This study investigated the association between coffee drinking timing patterns and mortality risk using data from the NHANES, WLVS, and MLVS. Two distinct patterns were identified: "morning-type" (36% of participants), characterized by coffee consumption concentrated in the morning, and "all-day-type" (16%), with consumption spread throughout the day. The morning-type pattern was significantly associated with a lower risk of all-cause mortality (HR: 0.88; 95% CI: 0.81-0.96) and CVD-specific mortality (HR: 0.69; 95% CI: 0.55-0.87) compared to non-coffee drinking. The all-day-type pattern did not show a significant association with mortality risk. A significant interaction was found between coffee drinking timing and coffee intake amounts for all-cause mortality (P-interaction = 0.031), with moderate to heavy consumption associated with lower risk only among morning-type drinkers.
This study provides compelling evidence for an association between coffee drinking timing and mortality risk, suggesting that a morning-type pattern is associated with lower all-cause and CVD-specific mortality. The use of robust statistical methods and multiple datasets strengthens these findings. However, the observational nature of the study precludes causal inferences, and the observed associations could be influenced by unmeasured confounding factors or reverse causation.
The practical utility of these findings lies in their potential to inform public health recommendations regarding coffee consumption. The study suggests that concentrating coffee intake in the morning may be more beneficial than consuming it throughout the day. This aligns with the growing body of research on chrononutrition, which emphasizes the importance of meal timing in optimizing health outcomes. However, it is important to note that these findings are specific to the US population and may not be generalizable to other populations with different coffee consumption habits and cultural contexts.
While this study provides valuable insights, it is crucial to acknowledge the uncertainties that remain. The precise mechanisms underlying the observed associations are not fully understood, although circadian rhythm disruption and the anti-inflammatory effects of coffee are proposed as potential explanations. Further research is needed to confirm these mechanisms and to explore the potential role of other factors, such as genetics and lifestyle, in modifying the relationship between coffee drinking timing and mortality.
A critical unanswered question is whether the observed associations are truly causal. Future research should employ study designs that can establish causality, such as randomized controlled trials or Mendelian randomization studies. Additionally, the long-term effects of different coffee drinking timing patterns on various health outcomes, beyond mortality, need to be investigated. While the methodological limitations, such as the reliance on self-reported data and the potential for residual confounding, are acknowledged, they do not fundamentally undermine the study's conclusions. However, they do highlight the need for cautious interpretation and further research to validate these findings.
The Introduction effectively establishes the context of the research by highlighting the global popularity of coffee and its potential health implications.
The section logically progresses from general coffee consumption to the specific research focus on timing, building a clear rationale for the study.
The Introduction clearly identifies the research gap by stating that the impact of coffee drinking timing on health outcomes is not well understood.
This medium-impact improvement would enhance the reader's understanding of the study's theoretical underpinnings. The Introduction section is the appropriate place to introduce this concept as it provides the foundation for the research question regarding coffee drinking timing. Expanding on the concept of circadian rhythm would strengthen the paper by providing a more comprehensive background for readers unfamiliar with this area. This would also help to emphasize the novelty and significance of investigating the role of timing in coffee consumption's health effects. Ultimately, providing a more detailed explanation of circadian rhythm would improve the study's scientific contribution by ensuring that the research question is properly contextualized and its importance is fully appreciated.
Implementation: 1. Briefly define circadian rhythm and its role in regulating physiological processes. 2. Provide examples of how disruption of circadian rhythm can impact health. 3. Explain how coffee consumption, particularly the timing, might interact with circadian rhythm.
This medium-impact improvement would further solidify the justification for the study's focus. While the Introduction mentions the potential for coffee timing to modify health outcomes, it could more explicitly connect this to the broader implications for public health and personalized nutrition. This belongs in the Introduction as it reinforces the motivation behind the research. Strengthening the rationale would enhance the paper by highlighting the potential impact of the findings on dietary recommendations and public health guidelines related to coffee consumption. This would also underscore the study's contribution to the growing field of chrononutrition. Ultimately, a more compelling rationale would increase the study's significance by emphasizing the practical implications of understanding the role of coffee drinking timing in health outcomes.
Implementation: 1. Briefly discuss the potential public health implications of understanding how coffee timing affects health. 2. Mention the possibility of personalized dietary recommendations based on coffee drinking patterns. 3. Connect the research to the broader field of chrononutrition.
This low-impact improvement would enhance the clarity and precision of the Introduction. While the section mentions "heavy coffee consumption," providing a more precise definition early on would benefit readers. This is appropriate for the Introduction as it sets the context for the research. Clarifying the definition would improve the paper by ensuring consistency and avoiding ambiguity throughout the study. This would also facilitate comparisons with other research on coffee consumption. Ultimately, a clear definition of heavy consumption would enhance the study's methodological rigor by ensuring that the research question is clearly defined.
Implementation: 1. Provide a specific range for heavy coffee consumption (e.g., "more than 4 cups per day"). 2. Briefly explain the rationale for this definition, if applicable.
The study utilizes multiple large, well-established datasets, including NHANES, WLVS, and MLVS, which enhances the generalizability and validity of the findings.
The use of 24-hour dietary recalls in NHANES and 7-day dietary records in WLVS and MLVS provides detailed information on the timing and amount of coffee consumption.
The application of two-step cluster analysis and Cox proportional hazards models demonstrates a rigorous statistical approach to identifying patterns and assessing associations.
The study includes multiple sensitivity analyses and external validation using different datasets, which strengthens the robustness of the findings.
This medium-impact improvement would enhance the methodological transparency of the study. The Methods section is the appropriate place to provide this justification as it directly relates to how the key exposure variable is defined. Providing a clear rationale for the chosen time periods would strengthen the paper by ensuring that the categorization is not perceived as arbitrary and by demonstrating that it is based on sound scientific reasoning or prior evidence. This would also allow readers to better evaluate the appropriateness of the categorization and its potential impact on the study's findings. Ultimately, clarifying the rationale for the time period categorization would improve the study's methodological rigor by providing a more transparent and well-justified approach to defining coffee drinking timing.
Implementation: 1. Briefly explain the rationale for choosing the specific time periods (morning, afternoon, evening). 2. Cite any relevant literature or prior research that supports this categorization. 3. If the categorization is based on physiological considerations (e.g., circadian rhythm), briefly explain the connection.
This medium-impact improvement would enhance the reproducibility and transparency of the study. The Methods section is the ideal location for this information as it pertains to the core statistical technique used to identify coffee drinking patterns. Providing more details about the cluster analysis parameters would strengthen the paper by allowing other researchers to fully understand and potentially replicate the analysis. This would also enable readers to better assess the validity of the identified clusters and their robustness to different parameter choices. Ultimately, elaborating on the cluster analysis parameters would improve the study's methodological rigor by ensuring that the pattern identification process is transparent, reproducible, and well-justified.
Implementation: 1. Specify the exact criteria used for pre-clustering. 2. Describe in more detail how the silhouette width method was applied to determine the optimal number of clusters. 3. Provide the specific log-likelihood distance measure used. 4. Explain any other relevant parameter settings or choices made during the cluster analysis.
This low-impact improvement would enhance the study's robustness by acknowledging and addressing a potential limitation. The Methods section is the appropriate place to discuss this as it relates to the measurement of the primary exposure variable. Acknowledging the potential for misclassification due to reliance on self-reported data would strengthen the paper by demonstrating a critical awareness of the limitations inherent in dietary recall methods. Discussing how this potential misclassification might affect the results would further enhance the study's transparency and allow readers to interpret the findings with appropriate caution. Ultimately, addressing the potential for misclassification of coffee timing would improve the study's scientific rigor by acknowledging and mitigating a potential source of bias.
Implementation: 1. Briefly acknowledge that self-reported dietary data may be subject to recall bias, potentially leading to misclassification of coffee drinking timing. 2. Discuss the potential direction and magnitude of this bias. 3. Suggest ways in which future studies could minimize this bias (e.g., using more objective measures of coffee consumption or timing).
The Results section clearly presents the identified coffee drinking patterns and their associations with mortality, supported by specific hazard ratios and confidence intervals.
The study employs robust statistical methods, including Cox proportional hazards models and interaction analyses, to assess the relationship between coffee drinking patterns and mortality.
The researchers conducted multiple sensitivity analyses and validated their findings using different datasets and approaches, strengthening the credibility of the results.
This medium-impact improvement would enhance the reader's understanding of the identified clusters. The Results section is the appropriate place for this contextualization as it directly relates to the characteristics of the groups being compared in the subsequent analyses. Providing more context for the cluster characteristics would strengthen the paper by allowing readers to better interpret the observed associations between coffee drinking patterns and mortality. This would also help to identify potential confounding factors or effect modifiers that might be related to the differences between the clusters. Ultimately, providing more context for the cluster characteristics would improve the study's scientific contribution by ensuring that the findings are properly interpreted and their implications are fully understood.
Implementation: 1. Briefly describe the demographic, lifestyle, and health characteristics that most strongly differentiate the morning-type and all-day-type clusters. 2. Discuss any notable differences in these characteristics between the two clusters. 3. Consider adding a supplementary table that provides a more detailed comparison of the cluster characteristics.
This medium-impact improvement would provide a more nuanced interpretation of the study's results. The Results section is the appropriate place to discuss the implications of null findings as it is where the results are presented and interpreted. Elaborating on the implications of the null findings would strengthen the paper by providing a more balanced and comprehensive discussion of the results. This would also help to guide future research by highlighting areas where further investigation is needed. Ultimately, elaborating on the implications of the null findings would improve the study's scientific contribution by ensuring that all results, both positive and negative, are given appropriate consideration.
Implementation: 1. Briefly discuss the implications of the lack of association between the all-day-type pattern and mortality risk. 2. Consider potential explanations for this null finding. 3. Discuss whether this finding aligns with or contradicts previous research.
This low-impact improvement would enhance the transparency of the study's methodology. The Results section is the appropriate place to briefly mention this rationale, as it directly relates to the statistical models used to analyze the data. Clarifying the rationale for choosing specific covariates would strengthen the paper by demonstrating that the selection was based on sound scientific reasoning and prior research. This would also allow readers to better evaluate the appropriateness of the statistical models and the potential for residual confounding. Ultimately, clarifying the rationale for covariate selection would improve the study's methodological rigor by providing a more transparent and well-justified approach to the statistical analysis.
Implementation: 1. Briefly explain why the chosen covariates were included in the statistical models. 2. Cite any relevant literature or prior research that supports the inclusion of these covariates. 3. If certain covariates were chosen based on their potential to confound the association between coffee drinking timing and mortality, briefly explain the hypothesized confounding mechanism.
Figure 1 Distribution and characteristics of study participants. (A) Distribution of participants according to two-step clustering for the total population in the National Health and Nutrition Examination Survey. (B) Distribution of participants provided the first-day dietary data in the National Health and Nutrition Examination Survey. (C) Distribution of participants provided the second-day dietary data in the National Health and Nutrition Examination Survey. (D) Distribution of participants according to two-step clustering in Women's Lifestyle Validation Study. (E) Distribution of participants according to two-step clustering in Women's Lifestyle Validation Study. Morning was defined as from 4 a.m. to 11:59 a.m., afternoon from 12 p.m. to 4:59 p.m., and evening from 5 p.m. to 3:59 a.m. NHANES, National Health and Nutrition Examination Survey; WLVS, Women's Lifestyle Validation Study; MLVS, Momen's Lifestyle Validation Study
Table 1 Characteristics of participants by patterns of coffee drinking timing in National Health and Nutrition Examination Survey
Table 2 Association of coffee drinking timing with mortality in National Health and Nutrition Examination Survey
The Discussion effectively highlights the novel contribution of the study, emphasizing that it is the first to investigate the association between patterns of coffee drinking timing and mortality risk.
The authors effectively articulate the main findings of the study, particularly the identification of two distinct coffee drinking patterns (morning-type and all-day-type) and their differential associations with mortality risk. The explanation is clear and concise, making it easy for readers to grasp the key results.
The Discussion provides plausible biological mechanisms to explain the observed associations, focusing on circadian rhythm disruption and the anti-inflammatory effects of coffee.
This medium-impact improvement would provide a more comprehensive and balanced discussion of the study's findings. While the Discussion section mentions potential mechanisms, it could benefit from exploring alternative explanations for the observed associations. This belongs in the Discussion as it is where the results are interpreted and their implications are considered. Expanding on alternative explanations would strengthen the paper by demonstrating a more critical and thorough consideration of the findings. This would also help to identify potential areas for future research and ensure that the study's conclusions are not overstated. Ultimately, exploring alternative explanations would improve the study's scientific rigor by providing a more nuanced and comprehensive interpretation of the results.
Implementation: 1. Discuss the possibility that the morning-type pattern is a marker for other healthy lifestyle factors not fully accounted for by the adjustments. 2. Explore the potential role of unmeasured confounders related to socioeconomic status, stress levels, or other factors that might influence both coffee drinking timing and mortality risk. 3. Consider the possibility that the observed associations are due to reverse causation, where individuals with certain health conditions might alter their coffee drinking habits.
This high-impact improvement would enhance the transparency and credibility of the study. While the Discussion acknowledges some limitations, it could benefit from a more in-depth discussion of their potential impact on the findings. This is crucial in the Discussion section as it provides the context for interpreting the results and assessing their validity. Strengthening the discussion of limitations would enhance the paper by demonstrating a more critical awareness of the study's shortcomings and their potential implications. This would also help readers to better evaluate the strength of the evidence and the generalizability of the findings. Ultimately, a more thorough discussion of limitations would improve the study's scientific rigor by providing a more balanced and transparent assessment of the research.
Implementation: 1. Elaborate on the potential for recall bias and measurement error due to the reliance on self-reported dietary data, and discuss how this might have affected the results. 2. Discuss in more detail the potential for residual confounding, even after adjusting for a wide range of covariates. 3. Explicitly address the limitation that the study population was restricted to US adults, and discuss the implications for generalizability to other populations. 4. Acknowledge the lack of data on other factors that might influence coffee drinking timing, such as shift work or chronotype.
This medium-impact improvement would enhance the study's contribution to the field by providing a clearer roadmap for future investigations. The Discussion section is the appropriate place for this as it is where the implications of the findings are considered and future directions are proposed. Providing more specific recommendations for future research would strengthen the paper by guiding researchers in building upon the current study's findings. This would also help to address the limitations of the present study and advance the understanding of the relationship between coffee drinking timing and health outcomes. Ultimately, more specific recommendations for future research would improve the study's impact by facilitating further investigation and contributing to the development of evidence-based dietary guidelines.
Implementation: 1. Suggest specific research designs that could help to establish causality, such as randomized controlled trials or Mendelian randomization studies. 2. Recommend specific areas for future research to explore the underlying mechanisms, such as studies investigating the effects of coffee timing on circadian biomarkers or inflammatory markers. 3. Propose research to examine the association between coffee drinking timing and mortality risk in diverse populations, including different age groups, ethnicities, and countries. 4. Suggest studies that investigate the potential interaction between coffee drinking timing and other lifestyle factors, such as diet, exercise, and sleep patterns.
Figure 2 Joint association between coffee intake amounts and coffee drinking timing on the risk of mortality. One cup equal to 8 ounces (1 ounce 28.3 g); models adjusted for age, sex, race, and ethnicity, National Health and Nutrition Examination Survey cycles, family income, education levels, body mass index, diabetes, hypertension, high cholesterol, smoking status, time of smoking cessation, physical activity, Alternative Healthy Eating Index, total calorie intake, tea intake, caffeinated soda intake, percentage of decaf intake, short sleep duration, and trouble sleeping. HR, hazard ratio; CI, confidential interval; CVD, cardiovascular disease
Figure 3 Dose-response relationships between coffee intake amounts and the risk of mortality according to patterns of coffee drinking timing. Models adjusted for age, sex, race, and ethnicity, National Health and Nutrition Examination Survey cycles, family income, education levels, body mass index, diabetes, hypertension, high cholesterol, smoking status, time of smoking cessation, physical activity, Alternative Healthy Eating Index, total calorie intake, tea intake, caffeinated soda intake, percentage of decaf intake, short sleep duration, and trouble sleeping. HR, hazard ratio; CI, confidential interval; CVD, cardiovascular disease
The Conclusions section effectively summarizes the key findings, highlighting the association between coffee drinking timing and mortality risk.
The section clearly states the main implication of the study, emphasizing the importance of considering drinking timing in the association between coffee intake and health outcomes.
The authors appropriately acknowledge the limitations of the study, including its observational nature and the potential for confounding.
This medium-impact improvement would enhance the real-world relevance of the study. The Conclusions section is the ideal place for this discussion as it is where the overall significance of the findings is presented. Expanding on the practical implications would strengthen the paper by bridging the gap between research findings and their potential application in public health and individual behavior. This would also help readers understand the broader context of the study and its potential impact on dietary recommendations. Ultimately, discussing the practical implications would enhance the study's impact by highlighting its relevance beyond the academic realm.
Implementation: 1. Briefly discuss the potential implications of the findings for public health recommendations regarding coffee consumption. 2. Suggest how individuals might consider adjusting their coffee drinking habits based on the study's results. 3. Mention the potential for personalized dietary advice based on coffee drinking patterns.
This medium-impact improvement would enhance the cohesiveness of the paper and reinforce the study's key message. The Conclusions section is where the findings are synthesized and their broader significance is discussed, making it the appropriate place to explicitly connect back to previous sections. Strengthening the connection to previous sections would enhance the paper by providing a more integrated and holistic view of the research. This would also help readers to better understand how the different parts of the study fit together and contribute to the overall conclusions. Ultimately, explicitly linking the conclusions to previous sections would improve the paper's narrative flow and reinforce the study's main findings.
Implementation: 1. Briefly reiterate how the findings build upon the research gap identified in the Introduction. 2. Mention how the Results and Discussion sections support the conclusions drawn. 3. Briefly summarize how the identified mechanisms in the Discussion relate to the observed associations in the Conclusions.
This low-impact improvement would further emphasize the study's unique contribution to the field. The conclusion section is the appropriate place to do this as it provides the final takeaway message for the reader. Reiterate novelty and contribution more forcefully would enhance the paper by solidifying the study's significance and its impact on the existing literature. This would also help to position the research within the broader scientific context and highlight its value to the field. Ultimately, more forcefully emphasizing the study's novelty and contribution would improve the paper's impact by leaving a stronger impression on the reader and underscoring the study's importance.
Implementation: 1. Restate that this is the first study to examine the association between coffee drinking timing patterns and mortality risk. 2. Briefly highlight the unique methodological approach used. 3. Emphasize the potential of the findings to advance the understanding of the relationship between coffee consumption and health.