{ "schema_version": "chamgap-public-criteria-1.0", "verdict_number": "1585", "title": "Vitamin C × HbA1c in type 2 diabetes", "criteria_version": "1.1", "criteria_date": "2026-10-04", "condition_origin": "Chamgap's own application conditions and proposals", "requirements": [ { "item_id": "N01", "question_type": "Efficacy and target population", "question": "Which population with type 2 diabetes does the effect apply to?", "needed": "Obtain trial-specific diagnoses, ages, baseline HbA1c, disease duration, care settings and inclusion/exclusion criteria", "role": "Required", "role_reason": "The broad label 'type 2 diabetes' does not establish that the target populations are equivalent.", "application_exception": "For mixed populations, separate results or documentation of the population mix and indirectness are acceptable. Other types of diabetes require a separate question.", "criterion": "Identify each trial's population, diagnoses and baseline characteristics, and explain matches or differences with the selected claim using locations in the original paper", "basis": "M03 §3.2.1", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Prespecified stratified comparative trials including populations with different representativeness; first obtain tables of the included trials' characteristics" }, { "item_id": "N02", "question_type": "Ingredient, formulation and route", "question": "What was actually administered?", "needed": "Verify the chemical form of vitamin C, single ingredient versus combination, tablet versus capsule, oral route, product and content", "role": "Required", "role_reason": "Needed to avoid attributing effects from other formulations, routes or added ingredients to oral vitamin C.", "application_exception": "Combination products may contribute if shared ingredients and between-group differences can be separated. Intravenous preparations and foods require separate comparisons.", "criterion": "Verify each trial's actual ingredients, route, formulation and control ingredients, while retaining unverified details as unverified", "basis": "M03 §3.2.2–3.2.3", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Obtain product analyses and manufacturing/content records; superiority of a particular formulation requires a direct comparative trial" }, { "item_id": "N03", "question_type": "Dose and exposure", "question": "Which dose is the efficacy question about?", "needed": "Distinguish daily prescribed dose, dosing frequency, actual intake, adherence, baseline diet and vitamin C status", "role": "Required", "role_reason": "If nominal dose differs from actual exposure, applicability and dose interpretation change.", "application_exception": "When baseline deficiency information is absent, retain studies of the overall effect and leave only deficiency-specific applicability unverified.", "criterion": "Link dose, actual exposure, verification methods and duration for each trial contributing to the HbA1c analysis", "basis": "M03 §3.2.2; M15 §15.2.4", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Comparative trials with prespecified exposure measurement and adherence tracking; effect-modification analyses by baseline status" }, { "item_id": "N04", "question_type": "Comparison", "question": "Lower than what comparator?", "needed": "Specify the actual placebo, no-treatment, usual-care or active comparator and fix the group order used to calculate the effect", "role": "Required", "role_reason": "A different comparator means a different question, even when the numerical result is the same.", "application_exception": "Retain active-comparator results, but present them separately from the main question comparing against no added vitamin C.", "criterion": "Verify each trial's control conditions, group order and rationale for inclusion in the synthesis", "basis": "M03 §3.2.3", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Trials explicitly describing placebo/no added vitamin C and shared treatment, or original descriptions of existing comparators" }, { "item_id": "N05", "question_type": "Concomitant treatment", "question": "Can the contribution of added vitamin C be separated?", "needed": "Verify shared diabetes treatment, medication adjustments, diet, exercise, other supplements and changes in both groups", "role": "Required", "role_reason": "Check whether differences in other treatments contribute to the observed difference.", "application_exception": "Do not require completely identical treatment. If treatment changes, review balance, analysis and alignment with the effect of interest.", "criterion": "Link baseline and follow-up concomitant treatments/changes, between-group differences and how they were handled", "basis": "M03 §3.2.3; M08 §8.2.2–8.2.3", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Add-on treatment trials with prespecified records of shared treatment, adjustment rules and rescue treatment" }, { "item_id": "N06", "question_type": "Efficacy study design", "question": "Can intervention effects be distinguished from chance and confounding?", "needed": "Randomization methods, allocation concealment, baseline balance and result-specific risk-of-bias information from comparative trials", "role": "Required (causal efficacy)", "role_reason": "The label 'randomized' alone does not resolve risk-of-bias concerns.", "application_exception": "Also record and use non-randomized studies as supporting evidence. Judgments must fit parallel, crossover or cluster designs. A formal RoB 2 assessment is outside this review's scope.", "criterion": "Obtain original evidence of the actual design, randomization/concealment and relevant baseline differences, and discuss their effect on results", "basis": "M08 §8.1–8.2.3", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Preregistered comparative trials with appropriate randomization, concealment and result analyses; first obtain the original methods" }, { "item_id": "N07", "question_type": "Effect of interest and analysis", "question": "Is this the effect of assignment or the effect of adhering to treatment?", "needed": "Distinguish ITT/PP, analysis populations, adjustment variables, final values versus changes, and handling of crossover/cluster designs", "role": "Required", "role_reason": "Needed to avoid combining different effects and analyses as if they were the same result.", "application_exception": "Crossover/cluster requirements are marked not applicable or handled separately only after the design is verified.", "criterion": "Verify agreement or differences between the effect of interest, the actual analysis and the effect used in the synthesis", "basis": "M08 §8.2.2; M15 §15.3.1", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Comparative trials or reanalysis materials providing a prespecified analysis plan and necessary correlation, period and cluster information" }, { "item_id": "N08", "question_type": "Missing data", "question": "Who was lost to follow-up?", "needed": "Group-specific numbers allocated, completing follow-up, measured and analysed; reasons for dropout, handling of missing data and sensitivity analyses", "role": "Required", "role_reason": "Review the possibility that missing data changed the observed result.", "application_exception": "Do not use an arbitrary universal dropout-rate threshold. Examine causes of missingness and their relationship to the outcome.", "criterion": "Link outcome- and time-specific denominators, missingness, handling methods and results under different assumptions", "basis": "M08 Table 8.2.a", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Trials tracking dropout causes and follow-up with sensitivity analyses under different assumptions; obtain existing flow diagrams and analysis materials" }, { "item_id": "N09", "question_type": "Measured outcome", "question": "Are the HbA1c measurements comparable?", "needed": "Verify HbA1c assay methods, units, blood-sampling times, assay interference/red-cell limitations and assessor blinding", "role": "Required", "role_reason": "Needed to distinguish measurement differences from actual changes.", "application_exception": "Do not generalize glucose-meter interference to all HbA1c assays. Review each assay method separately.", "criterion": "Verify each trial's HbA1c methods, units, visits and measurement limitations. Distinguish percentage points from relative percentages", "basis": "M08 Table 8.2.a; M03 §3.2.4", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Trials reporting assay methods, interference validation and blood-sampling rules; analytical method comparisons where needed" }, { "item_id": "N10", "question_type": "Duration", "question": "Does the observation period fit the question?", "needed": "Record treatment, measurement and follow-up periods separately, with evidence supporting the time frame used to interpret HbA1c changes", "role": "Required", "role_reason": "Short-term observation and sustained effects are different questions.", "application_exception": "Do not adopt an arbitrary minimum number of weeks. An appropriate duration is undetermined from these materials alone.", "criterion": "Specify the timeline of each contributing trial, the questions that timeline can answer and its limitations", "basis": "M03 §3.2.2–3.2.4", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Trials scheduling visits based on the outcome's time characteristics; official original assay references supporting duration criteria require follow-up checking" }, { "item_id": "N11", "question_type": "Result definition", "question": "Exactly what difference was observed?", "needed": "Link effect estimates, measures, units, group order, confidence intervals, time points, denominators and adjustment to original materials", "role": "Required", "role_reason": "Within-group changes, between-group differences and pooled estimates are different results.", "application_exception": "Retain synthesis summaries as results, while distinguishing them from direct results of original trials.", "criterion": "Make analysis attribution traceable so that distinct results are not mistaken for the same effect", "basis": "M15 §15.3.1–15.3.3", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Obtain original trial result tables/supplements and recheck the original numbers; define the unit of analysis before a new synthesis" }, { "item_id": "N12", "question_type": "Precision and sample size", "question": "What conclusions does the interval allow?", "needed": "Link outcome-specific samples, variance and effect intervals to a justified important difference", "role": "Required", "role_reason": "Study or participant counts alone cannot establish sufficiency, and statistical significance does not establish efficacy.", "application_exception": "If a clinical-importance threshold is absent, leave it undetermined. Do not impose an arbitrary minimum sample or trial count.", "criterion": "Compare the effects the CI excludes or allows—important effects, small effects or no difference—with an evidence-based threshold", "basis": "M15 §15.3.1–15.3.3", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Trials with sample sizes based on important-difference, variance and dropout assumptions; first agree on the threshold and obtain existing variance information" }, { "item_id": "N13", "question_type": "Selective reporting", "question": "Can all prespecified results be examined?", "needed": "Compare registration, protocol and analysis plans with reported HbA1c time points, analyses and reasons for changes", "role": "Required", "role_reason": "Examine whether an analysis was selected because its results were favourable.", "application_exception": "Retain the study's existence and results even if registration is absent or private. Do not turn an unverified status into confirmed selective reporting.", "criterion": "Compare prespecified and reported outcomes, analyses and time points, explaining changes or why comparison is impossible", "basis": "M08 Table 8.2.a; M04 §4.6.3", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Trials publishing preregistration, protocols/SAPs and all results, or retrieval of existing registrations/supplements" }, { "item_id": "N14", "question_type": "Study families", "question": "Do three review papers represent independent replication?", "needed": "Link original trials, registrations, related reports and review inclusion tables into study families, recording overlap", "role": "Required", "role_reason": "The same participants or trial must not be counted more than once.", "application_exception": "Retain unresolved study families under provisional identities. Unique trial and participant counts remain undetermined.", "criterion": "Trace report → original trial → inclusion in each review, and identify matching or unresolved identities", "basis": "M04 §4.6.1–4.6.2", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Obtain included-trial/registration lists and compare duplicates; then conduct independent replication in a different recruited population" }, { "item_id": "N15", "question_type": "Inconsistency and replication", "question": "Are results consistent under different conditions?", "needed": "Record trial-specific opposing, no-difference and positive results, condition differences, heterogeneity and prespecified subgroups", "role": "Required (overall applicability)", "role_reason": "One pooled average does not guarantee results in every population and setting.", "application_exception": "Between-study comparison may be not applicable for a single study family, but NA is not assigned here because study families remain unresolved.", "criterion": "Preserve the distribution of unique trial results, explanations of condition differences/inconsistency and uncertainty", "basis": "M03 §3.2.1; M15 §15.3.1", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Independent multicentre replication under standardized conditions; test prespecified hypotheses about baseline status and dose" }, { "item_id": "N16", "question_type": "Dose question", "question": "Is a higher dose better?", "needed": "Direct dose comparisons, exposure/dose response, and joint observation of benefits and harms", "role": "Additional (required for dose selection)", "role_reason": "Dose differences across trials may be confounded by differences in populations and durations.", "application_exception": "The main HbA1c-change question can be retained without claiming dose superiority.", "criterion": "Dose differences within the same comparison framework, or dose-response evidence explicitly describing confounding limitations", "basis": "M03 §3.2.2; Chamgap's own dose-study design proposal", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Randomized dose comparisons using the same formulation and shared treatment. Determine sample sizes and doses after reviewing the evidence" }, { "item_id": "N17", "question_type": "Persistence", "question": "Does the effect persist long term or after stopping treatment?", "needed": "Verify long-term exposure, post-treatment visits, medication changes and HbA1c trajectories", "role": "Additional (required for persistence claims)", "role_reason": "A change at the end of treatment differs from a sustained effect.", "application_exception": "Do not remove short-term studies as ineligible. Leave persistence separately unverified.", "criterion": "Long-term comparative results with timelines, treatment continuation/discontinuation and loss to follow-up", "basis": "M03 §3.2.2; Chamgap's own persistence-study design proposal", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Comparative trials/follow-up studies with prespecified long-term extensions and post-treatment follow-up. Duration is undetermined" }, { "item_id": "N18", "question_type": "Safety", "question": "What harms were observed in the same population at the same dose?", "needed": "Verify group-specific harm definitions, collection methods, event/person counts, denominators, exposure periods and discontinuations", "role": "Required (harm question)", "role_reason": "Non-reporting cannot be interpreted as zero events or established safety.", "application_exception": "Retain efficacy results even when harms are not reported in an efficacy study. Present safety separately.", "criterion": "Distinguish events in both groups, observation periods, denominators, collection methods and non-reporting", "basis": "M19 §19.1.2–19.2.4", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Obtain comparative trials/safety reports documenting both prespecified harm collection and unanticipated harms" }, { "item_id": "N19", "question_type": "Long-term/rare harms and special populations", "question": "What about harms outside short trials and vulnerable populations?", "needed": "Exposure, comparisons, occurrence and long-term harm data in existing caution groups, including people with kidney disease/stone histories or iron overload", "role": "Required (applicable harm assessment)", "role_reason": "The restricted populations and durations of efficacy trials may not capture rare harms.", "application_exception": "Also preserve observational studies, registries and case signals. Without control of confounding and denominators, do not establish incidence rates or causality.", "criterion": "Verify design-specific event definitions, exposure, comparisons/confounding, denominators, durations and population-applicability limitations", "basis": "M19 §19.1.2, §19.2.2–19.2.4", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Long-term cohorts/registries with denominators, exposure and appropriate comparators; special-population data require separate searching" }, { "item_id": "N20", "question_type": "Applicability to subgroups", "question": "Is the effect greater in deficient participants or particular populations?", "needed": "Baseline vitamin C, HbA1c, medication/disease characteristics, prespecified effect-modification hypotheses and interactions", "role": "Additional (required for subgroup claims)", "role_reason": "Needed to avoid extending an overall average to a particular population.", "application_exception": "Pregnancy, children and other types of diabetes are not automatic extensions of this claim.", "criterion": "Verify prespecified hypotheses and definitions, subgroup samples/estimates, interactions and precision", "basis": "M03 §3.2.1; Chamgap's own effect-modification proposal", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Prespecified stratified trials or agreed individual-participant-data analyses. Label subgroups not defined in advance as exploratory" }, { "item_id": "N21", "question_type": "Search, access and publication status", "question": "What might the current record have missed?", "needed": "Search scope/dates, inclusion/exclusion, registrations/unpublished studies, corrections/retractions, and material-specific access/reading histories", "role": "Required (claims about the current overall evidence)", "role_reason": "The existence of a stored summary does not mean the entire current literature has been checked.", "application_exception": "No new clinical search was performed. Only the currently preserved scope applies.", "criterion": "Record the scope in which evidence is absent or unverified, by date and material type", "basis": "M04 §4.5, §4.6.3", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "In an authorized follow-up, search and select new literature/registrations/publication-status information and record access. This was not performed here" }, { "item_id": "N22", "question_type": "Clinical outcomes and scope boundaries", "question": "Does a change in HbA1c directly establish benefits for complications?", "needed": "Questions about complications, quality of life or mortality require separate comparative results, events and durations for those outcomes", "role": "Additional (required for extended claims)", "role_reason": "A boundary distinguishing questions about biomarkers from questions about clinical events.", "application_exception": "Do not require clinical-event trials as a mandatory condition for the selected question about numerical HbA1c change itself.", "criterion": "Identify the separate clinical question/outcome and direct evidence. Do not automatically extend HbA1c findings", "basis": "M03 §3.2.4; Chamgap's own boundary for extended claims", "condition_origin": "Chamgap's own application conditions and proposals", "proposed_research": "Long-term comparative trials based on clinical events, with a separately defined question. This is not a new claim or search in this case" } ], "method_sources": [ { "id": "M03", "version": "Cochrane Handbook 6.5 (2024), chapter updated 2023-08", "url": "https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-03", "section": "§3.1, §3.2.1–3.2.3, MECIR C5/C7/C13", "official_principle": "Clearly record the question, eligibility conditions and reasons for changes, and distinguish variations of the intervention.", "review_level": "Relevant sections of the original web text reviewed directly; not an application of the chapter's entire methodology" }, { "id": "M04", "version": "Cochrane Handbook 6.5.1 (2025), chapter updated 2025-03", "url": "https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-04", "section": "§4.5, §4.6.1–4.6.3, MECIR C42", "official_principle": "Distinguish and link studies and reports; do not omit a study solely because an outcome is unreported.", "review_level": "Relevant sections of the original web text reviewed directly; not an application of the chapter's entire methodology" }, { "id": "M08", "version": "Cochrane Handbook 6.5 (2024), chapter updated 2019-10", "url": "https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-08", "section": "§8.1–8.2.3, Table 8.2.a", "official_principle": "Define the result and effect of interest before examining randomization, deviations, missing data, measurement and selective reporting.", "review_level": "Relevant sections of the original web text reviewed directly; not an application of the chapter's entire methodology" }, { "id": "M15", "version": "Cochrane Handbook 6.5 (2024), chapter updated 2023-08", "url": "https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-15", "section": "§15.2.4, §15.3.1–15.3.3", "official_principle": "Distinguish effect estimates, intervals, importance and applicability. Sample size alone does not determine precision.", "review_level": "Relevant sections of the original web text reviewed directly; not an application of the chapter's entire methodology" }, { "id": "M19", "version": "Cochrane Handbook 6.5 (2024), chapter updated 2019-10", "url": "https://www.cochrane.org/authors/handbooks-and-manuals/handbook/current/chapter-19", "section": "§19.1.2, §19.2.1–19.2.4", "official_principle": "Harm questions may require different designs, populations and follow-up than efficacy questions. Case reports do not establish incidence rates.", "review_level": "Relevant sections of the original web text reviewed directly; not an application of the chapter's entire methodology" } ], "status_dictionary": { "Partly verified": "Some required conditions were verified in the stored summary. This does not mean all conditions were met", "Unverified": "Required information/conditions could not be established within this review's scope", "Review incomplete": "Original-material comparisons/searches within the permitted scope were not performed", "Not reported": "A scope-limited status meaning that the item was not stated in the particular material/section that was read", "Inaccessible": "Used only when access was actually attempted and failed. Not assigned to the clinical materials in this review", "Insufficient evidence for the conditions": "Used only after relevant studies within a defined scope have been reviewed and evidence answering the conditions is insufficient. Not applied across the board in this review", "Not applicable": "A specific exception based on applicability conditions. Not a replacement status for unread materials", "Conflicting data": "Used when compared data for the same question, time point and analysis are difficult to reconcile. Not assigned merely because review estimates differ", "Met": "All required conditions can be explained using locations in original sources. Not synonymous with established efficacy" }, "language": "en", "translation_date": "2026-10-09" }