision better reflects the observational nature of our study and addresses the reviewer’s concern appropriately. Zinc is an essential micronutrient that plays various roles in the nervous system, and both its deficiency and excess can lead to several issues. In my opinion, the introduction is overly generic and should delve deeper into the essential activities in which zinc is involved within the nervous system. I would eliminate the sections pertaining to wound healing, tissue reconstruction, growth, and immune system function, as they are not directly relevant and rather superficial. Furthermore, the interaction between zinc intake and other micronutrients (such as copper) is not addressed. The potential association of copper deficiency myelopathy, which may arise as a complication of excessive zinc supplementation, should be cited (see DOI: 10.1001/archneur.61.5.762 and DOI: 10.1179/2045772314Y.0000000268). Response: We sincerely thank the reviewer for this insightful comment. In response: We have revised the introduction to focus more specifically on the role of zinc in the nervous system, emphasizing its regulation of synaptic plasticity and neurotransmission. General physiological roles unrelated to neurobiology—such as wound healing and immune function—have been removed to maintain thematic focus. We have also incorporated a discussion on zinc’s interaction with copper and highlighted the risk of copper deficiency myelopathy resulting from excessive zinc intake. The recommended references (DOI: 10.1001/archneur.61.5.762 and DOI: 10.1179/2045772314Y.0000000268) have been cited appropriately. We believe these revisions improve the scientific depth and focus of the manuscript. Other suggestions follow: Smooth curve-fitting models revealed an L-shaped association between serum zinc levels and sNfL, as depicted in Figure 2. Threshold effect analyses (Table 3) indicated that the lowest threshold for a protective effect was 10.21 nmol/L (log-likelihood ratio < 0.001). However, even if not statistically significant, a careful observation of Figure 2 reveals an increase on the right side of the curve, with higher serum concentrations of zinc associating with increased levels of serum NfL. I believe this is important since excessive zinc intake has been associated with decreased concentrations of copper. Response: We thank the reviewer for this valuable observation. In response, we have revised the Discussion section to acknowledge the slight upward trend in sNfL levels at higher serum zinc concentrations, as visible on the right side of the curve in Figure 2, despite the lack of statistical significance. We discussed the potential implications of this trend and referenced existing literature on zinc-induced copper deficiency and its neurological consequences, including copper deficiency myelopathy. The following references have been cited accordingly: Kumar N, Gross JB Jr, Kumar R. Copper deficiency myelopathy produces a clinical picture like subacute combined degeneration. Arch Neurol. 2004;61(5):762–765. doi:10.1001/archneur.61.5.762 These additions enhance the discussion by addressing possible risks of excessive zinc intake and the importance of maintaining optimal—not excessive—zinc levels for neurological health. In the limitations section, it should be noted that for the size of the population, a significance level of p = 0.0321 is relatively low. Response: We thank the reviewer for this thoughtful comment. In response, we have revised the Limitations section to note that the observed p-value (p = 0.0321), although statistically significant, may be relatively modest considering the sample size of the study. We now acknowledge that this finding should be interpreted with caution and highlight the need for larger-scale studies to confirm the observed association. The explanation of the subgroup analyses, which revealed that the relationship between serum zinc and sNfL was particularly pronounced among divorced, widowed, or separated individuals, appears insufficiently incisive. It is appropriate to highlight that changes in marital status can influence the onset and progression of neurodegenerative diseases, but the possible mechanisms should be better specified. Are there data on the diet and potential micronutrient deficiencies in this population of individuals? Response: We thank the reviewer for this thoughtful suggestion. In response, we have expanded the Discussion section to provide a more detailed explanation of the potential mechanisms underlying the pronounced association observed in divorced, widowed, or separated individuals. Specifically, we now discuss the possible roles of psychosocial stress, social isolation, and diet-related micronutrient deficiencies—factors that may contribute to increased vulnerability to neurodegenerative processes in this population. Existing literature supports the notion that individuals undergoing marital dissolution are at increased risk of poor diet quality and micronutrient deficiencies, which may further exacerbate neuronal decline. When discussing micronutrient and vitamin deficiencies and the incidence of disease, it should be acknowledged that low nutrient levels may reflect poor dietary habits, low levels of physical exercise, and can be influenced by many health factors, including body mass index. Therefore, micronutrient levels should not be considered solely as an indicator of nutritional status but also as a marker of overall health (e.g., for vitamin D, see DOI: 10.3390/nu7075111). Response: We thank the reviewer for this valuable and nuanced comment. In response, we have revised the Discussion section to acknowledge that micronutrient levels, including serum zinc, are influenced by a wide range of health-related factors beyond nutritional intake alone. Specifically, we now discuss how poor dietary habits, low physical activity, inflammation, comorbidities, and BMI can affect nutrient levels. As such, we emphasize that serum zinc should be interpreted not only as a marker of nutritional status, but also as a broader indicator of general health. We have also cited the suggested reference on vitamin D as a representative example (DOI: 10.3390/nu7075111). Attachments Attachment Submitted filename: Response to Reviewers.docx https://doi.org/10.1371/journal.pone.0326042.r003
Decision Letter - Huzaifa Umar, Editor <p>Association between serum zinc and serum neurofilament light chains: A population-based analysis PONE-D-25-01163R1 Dear Dr. Yang Liu, 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 will be generated when your article is formally accepted. Please note, if your institution has a publishing partnership with PLOS and your article meets the relevant criteria, all or part of your publication costs will be covered. Please make sure your user information is up-to-date by logging into Editorial Manager at Editorial Manager® and clicking the ‘Update My Information' link at the top of the page. If you have any questions relating to publication charges, 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, Huzaifa Umar Academic Editor PLOS ONE Additional Editor Comments (optional): Reviewers' comments: https://doi.org/10.1371/journal.pone.0326042.r004
Formally Accepted
Acceptance Letter - Huzaifa Umar, Editor PONE-D-25-01163R1 PLOS ONE Dear Dr. Liu, I'm pleased to inform you that your manuscript has been deemed suitable for publication in PLOS ONE. Congratulations! Your manuscript is now being handed over to our production team. At this stage, our production department will prepare your paper for publication. This includes ensuring the following: * All references, tables, and figures are properly cited * All relevant supporting information is included in the manuscript submission, * There are no issues that prevent the paper from being properly typeset You will receive further instructions from the production team, including instructions on how to review your proof when it is ready. Please keep in mind that we are working through a large volume of accepted articles, so please give us a few days to review your paper and let you know the next and final steps. Lastly, 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 customercare@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. Huzaifa Umar Academic Editor PLOS ONE https://doi.org/10.1371/journal.pone.0326042.r005

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