The Effects of Vitamin D Replacement with a High-Dose Treat-to-Goal Strategy

Round 1

Reviewer 1 Report

Comments and Suggestions for Authors

In the present manuscript entitled "The Effects of Vitamin D Replacement with a High Dose Treat to Goal Strategy" authors have retrospectively reviewed a clinical vitamin D replacement strategy that was used over 5 years in a large real-world patient population in Greece, and found that their strategy is successful in replenishing vitamin D stores without significant toxicities. It is of great interest to the Nutrients journal audience.   Despite the highly successful results reported, several points require further discussion, before this work could be suitable for publication.

1. The baseline vitamin D levels were not measured during the same month of the year for the entire population. This could allow for some variation in both the baseline and the treatment-induced concentrations. Please comment.
2. Some patients included in the analysis were treated with vitamin D replacement for osteoporosis/low bone mass, while others solely for replacement purposes. Was there any difference to be reported in this work?
3. No data on fractures are reported. Are these available? Will they be reported separately?
4. In the intervention arm, was there any variation in the increments in serum vitamin D concentrations based on clinical predictors (baseline D, BMI, other)? Will these be reported in other works?
5. Do you have data on infections, psychiatric disorders or other potential off-target effects of vitamin D replacement?
6. Do you have data on PTH concentrations or bone mineral density measures?
7. Would you have data in patients aiming for a 25-OH-D concentration >20ng/ml?

Author Response

In the present manuscript entitled "The Effects of Vitamin D Replacement with a High Dose Treat to Goal Strategy" authors have retrospectively reviewed a clinical vitamin D replacement strategy that was used over 5 years in a large real-world patient population in Greece, and found that their strategy is successful in replenishing vitamin D stores without significant toxicities. It is of great interest to the Nutrients journal audience.   Despite the highly successful results reported, several points require further discussion, before this work could be suitable for publication.

1. The baseline vitamin D levels were not measured during the same month of the year for the entire population. This could allow for some variation in both the baseline and the treatment-induced concentrations. Please comment.

Response: Thank you for this excellent remark. We added this to the limitations of our study.

2. Some patients included in the analysis were treated with vitamin D replacement for osteoporosis/low bone mass, while others solely for replacement purposes. Was there any difference to be reported in this work?

Response: Thank you for this excellent remark. As we mention in our Results section in lines 253-255: the intervention subjects were older and had more commonly pre-existing diagnosis of osteoporosis or osteopenia (p<0.001). A specific analysis in this population, will be prepared and presented in a future manuscript, along with fractures data.

3. No data on fractures are reported. Are these available? Will they be reported separately?

Response: As mentioned in the prior response (Comment #2), a manuscript containing fractures data will be prepared for the osteoporosis population separately in the future, together with data on fractures on patients treated solely for replenishment purposes – which are not available at the moment for analysis.

4. In the intervention arm, was there any variation in the increments in serum vitamin D concentrations based on clinical predictors (baseline D, BMI, other)? Will these be reported in other works?

Response: Thank you for the excellent comment. A future work will focus specifically on clinical factors affecting the changes in vitamin D concentration and how could these be used to alter the loading or maintenance dose effectively. A note was added in our study’s limitations.

5. Do you have data on infections, psychiatric disorders or other potential off-target effects of vitamin D replacement?

Response: Unfortunately, we have no data on infections, psychiatric disorders of other off-target effects of vitamin D replacement. We mentioned this in the limitations section.

6. Do you have data on PTH concentrations or bone mineral density measures?

Response: Thank you for the excellent question. PTH concentrations are available in some, but not all patients reviewed in this work. Once this data set is analyzed, we will submit a separate manuscript to your esteemed journal.

7. Would you have data in patients aiming for a 25-OH-D concentration >20ng/ml?

Response: Even though, some scholars aim for 25-D concentrations >20ng/ml in the general population, our group adheres to the original 2011 Endocrine Society Clinical Practice Guidelines Recommendations aiming for a concentration >30ng/ml. In order to facilitate the interpretation of our results from colleagues aiming for lower concentrations, we added an ad hoc analysis explaining the success rates by time point in case the 20ng/ml threshold were to be used. Please see lines 312-317 stating that: “A second ad hoc analysis was performed to estimate the rates of adequacy of vitamin D, if a threshold of 20ng/ml were to be used in the intervention population. In that scenario, treatment success would be found in 3953/3987 (99.1%) measurements, while treatment failure would only be observed in 9/1544 (0.6%) patients at 2 months, 6/894 (0.7%) at 1 year, 7/621 (1.1%) at 2 years, 8/436 (1.8%) at 3 years, 1/290 (0.3%) at 4 years and 3/200 (1.5%) at 5 years.”

Reviewer 2 Report

Comments and Suggestions for Authors

This article presents a study the authors conducted to restore recommended vitamin D levels, i.e., 30 ng/ml – 100 ng/ml. The protocol is treat-to-target, including an initial loading dose and a subsequent maintenance dose, with periodic measurement of blood 25(OH)D levels and adjustments if necessary. Their data show that this protocol can effectively achieve this goal without increasing the risk of side effects, including hypervitaminosis, nephrolithiasis, or renal colic. The overall success rate was 91%. Treat-target is important because many clinical trials using vitamin D supplementation to treat various diseases have failed to generate conclusive evidence, at least in part because dosing regimens did not account for actual blood 25(OH)D levels. The protocol presented is interesting and doable. However, the study's contribution to this field is limited in its current form because it does not demonstrate that such a protocol benefits patients with diseases.

Author Response

REVIEWER #2

This article presents a study the authors conducted to restore recommended vitamin D levels, i.e., 30 ng/ml – 100 ng/ml. The protocol is treat-to-target, including an initial loading dose and a subsequent maintenance dose, with periodic measurement of blood 25(OH)D levels and adjustments if necessary. Their data show that this protocol can effectively achieve this goal without increasing the risk of side effects, including hypervitaminosis, nephrolithiasis, or renal colic. The overall success rate was 91%. Treat-target is important because many clinical trials using vitamin D supplementation to treat various diseases have failed to generate conclusive evidence, at least in part because dosing regimens did not account for actual blood 25(OH)D levels. The protocol presented is interesting and doable. However, the study's contribution to this field is limited in its current form because it does not demonstrate that such a protocol benefits patients with diseases.

Response: Thank you for your excellent remarks. Our work is a quality-control study aiming to identify a treatment protocol that would work in restoring vitamin D adequacy, and based on your kind comments, we feel that we achieved it. This could guide clinicians with similar patients design their own interventions, if their goal is the same.

Whether vitamin D treatment is needed and helpful to treat diseases, falls outside the scope of the present manuscript, but we would be happy to submit our findings in future works in this esteemed journal.

However, we added this important limitation as indicated in lines 498-500: “the study’ s contribution to this field is limited in its current form, because it does not demonstrate that such a protocol benefits patients with specific diseases.”

Reviewer 3 Report

Comments and Suggestions for Authors

Thank you for the invitation to review this manuscript. The article addresses the highly prevalent and clinically relevant issue of vitamin D deficiency and proposes a long-term treat-to-target supplementation protocol. The scope of the work appears to be the evaluation of the effectiveness and safety of a structured vitamin D replacement strategy compared with no supplementation, using real-world longitudinal data over several years. 

ABSTRACT

1. The abstract clearly conveys the clinical problem, intervention, comparison group, and primary outcomes. However, its content density is very high, particularly in the Methods section. You may consider simplifying the dosing protocol description by focusing on its underlying logic (dose stratification based on baseline 25(OH)D levels) and referring readers to the main text for exact dosing schedules, thereby improving readability and accessibility.
2. The definition of vitamin D deficiency using a threshold of <30 ng/ml should ideally be briefly justified or contextualized, as this cutoff remains debated in the literature. A brief clarification would strengthen the study's scientific positioning and pre-empt potential criticism.
3. The description of the control group (“patients who never took vitamin D supplements”) would benefit from clarification regarding how this status was ascertained (e.g., self-report, prescription records). This is important to assess the robustness of the comparison and potential misclassification bias.
4. The Results section is strong in reporting both effectiveness and safety outcomes. Nonetheless, presenting absolute values for mean 25(OH)D concentrations (in addition to adequacy rates and p-values) would help readers better appreciate the clinical magnitude of the intervention’s effect.
5. The conclusion appropriately reflects the findings. Still, the claim of “no adverse events” could be softened to better align with the reported data (e.g., “no increase in adverse events compared with controls”), thereby avoiding overgeneralization.

INTRODUCTION

6. The introduction provides a clear biological and clinical rationale for vitamin D supplementation and appropriately situates the problem within modern lifestyle constraints. However, the opening paragraph could be strengthened by briefly articulating the clinical consequences of vitamin D deficiency (e.g., skeletal and extra-skeletal outcomes), which would further justify the need for an optimized long-term replacement strategy.
7. The manuscript cites multiple authoritative guidelines that define deficiency and recommend supplementation, which strengthens its foundation. Nonetheless, the text would benefit from a clearer synthesis of these recommendations, explicitly highlighting the existing gaps or inconsistencies (e.g., dosing limits versus target serum levels) that motivate the development of a treat-to-target protocol.
8. The reference to previous work demonstrating the inefficacy of low-dose vitamin D supplementation is highly relevant. Expanding on this point with a brief description of the study design or key findings (e.g., the proportion remaining deficient, the duration of supplementation) would help readers better understand how this prior evidence directly informed the current intervention.
9. The transition from guideline recommendations to the authors’ proposed protocol is logical but could be more explicit. Stating more clearly why existing guideline-based approaches may fail in real-world practice (e.g., adherence issues, interindividual variability, seasonal effects) would strengthen the justification for the new strategy.
10. The final sentence appropriately defines the study aim; however, explicitly stating the primary outcomes (vitamin D adequacy and safety endpoints) would improve clarity and align the introduction more closely with the results presented later in the manuscript.

MATERIALS AND METHODS

11. The description of the Hellenic Endocrine Network is informative. Still, the section would benefit from explicitly stating whether participating clinics followed identical clinical record systems and follow-up schedules, as heterogeneity in routine practice could influence outcome assessment in a retrospective design.
12. Consider clarifying whether the treatment algorithm was prospectively standardized across all clinics or retrospectively applied during data extraction, as this distinction is essential for internal validity.
13. The definition of the control group may introduce selection bias, as controls include patients who declined supplementation and those who self-supplemented at low doses; a brief justification for grouping these individuals, or a sensitivity analysis plan, would strengthen the methodological rationale.
14. A single condensed note on language: there are minor inconsistencies in terminology (e.g., “25(OH)D,” “vitamin D,” and “25-OH-vitamin D”) that could be harmonized for clarity.
15. The retrospective quality-control framework is appropriate, but the authors should specify whether a predefined data collection form or protocol was used to ensure consistency across the four clinics.
16. It would be helpful to clarify how missing data were handled, particularly for long-term vitamin D measurements over the 5-year follow-up, as attrition may influence longitudinal comparisons.
17. The rationale for selecting the specific follow-up time points (2 months, then annually up to 5 years) should be briefly justified, especially in relation to expected pharmacokinetics and clinical monitoring practices.
18. The loading-dose stratification based on baseline vitamin D levels is clearly presented; however, citing clinical guidelines or prior evidence supporting these thresholds and dosing choices would strengthen the scientific grounding of the protocol.
19. Allowing patients complete discretion regarding timing and days of administration may introduce variability in adherence and absorption; the authors may wish to acknowledge this explicitly as a potential limitation.
20. The decision not to retest vitamin D levels after dose adjustments for under- or over-replacement warrants further justification, as this deviates from standard monitoring practices and has implications for safety assessment.
21. The primary and secondary outcomes are well defined; nonetheless, it would be helpful to specify whether outcome assessors were blinded to group allocation during data abstraction to reduce information bias.
22. The combined safety outcome is clinically relevant, but a brief rationale for combining these renal endpoints into a single composite measure would help readers interpret its significance.
23. The definition of hypervitaminosis D using a laboratory threshold is clear, though a short justification for selecting >150 ng/ml (rather than lower thresholds sometimes used clinically) would be valuable.
24. The exclusion criteria are comprehensive and appropriate for isolating the effects of the protocol; however, the authors should indicate how consistently adherence (<80%) was documented across clinics, given reliance on self-report and prescription records.
25. Excluding patients with altered gastrointestinal absorption is methodologically sound, but this also limits generalizability; acknowledging this trade-off would strengthen transparency.
26. Consider clarifying whether exclusions were applied before or after group allocation to avoid ambiguity regarding sample derivation.
27. The statistical methods are generally appropriate; however, the authors should clarify whether adjustments for multiple comparisons were considered, given repeated measurements across several time points.
28. It would be helpful to specify whether analyses were performed per-protocol or intention-to-treat, particularly in light of exclusions for adherence and follow-up completeness.
29. Reporting how confounding variables (e.g., age, BMI, baseline vitamin D levels) were handled—whether through stratification or multivariable analysis—would enhance interpretability of the results.

RESULTS

The results description must be updated in accordance with the proposed modifications to the methods, as needed.

DISCUSSION

30. The opening paragraph clearly summarizes the study design and principal findings; however, the tone may benefit from slight moderation, particularly where terms such as “impressive” and “extremely high” are used, to maintain a more neutral, academic framing of the results.
31. The comparison between the intervention and control groups would be strengthened by a more explicit acknowledgment of baseline behavioral and motivational differences between treated patients and controls, as these factors may partially explain observed efficacy.
32. The claim that this is the first study to test a “novel treat-to-target strategy” should be supported by a brief clarification of how this approach differs substantively from prior high-dose or loading-dose regimens reported in the literature.
33. The linkage to the authors’ prior work is well articulated and provides continuity; nevertheless, explicitly distinguishing hypothesis-generating findings from confirmatory conclusions would improve scientific rigor.
34. The discussion of vitamin D deficiency definitions and associated outcomes is comprehensive. Still, the authors may consider streamlining this section to more directly support the rationale for targeting ≥30 ng/ml, rather than broadly reviewing deficiency-related risks.
35. When referencing the Endocrine Society guideline, it would be helpful to briefly acknowledge more recent debates or guideline updates to demonstrate awareness of evolving consensus and ongoing controversy in the field.
36. The detailed description of the loading-dose totals is informative; however, relocating some numerical detail to a table or supplementary material could improve narrative flow in the Discussion.
37. The safety interpretation is generally balanced, though the assertion that efficacy “surpassed significantly any previously reported replacement method” may be too strong without a formal comparative framework or systematic review.

CONCLUSIONS

38. The conclusion effectively reiterates the global burden of vitamin D deficiency; however, the opening sentence could be strengthened by more precisely linking prevalence to the unmet need for practical, scalable treatment strategies.
39. The statement that the protocol “appears promising” is appropriately cautious. Yet, the conclusion would benefit from explicitly restating that the evidence derives from a retrospective, real-world analysis, to avoid overgeneralization.
40. Consider briefly emphasizing the key strengths of the protocol—such as simplicity, treat-to-target design, and long-term follow-up—while maintaining restraint in claims regarding efficacy and safety.
41. The call for future research is appropriate; specifying the need for prospective randomized or parallel-arm comparative studies, and ideally including clinically meaningful endpoints beyond biochemical adequacy, would further strengthen this closing section.

Thank you again for the opportunity to review this work. The study addresses a significant gap in long-term vitamin D management and, with some refinement in clarity and framing, has the potential to make a meaningful contribution to the field.

Comments on the Quality of English Language

I believe minor revisions are required before the Editor decides whether to accept it.

Author Response

REVIEWER #3

Thank you for the invitation to review this manuscript. The article addresses the highly prevalent and clinically relevant issue of vitamin D deficiency and proposes a long-term treat-to-target supplementation protocol. The scope of the work appears to be the evaluation of the effectiveness and safety of a structured vitamin D replacement strategy compared with no supplementation, using real-world longitudinal data over several years. 

ABSTRACT

1. The abstract clearly conveys the clinical problem, intervention, comparison group, and primary outcomes. However, its content density is very high, particularly in the Methods section. You may consider simplifying the dosing protocol description by focusing on its underlying logic (dose stratification based on baseline 25(OH)D levels) and referring readers to the main text for exact dosing schedules, thereby improving readability and accessibility.

Response: Thank you for the excellent comment. Given that the “Nutrients” journal is open-access, and readers can refer to the full-text version, this is a truly helpful suggestion. Done as instructed: in line 35 we added the following “Please refer to the main text for loading and maintenance dose titration.”

1. The definition of vitamin D deficiency using a threshold of <30 ng/ml should ideally be briefly justified or contextualized, as this cutoff remains debated in the literature. A brief clarification would strengthen the study's scientific positioning and pre-empt potential criticism.

Response: Thank you for pointing this out. We added the following sentence in lines 25-26 of the abstract about it: “Despite different cutoffs used to define it, many clinicians adhere to this 2011 Endocrine Society’s definition.”

1. The description of the control group (“patients who never took vitamin D supplements”) would benefit from clarification regarding how this status was ascertained (e.g., self-report, prescription records). This is important to assess the robustness of the comparison and potential misclassification bias.

Response: Thank you for your comment. We changed lines 26-30 accordingly stating that: We present a special treat-to-target protocol aiming to restore and maintain vitamin D sufficiency. Methods: We reviewed the efficacy and safety of our vitamin D supplementation protocol over 5 years, compared to a group of patients who self-reported never taking vitamin D supplements.

1. The Results section is strong in reporting both effectiveness and safety outcomes. Nonetheless, presenting absolute values for mean 25(OH)D concentrations (in addition to adequacy rates and p-values) would help readers better appreciate the clinical magnitude of the intervention’s effect.

Response: Done as instructed. Please see the following change in lines 38-42: “Baseline vitamin D concentrations of 22.6 ng/ml (controls) did not change significantly (2 months: 22.2; 1 year: 21.7; 2 years: 22.0; 3 years: 23.8; 4 years: 21.8 and 5 years: 22.1 ng/ml), while concentrations of 21.9 ng/ml (intervention group) reached and stayed around 40ng/ml (2 months: 41.0; 1 year: 39.4; 2 years: 39.0; 3 years: 39.3; 4 years: 40.4 and 5 years: 39.4 ng/ml).”

1. The conclusion appropriately reflects the findings. Still, the claim of “no adverse events” could be softened to better align with the reported data (e.g., “no increase in adverse events compared with controls”), thereby avoiding overgeneralization.

Response: Thank you for the excellent suggestion. Done as proposed – please refer to lines 58-59 addition: “with no increase in adverse events compared with controls”.

INTRODUCTION

1. The introduction provides a clear biological and clinical rationale for vitamin D supplementation and appropriately situates the problem within modern lifestyle constraints. However, the opening paragraph could be strengthened by briefly articulating the clinical consequences of vitamin D deficiency (e.g., skeletal and extra-skeletal outcomes), which would further justify the need for an optimized long-term replacement strategy.

Response: We strongly agree and have added a few lines with several citations in that regard in lines 68-74: “Vitamin D deficiency has been linked to multiple adverse skeletal effects including secondary hyperparathyroidism, bone loss, and increased risk of fractures in older adults. Moreover, significant extra-skeletal effects on the immune system, including the risk and severity of infectious diseases, metabolic abnormalities, including the risk for development of type 2 diabetes mellitus and disease control, cardiovascular events and mortality and psychiatric disorders have been described.”

1. The manuscript cites multiple authoritative guidelines that define deficiency and recommend supplementation, which strengthens its foundation. Nonetheless, the text would benefit from a clearer synthesis of these recommendations, explicitly highlighting the existing gaps or inconsistencies (e.g., dosing limits versus target serum levels) that motivate the development of a treat-to-target protocol.

Response: We agree with your comment and added a sentence in that regard in lines 81-82 claiming that “In these guidelines, dosing limits and target serum levels are not well connected or related to the pre-existing degree of this nutrient’s deficiency.”

1. The reference to previous work demonstrating the inefficacy of low-dose vitamin D supplementation is highly relevant. Expanding on this point with a brief description of the study design or key findings (e.g., the proportion remaining deficient, the duration of supplementation) would help readers better understand how this prior evidence directly informed the current intervention.

Response: We are thankful for this comment. We expanded that section in lines 88-93, stating that: “Moreover, not many studies have assessed a specific treat-to-target strategy aiming to re-store adequacy in a consistent, long-term mode. In a previously published work from our group, including 6912 subjects with vitamin D deficiency, patients on-treatment continu-ously for more than 12 months with low (≤1200 IU daily), medium (1200–3000 IU daily) and high (>3000 IU daily) doses of vitamin D supplements achieved vitamin D adequacy in 42.3%, 55.5 and 68.0% respectively.”

1. The transition from guideline recommendations to the authors’ proposed protocol is logical but could be more explicit. Stating more clearly why existing guideline-based approaches may fail in real-world practice (e.g., adherence issues, interindividual variability, seasonal effects) would strengthen the justification for the new strategy.

Response: We agree and have added a sentence in that regard in lines 83-85: “It is noteworthy that a complex interplay of adherence issues, interindividual variability, and seasonal effects negatively impacts both population-level and patient-specific vitamin D concentrations in most countries.”

1. The final sentence appropriately defines the study aim; however, explicitly stating the primary outcomes (vitamin D adequacy and safety endpoints) would improve clarity and align the introduction more closely with the results presented later in the manuscript.

Response: Agree with the comment. Done as proposed in lines 95-98: The present study assesses the efficacy (vitamin D adequacy, i.e. 25-OH-D ≥30ng/ml) and safety (risk of nephrolithiasis, renal colics, hypervitaminosis D) of this replacement strategy, in a retrospective, quality-control manner.

 

MATERIALS AND METHODS

1. The description of the Hellenic Endocrine Network is informative. Still, the section would benefit from explicitly stating whether participating clinics followed identical clinical record systems and follow-up schedules, as heterogeneity in routine practice could influence outcome assessment in a retrospective design.

Response: Our Network includes >50 clinics all over the nation. The clinics participating in the present study followed the same procedures. This was explicitly stated in the Methods section in lines 105-116: “and it was subsequently followed by the present study’s participating clinics, including an identical clinical record systems and follow-up schedule.” Thank you for your comment.

1. Consider clarifying whether the treatment algorithm was prospectively standardized across all clinics or retrospectively applied during data extraction, as this distinction is essential for internal validity.

Comment: This protocol was designed prior to the treatment initiation. It was not applied during data extraction. This was clarified in the Methods section in lines 105-116: “and it was subsequently followed by the present study’s participating clinics, including an identical clinical record systems and follow-up schedule.” Thank you for your comment.

1. The definition of the control group may introduce selection bias, as controls include patients who declined supplementation and those who self-supplemented at low doses; a brief justification for grouping these individuals, or a sensitivity analysis plan, would strengthen the methodological rationale.

Response: Thank you for pointing this out. We added a sentence in lines 141-144 pointing out that “The later were included in the control group, because they are known to achieve minimal rates of vitamin D adequacy (28.2% when using < 1,200 IU daily for up to 12 months), based on our prior studies and are not expected to affect treatment outcomes.”

1. A single condensed note on language: there are minor inconsistencies in terminology (e.g., “25(OH)D,” “vitamin D,” and “25-OH-vitamin D”) that could be harmonized for clarity.

Response: Thank you for noting this. We edited it to include vitamin D as the preferred term.

1. The retrospective quality-control framework is appropriate, but the authors should specify whether a predefined data collection form or protocol was used to ensure consistency across the four clinics.

Response: A specific data collection form was designed, after these patients were clinically treated, therefore, when we started collecting these data in a retrospective manner. This in now clarified in the methods section in line 153.

1. It would be helpful to clarify how missing data were handled, particularly for long-term vitamin D measurements over the 5-year follow-up, as attrition may influence longitudinal comparisons.

Response: We did not impute missing data, and any missing data are not expected to influence statistical outcomes, due to the large number of patients included. We added a sentence explaining that in the methods section.

1. The rationale for selecting the specific follow-up time points (2 months, then annually up to 5 years) should be briefly justified, especially in relation to expected pharmacokinetics and clinical monitoring practices.

Response: The rationale of the timeline was added in the methods section in line 162 “Missing data imputation was not used.”

1. The loading-dose stratification based on baseline vitamin D levels is clearly presented; however, citing clinical guidelines or prior evidence supporting these thresholds and dosing choices would strengthen the scientific grounding of the protocol.

Response: A sentence was added citing the 2011 Clinical Practice Committee Guideline of the Endocrine Society in lines 129-135: “The rationale of the present protocol was to rapidly replenish deficient levels, ensuring optimal serum concentrations for bone 6 and other potential health benefits, while follow-up with a long-term maintenance dose and yearly measurements would allow for individualized adjustments to sustain optimal levels. while preventing toxicity or un-der-supplementation. The dose of our vitamin D supplements falls well within the reference provided by the 2011 Endocrine Society’s Clinical Practice Guideline for patients at risk for vitamin D deficiency.”

1. Allowing patients complete discretion regarding timing and days of administration may introduce variability in adherence and absorption; the authors may wish to acknowledge this explicitly as a potential limitation.

Response: Thank you for pointing this out. We added this as a limitation in our discussion section.

1. The decision not to retest vitamin D levels after dose adjustments for under- or over-replacement warrants further justification, as this deviates from standard monitoring practices and has implications for safety assessment.

Response: The 2011 Endocrine Society’s clinical practice guidelines propose the use of similar doses of vitamin D supplements without any monitoring in patients at risk for vitamin D deficiency, without fear of significant risks. A comment was added in the text in lines 183-190: “The decision to avoid retesting in these cases, aimed to prevent patient burden and medical care expenses and was based on the knowledge that such doses have not been associated with risks for vitamin D toxicity, when used for only two months (dose increments) and discontinuation of all supplements for 6 months provides adequate time periods to return vitamin D concentration to the deficiency range, or the lowest end of adequacy, especially given that such doses have been recommended for use in the long term in patients at risk for vitamin D deficiency (not those with a known deficiency). “  

1. The primary and secondary outcomes are well defined; nonetheless, it would be helpful to specify whether outcome assessors were blinded to group allocation during data abstraction to reduce information bias.

Response: Indeed, the outcome assessors were blinded to group allocation during data abstraction to reduce information bias. A comment was added in lines 204-206: “The outcome assessors were blinded to group allocation during data abstraction to reduce information bias.”

1. The combined safety outcome is clinically relevant, but a brief rationale for combining these renal endpoints into a single composite measure would help readers interpret its significance.

Response: The combination was used to allow for statistically significant effects to emerge if small numbers of events would occur, to avoid bias. A note was made in line 203: “in case small numbers of events would tend to mask a statistically significant trend”

1. The definition of hypervitaminosis D using a laboratory threshold is clear, though a short justification for selecting >150 ng/ml (rather than lower thresholds sometimes used clinically) would be valuable.

Response: Thank you for the excellent comment. The present work follows the 2011 Endocrine Society CPGC, where vitamin D sufficiency is defined as a serum 25-hydroxyvitamin D [25(OH)D] ≥ 30 ng/mL, and vitamin D toxicity is generally associated with 25(OH)D concentrations > 150 ng/ml. We acknowledged in our edits that the vitamin D toxicity threshold is not universally accepted as that, given that some colleagues support the notion that values >240 ng/ml are required to displace 25-D towards 1,25 (OH)₂-D (Vieth et al, JBMR 2007), while others support that serum concentrations >80 ng/ml are needed before vitamin D toxicity could ensue (Tebben et al. Endocr Rev 2016).

We added the following text in lines 204-210: “The threshold we used for defining toxicity is based on the 2011 Endocrine Society Clinical Practice Guidelines, but this is not universally accepted as such: some studies suggest that serum 25-OH vitamin D concentrations have to surpass 240 ng/ml before 1,25-(OH)₂-vitamin D production increases, while others suggest that 25-OH vitamin D concentrations above 80 ng/ml could produce toxicity in some individuals.”

1. The exclusion criteria are comprehensive and appropriate for isolating the effects of the protocol; however, the authors should indicate how consistently adherence (<80%) was documented across clinics, given reliance on self-report and prescription records.

Response: Thank you for this comment. This number is available in “Figure 2, Study Flowsheet”, where inconsistent intake was the reason for patients’ exclusion in n=3,291 cases, i.e. 54.2% of our excluded patients.

1. Excluding patients with altered gastrointestinal absorption is methodologically sound, but this also limits generalizability; acknowledging this trade-off would strengthen transparency.

Response: Thank you for pointing this. We added a sentence in the limitations section of our discussion in lines 435-437: “Of course, these effects cannot be extrapolated to patients with history of gastrointestinal surgeries leading to malabsorption or other malabsorptive conditions, since those were excluded from our study.”

1. Consider clarifying whether exclusions were applied before or after group allocation to avoid ambiguity regarding sample derivation.

Response: Thank you for your comment. We added a clarification in the appropriate section in line 223: “The exclusion criteria were applied prior to patients’ group allocation.”

1. The statistical methods are generally appropriate; however, the authors should clarify whether adjustments for multiple comparisons were considered, given repeated measurements across several time points.

Response: Thank you for your noticing this missing point. Post-tests were performed in all analyses where multiple comparisons were made. We also added the Friedman test in our list in lines 232-234: “and Friedman tests; specific post-tests for multiple comparisons were also performed, where applicable. Per protocol analysis was performed, while intention-to-treat analysis was not performed, given the study exclusions.”

1. It would be helpful to specify whether analyses were performed per-protocol or intention-to-treat, particularly in light of exclusions for adherence and follow-up completeness.

Response: Thank you for your comment. A clarification was added in lines 234-235: “Per protocol analysis was performed, while intention-to-treat analysis was not performed, given the study exclusions.”

1. Reporting how confounding variables (e.g., age, BMI, baseline vitamin D levels) were handled—whether through stratification or multivariable analysis—would enhance interpretability of the results.

Response: Thank you for this excellent comment. These need to be addressed in a separate manuscript, which is being prepared, and focuses exactly in these details.

 

RESULTS

The results description must be updated in accordance with the proposed modifications to the methods, as needed.

Response: Thank you for the detailed review of our work. We adjusted accordingly where needed.

DISCUSSION

1. The opening paragraph clearly summarizes the study design and principal findings; however, the tone may benefit from slight moderation, particularly where terms such as “impressive” and “extremely high” are used, to maintain a more neutral, academic framing of the results.

Response: Thank you for this comment. We removed such phrases. If more is found, please notify us again.

1. The comparison between the intervention and control groups would be strengthened by a more explicit acknowledgment of baseline behavioral and motivational differences between treated patients and controls, as these factors may partially explain observed efficacy.

Response: Thank you for pointing this. We fully agree with this comment and added a sentence on that in lines 350-351: “Obviously, baseline behavioral and motivational differences between treated patients and controls may partially explain the observed efficacy.”

1. The claim that this is the first study to test a “novel treat-to-target strategy” should be supported by a brief clarification of how this approach differs substantively from prior high-dose or loading-dose regimens reported in the literature.

Response: We thank the reviewer for this comment. We agree that clarification is warranted. We have revised the manuscript to explicitly state this distinction and to clarify that the novelty lies in the long-term, iterative, target-guided nature of the protocol, rather than in the use of high doses alone in lines 339-348: ”Its novelty is based on its structured, goal-driven protocol with predefined biochemical targets and mandatory reassessment, rather than the use of high or loading doses per se. In contrast to prior studies that employed fixed high-dose or loading-dose regimens without systematic dose recalibration, our strategy is distinguished by: (i) baseline 25(OH)D–stratified loading doses, (ii) mandatory reassessment at 2 months, (iii) explicit biochemical targets (25(OH)D ≥30 ng/mL, with dose de-escalation at ≥40 ng/mL, and (iv) long-term maintenance with annual monitoring and protocolized dose adjustments over up to 5 years. Previous high-dose or loading-dose regimens have generally focused on short-term repletion or fixed dosing schemes ^23,24 and have not incorporated sustained, algorithm-based titration aimed at maintaining long-term adequacy.”

1. The linkage to the authors’ prior work is well articulated and provides continuity; nevertheless, explicitly distinguishing hypothesis-generating findings from confirmatory conclusions would improve scientific rigor.

Response:  We thank the reviewer for this important suggestion. We agree that clearer differentiation between hypothesis-generating observations and confirmatory conclusions strengthens the scientific rigor of the manuscript. Accordingly, we have revised the Discussion and Conclusions to explicitly frame our findings as confirmatory with respect to feasibility, efficacy, and safety of a treat-to-target vitamin D replacement strategy in a real-world setting, while clearly identifying mechanistic implications, long-term clinical outcome inferences, and generalizability beyond similar populations as hypothesis-generating. In the final part of our discussion section, in lines 422-426 we explicitly state that: “Obviously, given the retrospective design and absence of randomization, the study con-firms the protocol’s effectiveness in achieving and maintaining biochemical vitamin D adequacy, but causal inferences regarding clinical endpoints and superiority over other regimens require prospective, randomized evaluation..” This distinction has been incorporated to better align conclusions with the evidentiary strength of the data.

1. The discussion of vitamin D deficiency definitions and associated outcomes is comprehensive. Still, the authors may consider streamlining this section to more directly support the rationale for targeting ≥30 ng/ml, rather than broadly reviewing deficiency-related risks.

Response: We thank the reviewer for this constructive comment. We agree that the Discussion can be more focused in directly supporting the rationale for targeting a serum 25(OH)D concentration ≥30 ng/mL. Accordingly, we have streamlined this section by reducing the breadth of the general review on deficiency-associated risks and sharpening the emphasis on evidence and guideline-based positions that specifically support the ≥30 ng/mL threshold as a clinically relevant target. The revised text now more directly links this cutoff to skeletal outcomes, suppression of secondary hyperparathyroidism, and its adoption by major professional societies, while retaining only the most pertinent extra-skeletal associations to contextualize the choice of target. This revision improves clarity and ensures closer alignment between the background discussion and the study’s treat-to-target rationale.

1. When referencing the Endocrine Society guideline, it would be helpful to briefly acknowledge more recent debates or guideline updates to demonstrate awareness of evolving consensus and ongoing controversy in the field.

Response: We agree that there remains substantial controversy in the field and we added a sentence in that regard in the discussion section as below in lines 378-380: “Other clinical practice guidelines recommend treatment of vitamin D deficient individuals with a goal of adequacy (>30 ng/ml), only in specific populations, such as those with osteoporosis.”

1. The detailed description of the loading-dose totals is informative; however, relocating some numerical detail to a table or supplementary material could improve narrative flow in the Discussion.

Response: We thank the reviewer for this helpful suggestion. We agree that the level of numerical detail regarding cumulative loading doses, while informative, may interrupt the narrative flow of the Discussion. Accordingly, we have revised the manuscript by relocating the detailed loading-dose totals and cumulative dosing calculations to a dedicated supplementary table, while retaining only the key conceptual elements in the Discussion. This revision preserves transparency and reproducibility of the protocol while improving readability and focus in the main text.

1. The safety interpretation is generally balanced, though the assertion that efficacy “surpassed significantly any previously reported replacement method” may be too strong without a formal comparative framework or systematic review.

Response: Thank you for pointing this out. We changed “any” to “many”.

CONCLUSIONS

1. The conclusion effectively reiterates the global burden of vitamin D deficiency; however, the opening sentence could be strengthened by more precisely linking prevalence to the unmet need for practical, scalable treatment strategies.

Response: Thank you for the excellent remark. We made a change in the opening sentence of the Conclusions section in lines 503-504: “but an unmet need for practical, scalable treatment strategies, able to restoring adequacy in the majority of patients are lagging”.

1. The statement that the protocol “appears promising” is appropriately cautious. Yet, the conclusion would benefit from explicitly restating that the evidence derives from a retrospective, real-world analysis, to avoid overgeneralization.

Response: Thank you for the suggestion. We added that in lines 506-507: “yet the data arise from a retrospective real-world analysis”.

1. Consider briefly emphasizing the key strengths of the protocol—such as simplicity, treat-to-target design, and long-term follow-up—while maintaining restraint in claims regarding efficacy and safety.

Response: Thank you for the suggestion. Done as proposed in lines 504-505: “The present is a simple, treat-to-target protocol with long-term follow-up, and appears promising”.

1. The call for future research is appropriate; specifying the need for prospective randomized or parallel-arm comparative studies, and ideally including clinically meaningful endpoints beyond biochemical adequacy, would further strengthen this closing section.

Response: Excellent remark. Done as proposed in lines 507-509: “Further prospective randomized – or with parallel arms studies aiming not only to restore adequacy, but assess the effect on clinically-meaningful outcomes are needed to further evaluate this strategy.”

Thank you again for the opportunity to review this work. The study addresses a significant gap in long-term vitamin D management and, with some refinement in clarity and framing, has the potential to make a meaningful contribution to the field.

Round 2

Reviewer 2 Report

Comments and Suggestions for Authors

The scope of work in this manuscript is too limited. Restoration of blood vitamin D levels to physiological levels can be achieved easily through gradual dose escalation and close monitoring of 25(OH)D levels, without a fixed protocol, because different individuals may respond differently to vitamin D supplementation. It is necessary to see whether such a protocol is necessary for the treatment of certain diseases.

Author Response

Thank you for the constructive feedback. We agree that vitamin D deficiency can be treated using multiple strategies. However, the efficacy of most of these approaches has not been systematically evaluated or published.

At our institution, we have followed a specific treatment strategy consistently over several years. In this study, we evaluated its efficacy and safety in a large population over an extended period. This approach offers several unique perspectives that may be of value to the readership of Nutrients, as it employs a treat-to-target strategy, demonstrates high efficacy, and achieves these outcomes without an increased risk of adverse events or the need for multiple vitamin D measurements.

We believe that all strategies used in clinical practice warrant similar evaluation, and that publication of such findings could help inform physicians on how to address this important clinical issue more effectively.