PONE-D-25-11838Midlife and old-age cardiovascular risk factors, educational attainment, and cognition at 90-years – population-based study with 48-years of follow-upPLOS ONE

Dear Dr. Varjonen,

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Additional Editor Comments:

This could potentially be suitable for publication in PLOS One, but will require substantial revision and some additional analyses.

In addition to addressing comments and concerns raised by the reviewers, please address my comments below.

The research questions and analytic plan do not appear to have been pre-registered (e.g. Open Science Framework or similar). Given the number of statistical tests, this increases the likelihood of chance and unstable findings.

Is there anywhere else the questions and plan were stated in advance (e.g. data sharing applications, ethics forms)? Include if possible.

There is no mention of childhood intelligence yet a substantial literature on the long-reaching consequences. Educational attainment is not the same thing, particularly for older cohorts and older women, whose years of education would be influenced by sociological factors not just childhood intelligence. At the very least, please acknolwedge this literature and the limitation that you were not able to consider this in your analysis.

I was suprising not to see use of inverse probability weights to address non-random attrition and drop-out (and reduce bias). You could upweight participants similar to non-responders and dropouts, to reduce possible bias (or at least evaluate differences vs. unweighted analysis). This is fairly common an approach.

Please construct a composite of global/general function - all three tests, for comparison. I would have done global function as the main analysis, then specific tests as secondary or even supplementary/exploratory analysis.

The role of healthy survivor effects and very small sample size (low statistical power) are mentioned only briefly but are fundamental limitations. Much more emphasis and reflection on this is needed, particularly in the discussion section.

Healthy survivor effects could create spurious and associations in the opposite direction to the causal effects.

P2 ABSTRACT. Is "Cardiovascular Risk Factors, Aging, and Dementia (CAIDE)" and "dementia risk factors" the same thing? Reword for clarity to avoid confusion.

P2L36 Do you mean cognitive aging or aging?

P2L40 "substantial proportion" and "high prevalence" reads akwardly. Can you report prevalence for both with the same term?

P3L54 "midlife and old age" is confusing - state age range more simply. Then there can be no doubt about the meaning of each term.

P3L56 It reads strangely that you are using "previously validated" dementia risk scores yet your question concerns their validity in a population they were not validated for. If the aim of the study is to validate them on an older age, be more clear about this. If the assumption is made that using risk scores validated at midlife will suffice on old age adults, that sounds quite weak, so needs rewriting for clarity and strength.

P3L58 Hypothesized - but not pre-registered anywhere?

P3L61 Missing statement "..have a reversed association with cognition ON THE BASIS THAT...."

P3L65 I do not understand this: "irrespective of co-twin's vital status or participation". Do you mean any surviving twin was eligible? Please use the STROBE language (eligible, recruited, analysed etc.) and add flow diagram.

P4 The NONAGINTA term suddenly appears from nowhere and is quite jarring. It needs a brief introduction and rewording e.g. to make it clear that this is a nested/sub study of a larger cohort.

P4L73 Why is the 1990 cohort so much smaller than the others?

P4L81 Here and elsewhere, please use age range observed and year(s) observed. Readers not involved in the study need to quickly understand how old and when data were collected.

P4L89 Be careful creating binary variables, you lose variation and results are more likely to drift to null. See commentary on dichotomania (https://www.fharrell.com/post/errmed/)

P5L92 Language - "had used" not "have used". "none in 1981" not "while none in 1981"

P5L95 If you must used binary variables, simpler here to say normal/low and high rather than "One person...."

P5L103 Why frequency of alcohol use but not quantity or hazardous pattern?

P5L107 Careful with the term "this study" which can be confusing when writing up specific questions in samples nested in wider cohorts. Some readers will get confused about what "study" this refers to, particularly if you have just mentioned three sets of questionnaires over many years. Consider "For our analysis" or similar.

P6L114 I don't understand this: "as opposed to original CAIDE with in-person measurements" and so might not readers.

P6L113 I appreciate the need to reference previously published cut-points [8, 12, 8] but can you briefly state some additional information so that we don't have to look up and read these papers separately? It's a bit too brief currently.

P6L145 I appreciate the drop-out analysis, but many readers (including me) are more familiar with inverse probability weighting to evaluate drop-out bias i.e. logistic regression of drop-out and end of follow-up based on socio-demographic and other predictors at baseline, save probability, take inverse, use inverse to upweight responders who look most similar to dropouts. Compare results side by side - materially different?

P6L153 Returning a questionnaire is widely considered to represent informed consent, particulalry in an existing study where participants are used to completing them. Why would that differ today - can you briefly explain (I wasn't sure why newer legislation needs to be mentioned if it was ethical and legal).

P8 Table 1 - Why the sudden drop in 1990 to N = 53 (see earlier point - inclusion criteria at this phase not clear, needs STROBE detail). Why APOE-e4 different proportions for men/women?

P9L179 Healthy survivor effects - very few smokers remained at older ages.

P12L257 The drop-out analysis is informative but descriptive - it is does not evaluate the impact of bias on substantive results, whereas IPW might to some extent.

P12L267 Nothing mentioned on childhood IQ which could drive CVD risk, cognitive aging, dementia risk across the lifecourse. Studies should be cited on this missing antecedent variable.

P13L277 Be clearer here - are you saying hypertension and higher BMI were associated with better cognitive function (cross-sectionally), less cognitive decline. Longitudinally? Were these impacted potentially by reverse causaal, healthy survivor, dropout effects? Are there any administrative data / whole population studies which can clarify or compare?

P13L282 Suggest "participants" not "people" here.

P13L283 Rewrite for clarity: "...is one of the most prevalent dementia risk factors, with nearly 60% increased risk...". I do not understand this sentence. Do you mean being hypertensive at midlife is the most commonly ocurring risk factor, and that aditionally it increases relative risk by 60%, or 60% of dementia is attributable to hypertension at midlife, or something else? Rewrite so that it cannot be misunderstood.

P14L294 This section feels a little rushed e.g. "should be considered when interpreting results". Why? Be specific. Lean into your main limitations - low statistical power, healthy survivor effects, multiple testing, lots of predictors, lots of heterogeneity. Position these with clear next steps for future researchers to design precise research questions and better study designs.

P14L300 This one sentence on 'selected group' understates the problem - it could be a whole paragraph in my view. Also - IPW might fundamentally offer different and more interesting results, even if to show how different the results are when explicitly modelling dropout characteristics using weights.

P14L305 Careful here - you are making policy statements (access to education) but childhood IQ was not measured. In older cohorts, number of years of education would be correlated with childhood IQ but societal factors might drive number of years, particularly for women. You cannot disentangle childhood intelligence from educational attainment easily (and not at all in this dataset), so you should not be making statements about educational policy and resource allocation. Reword as possible mechanisms for future study in longitudinal (ideally life course longitudinal) studies. Also, given low power, you should make the suggestions that studies from several populations should be pooled together, to improve power and study heterogeneity of effects (e.g. individual participant meta-analysis).

Figure 1. This needs redesigning slightly - the arrows were confusing me. NONAGINTA was created in 2020/23 but the arrows moving to the right refer to it from 1975 onwards, higher up. Please design so that it is clearer at first glance, that NONAGINTA is nested within a wider cohort. See STROBE guidelines and flow diagram examples. Again, I wasn't clear why the 1990 cohort was so much smaller - is this by design? What is the reason?

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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: Partly

Reviewer #2: Yes

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2. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #1: N/A

Reviewer #2: Yes

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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

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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

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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: Dear Authors,

Thank you for the opportunity to review your manuscript entitled “Midlife and old-age cardiovascular risk factors, educational attainment, and cognition at 90-years – population-based study with 48-years of follow-up.”

I kindly commend you on an ambitious and important study that uses a rich, population-based twin cohort to investigate the long-term impact of education and cardiovascular health on cognition in the oldest-old. The extensive follow-up and the integration of both midlife and late-life risk factors add considerable value to the field of cognitive aging. Please find below my feedback.

I believe these revisions will substantially strengthen the manuscript. Thank you again for your thoughtful and important contribution to the literature on aging and cognitive health.

With best regards,

The Reviewer

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Major Points

1. Sample Size and Statistical Power

• The final sample size (N = 96) is modest, especially for subgroup comparisons (e.g., BP categories), and likely underpowered for some outcomes such as delayed recall.

• Please comment on the statistical power for the primary outcomes. Consider reporting effect sizes (e.g., Cohen’s d or beta coefficients with 95% CI) consistently throughout to contextualize findings.

2. Reverse Causation and Selection Bias

• The finding that midlife hypertension is associated with better cognitive outcomes is contrary to existing literature and may reflect reverse causality or selection bias.

• Discuss this thoroughly and consider stratified analyses (e.g., by antihypertensive medication use).

• Consider controlling for or reporting on duration of medication use.

• Acknowledge potential survivor bias more explicitly in both the results and discussion.

3. Interpretation of CAIDE Score

• The CAIDE score did not predict cognitive outcomes, despite being a validated dementia risk tool. This discrepancy is insufficiently addressed.

• Discuss potential reasons why CAIDE performed poorly.

• Clarify how CAIDE scores were calculated from self-report.

• Consider additional analyses excluding the education component or including APOE status.

4. Educational-Occupational Score

• This composite measure consistently predicted cognition, outperforming CAIDE.

• Clarify what time period the work-related questions refer to. Discuss the extent to which this score may reflect cognitive reserve, and how it relates to lifelong intellectual engagement.

5. Delayed Recall Floor Effects

• The average delayed recall score (2.2 out of 10) suggests a potential floor effect.

• Consider alternative modeling strategies (e.g., zero-inflated or transformed models).

• Discuss limitations of the telephone-based assessment in very old adults.

Minor Comments

• Abstract: Consider rephrasing “no consistent associations” with more precise language.

• Figure captions: Add sample sizes and clarify whether multiple comparisons were corrected.

• Define what constitutes “high” vs. “normal” BP based on Finnish guidelines in the 1970s–1980s.

• Specify how missing data were handled (e.g., imputation, complete-case analysis).

• Clarify APOE genotyping procedures (e.g., DNA source, platform).

Questions for the Authors

1. Can you elaborate on how education was treated longitudinally—was the highest value used across waves?

2. Could the paradoxical effect of midlife hypertension reflect early treatment or better access to care? Have you considered stratifying analyses based on antihypertensive use?

3. Do you view the educational-occupational score as a proxy for cognitive reserve? If so, how does this fit with the null CAIDE findings?

4. Do attrition analyses suggest meaningful differences in baseline risk factors between completers and non-completers?

5. How might findings generalize to more diverse, less homogeneous populations?

Reviewer #2: This study examined the association between cognitive function and cardiovascular risk factors. 96 participants were followed up for an average of 46 years. High numbers of statistical test were performed and the main result showed that high education was associated with better cognitive functioning at 90 years of age. Some other associations were also found but these remained a bit inconsistent. Interestingly, CAIDE score was not associated with cognitive function.

The long follow-up time is the greatest strength of this study. However, the number of participants is quite low, N=96. This is a significant concern that brings a lot of uncertainty to the interpretation of the results. Low number of participants and high number of statistical tests raises the concern of multiple testing problem.

Furthermore, I have some other comments.

1. What were the shortest and the longest follow-up time?

2. In covariates, blood pressure and total cholesterol were used as binary variables where high and normal levels were evaluated based on self-reported questionnaire. This raises some concerns because, for example, very low blood pressure has been reported to be associated with poor cognitive function or increased dementia risk. The self-reported high or normal levels may increase the risk of bias because the cut-off values for the binary variables are not known at all. It would be clearer to state in the actual manuscript that the covariates are not based on actual measurements.

3. Please address the potential role of multiple testing on the observed associations.

4. There are no details on how many of participants had dementia. How are the risk factors associated with dementia risk?

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Reviewer #1: Yes:  Miray Budak

Reviewer #2: Yes:  Juuso O. Hakala

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Midlife and old-age cardiovascular risk factors, educational attainment, and cognition at 90-years – population-based study with 48-years of follow-up

PONE-D-25-11838R1

Dear Dr. Varjonen,

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.

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Kind regards,

Gareth Hagger-Johnson

Academic Editor

PLOS ONE

Reviewers' comments:

Reviewer's Responses to Questions

Comments to the Author

1. If the authors have adequately addressed your comments raised in a previous round of review and you feel that this manuscript is now acceptable for publication, you may indicate that here to bypass the “Comments to the Author” section, enter your conflict of interest statement in the “Confidential to Editor” section, and submit your "Accept" recommendation.

Reviewer #2: All comments have been addressed

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2. 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 #2: Yes

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3. Has the statistical analysis been performed appropriately and rigorously?

Reviewer #2: Yes

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4. 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 #2: No

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5. 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 #2: Yes

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6. 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 #2: The authors have successfully answered to all my comments. Therefore, I recommend to accept this study for publication.

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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 #2: Yes:  Juuso O. Hakala

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