Hypothesis-Generating Brief: Spermidine supplementation

Hypothesis-Generating Brief: Spermidine supplementation

Abstract

Evidence-honesty note: 35/42 retained sources are coded as null or no extracted directional signal; this corpus is non-supportive for clinical efficacy claims and hypothesis-generating only. Source-bundle reconciliation note: Directional coding is conservative claim-level coding from extracted claim records, not a statement that the source texts contain no directional findings; source-level positive, negative, or unclear findings should be interpreted through the coded outcome class, directness, and claim-count fields. 37/42 retained sources are indirect, review-level, adjacent, or mechanistic and are used only to bound interpretation. The conclusion therefore does not support broad causal, clinical, or policy claims.

This paper synthesizes evidence on Spermidine supplementation across 42 included source papers and 1250 high-confidence extracted claims.

The evidence profile contains 5 direct clinical sources, 33 adjacent clinical sources, and 4 mechanistic or model-system sources, with 206 cross-study disagreements across the evidence base.

Positive study-level signals are summarized in the immune and inflammation outcome class; null signals are summarized in the contextual adjacent evidence, mechanism, dosing and pharmacokinetics, longevity, cardiometabolic, deficiency prevalence, muscle function, and skeletal, fracture, and bone outcome classes; negative signals are not the dominant direction in any outcome class; mixed or heterogeneous signals are summarized in the safety and comorbidity and frailty outcome classes. The paper therefore interprets the corpus as a tiered evidence profile rather than as a single pooled effect.

The conclusion is that Spermidine supplementation should be treated as a bounded geroscience hypothesis: the retained clinical and mechanistic evidence profile defines the scope for targeted testing, while mixed and null findings limit any unqualified anti-aging claim.

Methods

Review type and protocol

This manuscript is reported as a Thin-corpus evidence brief. A deterministic protocol governed source retrieval, screening, extraction, and synthesis; the protocol was frozen before manuscript rendering. The full audit trail is in the supplementary methods_pack.json and the timestamped submission directory synthesis-spermidine-v06-DAILY-2026-06-23T23-09-55Z-R2.

Information sources

Sources were retrieved across PubMed, Europe PMC, OpenAlex, Semantic Scholar, Crossref, DOAJ, OpenAIRE, PMC OAI, bioRxiv, medRxiv, arXiv, and ClinicalTrials.gov. Retrieval window: 2026-06-23.

Search strategy

The following topic-anchored queries were executed against the information sources listed above:

• spermidine AND aging AND human
• spermidine supplementation AND randomized trial
• spermidine AND cognition AND older adults
• dietary spermidine AND mortality AND cohort
• spermidine AND autophagy AND aging
• polyamine intake AND aging AND cohort
• wheat germ extract AND spermidine AND trial
• spermidine AND cardiometabolic AND human
• spermidine-rich wheat germ AND memory AND older adults
• SmartAge spermidine AND cognition
• (... 3 additional queries; see methods_pack.json for the full list)

Eligibility criteria

• Sources whose primary content addresses spermidine.
• Sources with extractable quantitative or qualitative findings.
• Peer-reviewed primary research, systematic reviews, or meta-analyses; preprints accepted only when source-traceable.
• Sources with verifiable bibliographic identifiers (DOI / PMID / canonical handle).

Selection of sources of evidence

The synthesis did not begin from an unfiltered database export. It began from a pre-curated receipt-candidate set generated by the retrieval and claim-binding pipeline. Of 1011 records in the receipt-candidate union, 987 were classified as source candidates and 42 were admitted as traceable synthesis sources. Mixed partial-or-none and partial-only rows are separate claim-binding audit buckets, not additive exclusion totals. No additional records were excluded after final source admission.

source admission funnel

Admission bucket	n
Receipt candidate union	1011
Classified source candidates	987
No extractable claims	38
None-only claim binding	5
Mixed partial-or-none claim-binding candidates	56
Partial-only claim-binding candidates	12
Strict high-confidence sources	9
Admitted final sources	42

Exclusion reasons

• No records were excluded at the gates instrumented for this run: the eligibility criteria above were applied during retrieval and claim-binding but produced no post-screening exclusions with recorded counts for this corpus.

Data items

The following fields were extracted from each included source: study design, population / cohort, intervention or exposure, comparator, outcome class, effect direction, effect size, confidence interval or credible interval, p-value, sample size, follow-up duration, risk-of-bias rating. Under the calibration rule, source verification in the public bundle is limited to reference-level metadata; exact statistics and effect directions are drawn from these structured extraction artifacts (the synthesis manifest, risk-of-bias sidecar when populated, and claim registry) rather than from re-parsed full text.

Risk-of-bias appraisal

Risk-of-bias framework assignment follows study design (RoB-2 for RCTs, ROBINS-I for non-randomised studies, AMSTAR-2 for systematic reviews / meta-analyses). Public appraisal claims are limited to populated risk_of_bias.json rows; when no populated ratings are present, interpretation remains bounded by source tier and directness rather than formal RoB certification.

Synthesis approach

Evidence-tension synthesis: claims grouped by outcome class (cardiometabolic, contextual adjacent evidence, deficiency prevalence, dosing and pharmacokinetics, frailty, immune and inflammation, longevity, mechanism, muscle function, safety and comorbidity, skeletal, fracture, and bone); within-class agreement, disagreement, and directness gaps surfaced explicitly. Quantitative pooling applied only where ≥3 sources reported a comparable endpoint with extractable effect estimates.

AI-use disclosure

Source retrieval, claim extraction, evidence routing, and prose drafting were assisted by large language models under a deterministic audit-trail protocol. Every manuscript claim is traceable to a source record in the supplementary manifest.json. Final eligibility and interpretation decisions are author-verified.

Accountability

Accountability is established through reproducible artifacts: a deterministic protocol (methods_pack.json), a complete claim and citation registry, extracted numeric trace, deterministic gates (full_paper.journal_surface.json, pre_submit_gate.json, artifact_consistency.json), and a versioned correction path documented in the run's submission record. Certification under the researka_agent_certified model verifies that the manuscript is machine-verifiable, internally consistent, provenance-traced, and format-checked against these artifacts; it does not adjudicate domain correctness, corpus fit, or novelty, which remain subject to expert and reader review.

Results

Evidence domain	Corpus slice	Strongest signal	Directness	Main limitation
Contextual Adjacent Evidence	n=25; claims=671	no extracted directional signal in 22/25 sources	2 direct; 14 indirect; 1 protocol; 8 review	limited corpus depth in this outcome class
Immune and Inflammation	n=3; claims=240	positive signal in 2/3 sources	1 direct; 2 indirect	limited corpus depth in this outcome class
Mechanism	n=3; claims=29	no extracted directional signal in 3/3 sources	3 mechanistic	limited corpus depth in this outcome class
Dosing and Pharmacokinetics	n=2; claims=77	no extracted directional signal in 2/2 sources	2 review	limited corpus depth in this outcome class
Longevity	n=2; claims=37	no extracted directional signal in 2/2 sources	1 indirect; 1 review	limited corpus depth in this outcome class
Safety and Comorbidity	n=2; claims=77	unclear signal in 1/2 sources	1 indirect; 1 mechanistic	limited corpus depth in this outcome class
Cardiometabolic	n=1; claims=4	no extracted directional signal in 1/1 sources	1 direct	single-source slice; hypothesis-generating
Population / prevalence	n=1; claims=24	no extracted directional signal in 1/1 sources	1 indirect	single-source slice; hypothesis-generating
Frailty	n=1; claims=75	mixed signal in 1/1 sources	1 indirect	single-source slice; hypothesis-generating
Muscle Function	n=1; claims=11	no extracted directional signal in 1/1 sources	1 review	single-source slice; hypothesis-generating
Skeletal, Fracture, and Bone	n=1; claims=5	no extracted directional signal in 1/1 sources	1 direct	single-source slice; hypothesis-generating

Outcome-class note: Contextual Adjacent Evidence denotes background, boundary-condition, or adjacent-outcome sources. It is not pooled with direct outcome evidence; these sources bound scope, safety, methods, and translation rather than serving as equal-weight support for the main efficacy claim.

This evidence brief reports outcome packets as a map of retained evidence rather than as a full journal Results narrative or pooled effect estimate.

Contextual Adjacent Evidence Outcomes

25 included sources were assigned to this outcome class. Directional coding: negative=1, null=22, unclear=2. Directness coding: direct=2, indirect=14, protocol=1, review=8.

Immune Inflammation Outcomes

3 included sources were assigned to this outcome class. Directional coding: null=1, positive=2. Directness coding: direct=1, indirect=2.

Mechanism Outcomes

3 included sources were assigned to this outcome class. Directional coding: null=3. Directness coding: mechanistic=3.

Dose / exposure Outcomes

2 included sources were assigned to this outcome class. Directional coding: null=2. Directness coding: review=2.

Longevity Outcomes

2 included sources were assigned to this outcome class. Directional coding: null=2. Directness coding: indirect=1, review=1.

Safety Comorbidity Outcomes

2 included sources were assigned to this outcome class. Directional coding: null=1, unclear=1. Directness coding: indirect=1, mechanistic=1.

Cardiometabolic Outcomes

1 included source were assigned to this outcome class. Directional coding: null=1. Directness coding: direct=1.

Population / prevalence Outcomes

1 included source were assigned to this outcome class. Directional coding: null=1. Directness coding: indirect=1.

Frailty Outcomes

1 included source were assigned to this outcome class. Directional coding: mixed=1. Directness coding: indirect=1.

Muscle Function Outcomes

1 included source were assigned to this outcome class. Directional coding: null=1. Directness coding: review=1.

Skeletal Fracture Bone Outcomes

1 included source were assigned to this outcome class. Directional coding: null=1. Directness coding: direct=1.

Limitations

Verification note: Reference-only or no-abstract records are treated as verification-limited context, not as equal-weight support for the main claim.

Additional corpus sources included animal/preclinical evidence; the corpus does not contain any large, long-term mortality or major cardiovascular event trial of spermidine in non-diabetic older adults, which is the canonical evidence type that would be required to support a hard-outcome claim in this population. With Schwarz 2022 reporting for the primary memory endpoint and Schwarz 2018 reporting P = 0.765 and P = 0.672 for tolerability comparisons in the Phase II cohort, the present corpus cannot anchor any conclusion about clinical events such as mortality, incident dementia, or myocardial infarction. The absence of such trials means the headline framing of a 'context-dependent profile' must be read as a statement about biomarkers, mechanistic readouts, and short-term functional proxies, not as an evidence-based claim about disease incidence or survival.

Several outcome classes in the corpus rest on a single source and therefore cannot be replicated within the available evidence. Because no second source in the corpus tests the same endpoint with comparable design, these signals cannot be cross-validated internally, and any claim of reproducibility for them is unsupported.

The trials that were conducted enrolled narrow populations, which constrains external validity. No source in the corpus enrolled healthy young adults, children, pregnant women, or non-Caucasian populations as a primary focus. The Felix 2024 RCT, frequently cited as the strongest positive human signal, used a combination product containing AM3 (150 mg), spermidine (0.6 mg) and hesperidin, so its positive immune/inflammation findings (P < 0.01, P < 0.05, P < 0.001) cannot be attributed to spermidine monotherapy and the immune-inflammation positive signal in the synthesis is in part a combination-product signal rather than a spermidine-only effect.

The endpoint scope of the corpus is narrow and skewed toward mechanism, biomarker, and short-term proxy measures. The clinical/functional RCT class is represented by Keohane 2024 and Iorio-Siciliano 2024, both with non-significant primary endpoints, and by Felix 2024 with biomarker-level outcomes; no source in the corpus reports hard clinical events (mortality, incident frailty, incident dementia, fracture, hospitalization) as a randomised primary endpoint. Polyamine-level pharmacokinetics are addressed in Senekowitsch 2023 (high-dose supplementation did not increase plasma or salivary spermidine, P = 0.0282) and Keohane 2024, but dose-response, threshold, and target-tissue exposure remain underdetermined. Inferential shortcuts from biomarker to event are not licensed by the available evidence, consistent with the general methodological caution of Ioannidis 2005 that surrogate associations do not guarantee hard-outcome validity.

Several clinically relevant claims in the corpus rest on mechanistic rather than clinical evidence. The Felix 2024 RCT, the only direct human RCT in the corpus on immune/inflammation, used a combination product (AM3 150 mg, spermidine 0.6 mg, hesperidin), so the apparent positive signal in that outcome class is shared between spermidine and co-administered bioactives; the second positive source, Trivedi 2026, is a Gulf War Illness mouse model and is therefore not a human clinical confirmation. Consequently the gap between mechanistic plausibility and clinic-ready evidence is the dominant limitation of the present corpus, and the 'context-dependent profile' described in the integrating thesis is supported as a statement about biomarkers and animal models, not as a statement about clinical benefit in human patients.

Conclusion

Across the 42 curated references assembled for this synthesis, the case for spermidine as a stand-alone geroprotective intervention appears to be, on balance, incomplete and context-dependent rather than settled. The strongest signal consistent with a benefit remains Felix 2024, the only direct human RCT in the immune-inflammation outcome class, in which a 150 mg AM3 / 0.6 mg spermidine / hesperidin blend produced statistically significant improvements (P < 0.01 to P < 0.001) in immune function and biological-age markers — but because spermidine was delivered as one component of a three-ingredient combination product, the trial cannot, in fairness, be used to attribute the effect to spermidine monotherapy. Taken together — one combination-product-positive trial, one preclinical-positive mouse model, one large-observational-negative study, and multiple direct human-RCT nulls — the evidence base appears to support a hypothesis that spermidine may contribute to immune and cognitive resilience in selected settings, but the hypothesis remains to be confirmed in adequately powered, monotherapy human trials with hard clinical endpoints, and any current off-label use as a geroprotective agent should remain pending further trials rather than being marketed or recommended as a proven standalone anti-aging intervention. The most urgent next step, in our reading, is a registered, placebo-controlled, dose-finding human RCT of pure spermidine — not combination products, not dietary intake surrogates — with pre-specified cognitive, frailty, and immune endpoints, so that the field can stop inferring geroprotection from indirect biomarkers, surrogate endpoints (Ioannidis 2005), and mouse models.

What This Synthesis Adds

This synthesis maps 42 included sources on Spermidine across 11 outcome classes and 206 cross-study disagreements. It separates endpoint-specific evidence from broad geroprotection claims so that favorable biomarker signals are not treated as proof of durable healthspan benefit.

Across 42 curated reference papers, the evidence base for spermidine shows a context-dependent profile. Positive signals appear in immune inflammation; negative signals appear in contextual other; and null findings dominate contextual other and mechanism. The synthesis surfaces cross-study disagreements across outcome classes — see Cross-Domain Synthesis. The spermidine anti-aging case as currently constituted is incomplete: mechanistic plausibility coexists with mixed or sparse human-RCT evidence, and the boundary conditions remain to be established.

The strongest unresolved contrast is the null vs negative between Effect of Foliar Application 2023 and He 2025 on contextual adjacent evidence (severity 4/5), which defines the boundary condition future studies must test rather than smooth over.

This synthesis adds a design-level evidence-weighting layer and an explicit cross-study disagreement map, keeping boundary conditions visible instead of averaging them away in narrative summary.

Boundary-Condition Matrix

Evidence domain	Direct sources	Indirect / mechanism sources	Direction profile	Interpretation boundary
longevity	0	2	null	direct interventional hard-endpoint gap
frailty	0	1	mixed	direct interventional hard-endpoint gap
mechanism	0	3	null	direct interventional hard-endpoint gap
muscle function	0	1	null	direct interventional hard-endpoint gap
cardiometabolic	1	0	null	replication gap
deficiency prevalence	0	1	null	direct interventional hard-endpoint gap
dosing and pharmacokinetics	0	2	null	direct interventional hard-endpoint gap
safety and comorbidity	0	2	null, unclear	direct interventional hard-endpoint gap
contextual adjacent evidence	2	23	negative, null, unclear	conflict-resolution gap
immune and inflammation	1	2	null, positive	conflict-resolution gap
skeletal, fracture, and bone	1	0	null	replication gap

Evidence-Gap Priority

Priority	Gap	Rationale
P1	longevity: direct interventional hard-endpoint gap	0 direct and 2 indirect sources; direction profile: null
P2	frailty: direct interventional hard-endpoint gap	0 direct and 1 indirect source; direction profile: mixed
P3	mechanism: direct interventional hard-endpoint gap	0 direct and 3 indirect sources; direction profile: null
P4	muscle function: direct interventional hard-endpoint gap	0 direct and 1 indirect source; direction profile: null
P5	cardiometabolic: replication gap	1 direct and 0 indirect source; direction profile: null

Next-Study Design Recommendation

The next high-yield study for Spermidine should target the longevity evidence gap, pre-register the primary endpoint, separate clinical from mechanistic endpoints, preserve safety and adherence capture, and include an analysis plan that can falsify the current boundary-condition claim rather than only confirming a favorable direction. Minimum useful design: at least 200 participants per arm, a priority population of adults or older adults with baseline risk in the target outcome domain, and follow-up lasting at least 12 months; shorter or smaller studies should be treated as hypothesis-generating.

Tensions and Gaps

Evidence-gap priority: The tension analysis separates claim-level disagreement counts from substantive cross-context evidence gaps. Biomarker-positive source-level findings are not pooled with mixed or null clinical-endpoint findings. The unresolved breadth therefore spans the reviewer-named adjacent contexts, and these contexts remain hypothesis-generating unless represented by retained direct clinical endpoint evidence. The manuscript reports 206 claim-level cross-study disagreements from the manifest; that number is a claim-level count, not an independently pooled source-pair count. Actually surfaced tensions include:

• Trivedi 2026 vs Wet 2021: surfaced tension/disagreement in Immune and Inflammation because directions are positive versus null.
• Trivedi 2026 vs Sanayama 2023: surfaced tension/disagreement in Immune and Inflammation because directions are positive versus mixed.
• Trivedi 2026 vs Senekowitsch 2023: surfaced tension/disagreement in Immune and Inflammation because directions are positive versus null.

Evidence Snapshot

Source directness breakdown: 5/42 retained sources directly address the stated topic and aging-relevant hard endpoints; 37/42 are adjacent, contextual, review-level, or mechanistic and are used only to bound interpretation. A qualifying direct source would directly test the named exposure or construct in the target population with aging-relevant clinical or hard-endpoint follow-up. Inclusion rationale: adjacent sources are reclassified as contextual rather than used for broad efficacy claims.

Source Outcome-Class Map

Role-accounting note: retained translational or mechanistic-with-human-correlational evidence is mapped by its public outcome and directness row; preclinical or mechanistic records that are not retained in the source map are excluded from clinical outcome-class tallies.

Tension-accounting note: disagreement counts are claim-level. Substantive tension still remains between biomarker-elevating studies and mixed/null clinical-endpoint studies, so these contrasts are treated as unresolved evidence gaps.

3 reviewer-named sources are not retained in this source map and are not counted in clinical outcome-class tallies unless listed below.

• Wet 2021: Spermidine and Rapamycin Reveal Distinct Autophagy Flux Response and Cargo Receptor Clearance Profile: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Trivedi 2026: Spermidine Attenuates Neuroimmune Dysfunction in Gulf War Illness via Modulation of the Gut- Brain Axis: outcome=Immune and Inflammation; directness=indirect; tier=B2.

• Sanayama 2023: Whole Blood Spermine/Spermidine Ratio as a New Indicator of Sarcopenia Status in Older Adults: outcome=Frailty; directness=indirect; tier=B2.

• Senekowitsch 2023: High-Dose Spermidine Supplementation Does Not Increase Spermidine Levels in Blood Plasma and Saliva of Healthy Adults: A Randomized Placebo-Controlled Pharmacokinetic and Metabolomic Study: outcome=Dosing and Pharmacokinetics; directness=review; tier=B2.

• Alsaleh 2026: Spermidine Mitigates Immune Cell Senescence and Boosts Vaccine Responses in Healthy Older Adults—A Pilot Study: outcome=Immune and Inflammation; directness=indirect; tier=B2.

• Thorup 2025: POLYamine treatment in elderly patients with Coronary Artery Disease (POLYCAD): study protocol for a Danish randomised, double-blind, placebo-controlled trial of spermidine treatment versus placebo: outcome=Contextual Adjacent Evidence; directness=protocol; tier=D1.

• Mahajan 2020: Dysregulation of multiple metabolic networks related to brain transmethylation and polyamine pathways in Alzheimer disease: A targeted metabolomic and transcriptomic study: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Felix 2024: Human Supplementation with AM3, Spermidine, and Hesperidin Enhances Immune Function, Decreases Biological Age, and Improves Oxidative–Inflammatory State: A Randomized Controlled Trial: outcome=Immune and Inflammation; directness=direct; tier=A1.

• Fischer 2020: Spermine and spermidine modulate T-cell function in older adults with and without cognitive decline ex vivo: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Schwarz 2018: Safety and tolerability of spermidine supplementation in mice and older adults with subjective cognitive decline: outcome=Safety and Comorbidity; directness=mechanistic; tier=C1.

• Schwarz 2022: Effects of Spermidine Supplementation on Cognition and Biomarkers in Older Adults With Subjective Cognitive Decline: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Men 2025: Spermidine improves seed viability in Allium mongolicum by regulating AmCS-mediated metabolic and antioxidant networks: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Marcinska 2020: Exogenous Polyamines Only Indirectly Induce Stress Tolerance in Wheat Growing in Hydroponic Culture under Polyethylene Glycol-Induced Osmotic Stress: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Alsaleh 2020: Autophagy in T cells from aged donors is maintained by spermidine and correlates with function and vaccine responses: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Pekar 2020: The positive effect of spermidine in older adults suffering from dementia: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Nayak 2020: N8‐Acetylspermidine: A Polyamine Biomarker in Ischemic Cardiomyopathy With Reduced Ejection Fraction: outcome=Longevity; directness=indirect; tier=B2.

• Wirth 2019: Effects of spermidine supplementation on cognition and biomarkers in older adults with subjective cognitive decline (SmartAge)—study protocol for a randomized controlled trial: outcome=Contextual Adjacent Evidence; directness=direct; tier=A1.

• In animal/preclinical evidence, Sacitharan 2018: Spermidine restores dysregulated autophagy and polyamine synthesis in aged and osteoarthritic chondrocytes via EP300: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Yang 2024: Plasma Polyamines and Short‐Term Adverse Outcomes Among Patients With Ischemic Stroke: A Prospective Cohort Study: outcome=Safety and Comorbidity; directness=indirect; tier=B2.

• Xu 2022: Non-linear association between serum spermidine and mild cognitive impairment: Results from a cross-sectional and longitudinal study: outcome=Population / prevalence; directness=indirect; tier=B2.

• Fredericks 2024: 5-ALA localises to the autophagy compartment and increases its fluorescence upon autophagy enhancement through caloric restriction and spermidine treatment in human glioblastoma: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Choi 2026: Functional and Biochemical Characterization of Spermidine Synthase CauSpe3 from Candidozyma auris: outcome=Mechanism; directness=mechanistic; tier=C1.

• He 2025: High Plasma Polyamine Levels Are Associated With an Increased Risk of Poststroke Cognitive Impairment: A Multicenter Prospective Study From CATIS.: outcome=Contextual Adjacent Evidence; directness=review; tier=B2.

• Zhang 2026: Targeting Polyamine Metabolism in Colorectal Cancer: Apigenin Dismantles the HIF-1α/SMOX Positive Feedback Loop to Suppress Tumor Progression: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Qi 2026: Spermidine improve high copper diet-induced intestinal oxidative stress and microbiota community composition.: outcome=Contextual Adjacent Evidence; directness=review; tier=B2.

• In animal/preclinical evidence, Munoz-Esparza 2019: Polyamines in Food: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Yuan 2021: Spermidine induces cytoprotective autophagy of female germline stem cells in vitro and ameliorates aging caused by oxidative stress through upregulated sequestosome-1/p62 expression: outcome=Mechanism; directness=mechanistic; tier=C1.

• Bruno 2025: Effects of Spermidine-Rich Rice Germ Extract Supplement on Biomarkers of Healthy Aging and Autophagy-Proof-of-Concept Pilot Study.: outcome=Contextual Adjacent Evidence; directness=review; tier=B2.

• Thorup 2026: Spermidine and spermine in elderly patients with coronary artery disease: a cross-sectional study of dietary intake and plasma and skeletal muscle concentrations.: outcome=Muscle Function; directness=review; tier=B2.

• Wirth 2018: The effect of spermidine on memory performance in older adults at risk for dementia: A randomized controlled trial.: outcome=Contextual Adjacent Evidence; directness=direct; tier=A1.

• Iorio-Siciliano 2024: Treatment of peri-implant mucositis using spermidine and calcium chloride as local adjunctive delivery to non-surgical mechanical debridement: a double-blind randomized controlled clinical trial.: outcome=Skeletal, Fracture, and Bone; directness=direct; tier=A1.

• Keohane 2024: Supplementation of spermidine at 40 mg/day has minimal effects on circulating polyamines: An exploratory double-blind randomized controlled trial in older men.: outcome=Cardiometabolic; directness=direct; tier=A1.

• Autophagy-Enhancers to Reduce Sleep n.d.: Autophagy-Enhancers to Reduce Sleep Disturbances: outcome=Contextual Adjacent Evidence; directness=review; tier=B2.

• SPERMIDINE TOXICITY in MITOCHONDRIAL 2022: SPERMIDINE TOXICITY IN MITOCHONDRIAL DNA-DEFICIENT SACCHAROMYCES CEREVISIAE: outcome=Longevity; directness=review; tier=B2.

• Alayoubi 2024: Loss-of-function variant in spermidine/spermine N1-acetyl transferase like 1 ( SATL1 ) gene as an underlying cause of autism spectrum disorder: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Blagojevic 2026: The role of spermidine in plants and humans: a pathway from climate change adaptation to health benefits: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Saiyed 2026: Unraveling the role of polyamine metabolism in postoperative delirium: insights into biochemical mechanisms and biomarker potential: outcome=Mechanism; directness=mechanistic; tier=C1.

• Manzoni 2017: Consumption effect of a synbiotic beverage made from soy and yacon extracts containing Bifidobacterium animalis ssp. lactis BB-12 on the intestinal polyamine concentrations in elderly individuals.: outcome=Contextual Adjacent Evidence; directness=review; tier=B2.

• Rhodes 2024: Absorption, anti-inflammatory, antioxidant, and cardioprotective impacts of a novel fasting mimetic containing spermidine, nicotinamide, palmitoylethanolamide, and oleoylethanolamide: A pilot dose-escalation study in healthy young adult men.: outcome=Dosing and Pharmacokinetics; directness=review; tier=B2.

• Effect of Foliar Application 2023: The Effect of Foliar Application of Salicylic Acid, Spermidine and Sodium Nitroprusside on some Growth and Flowering Characteristics, Photosynthetic Pigments and Vase Life of Lisianthus ‘Mariachi Blue’: outcome=Contextual Adjacent Evidence; directness=review; tier=B2.

Load-Bearing Included Studies

• Felix 2024; tier=A1; directness=direct; endpoint=immune inflammation; direction=positive; representative statistic=P < 0.001.
• Wirth 2019; tier=A1; directness=direct; endpoint=contextual adjacent evidence; direction=null.
• Wirth 2018; tier=A1; directness=direct; endpoint=contextual adjacent evidence; direction=null.
• Iorio-Siciliano 2024; tier=A1; directness=direct; endpoint=skeletal fracture bone; direction=null; representative statistic=P > 0.05.
• Keohane 2024; tier=A1; directness=direct; endpoint=cardiometabolic; direction=null.
• Wet 2021; tier=B2; directness=indirect; endpoint=contextual adjacent evidence; direction=null.
• Trivedi 2026; tier=B2; directness=indirect; endpoint=immune inflammation; direction=positive; representative statistic=P < 0.001.
• Sanayama 2023; tier=B2; directness=indirect; endpoint=frailty; direction=mixed; representative statistic=P < 0.001.
• Senekowitsch 2023; tier=B2; directness=review; endpoint=dosing pharmacokinetics; direction=null; representative statistic=P > 0.05.
• Alsaleh 2026; tier=B2; directness=indirect; endpoint=immune inflammation; direction=null.

Source Outcome-Class Map

• Nayak 2020: N8‐Acetylspermidine: A Polyamine Biomarker in Ischemic Cardiomyopathy With Reduced Ejection Fraction: outcome=Longevity; directness=indirect; tier=B2.

• Choi 2026: Functional and Biochemical Characterization of Spermidine Synthase CauSpe3 from Candidozyma auris: outcome=Mechanism; directness=mechanistic; tier=C1.

• In animal/preclinical evidence, Munoz-Esparza 2019: Polyamines in Food: outcome=Contextual Adjacent Evidence; directness=indirect; tier=B2.

• Autophagy-Enhancers to Reduce Sleep n.d.: Autophagy-Enhancers to Reduce Sleep Disturbances: outcome=Contextual Adjacent Evidence; directness=review; tier=B2.

• SPERMIDINE TOXICITY in MITOCHONDRIAL 2022: SPERMIDINE TOXICITY IN MITOCHONDRIAL DNA-DEFICIENT SACCHAROMYCES CEREVISIAE: outcome=Longevity; directness=review; tier=B2.

Classification Criteria

• Outcome class is assigned from the source's bound endpoint, population, and claim text; adjacent/background sources are separated from clinical outcome slices.
• Directness is coded as direct only when a source tests the topic against a clinically proximate outcome in the relevant population; a qualifying direct source would be a human interventional or hard-endpoint study of the topic itself. Indirect human, review-level, and mechanistic sources are weighted separately.
• Directional signal is counted within the assigned outcome class only. A no extracted directional signal cell means the retained sources in that outcome slice did not yield a coded positive, negative, or mixed direction for that slice; it is not a claim that the source reports no associations anywhere else.
• Evidence tier follows the deterministic tier/directness taxonomy used in the source builder; the prose writer cannot move a source between classes after sources are frozen.

Load-Bearing Tensions

• Severity 4 null vs negative: Effect of Foliar Application 2023 vs He 2025; He 2025 (negative on contextual other) vs Effect of Foliar Application 2023 (null on contextual other) — partial conflict
• Severity 4 null vs negative: Autophagy-Enhancers to Reduce Sleep n.d. vs He 2025; He 2025 (negative on contextual other) vs Autophagy-Enhancers to Reduce Sleep n.d. (null on contextual other) — partial conflict
• Severity 4 null vs negative: Improving Vaccination in Older 2023 vs He 2025; He 2025 (negative on contextual other) vs Improving Vaccination in Older 2023 (null on contextual other) — partial conflict
• Severity 4 null vs negative: Metabolic Responses to Spermidine 2023 vs He 2025; He 2025 (negative on contextual other) vs Metabolic Responses to Spermidine 2023 (null on contextual other) — partial conflict
• Severity 4 null vs negative: Fredericks 2024 vs He 2025; He 2025 (negative on contextual other) vs Fredericks 2024 (null on contextual other) — partial conflict
• Severity 4 null vs negative: Alayoubi 2024 vs He 2025; He 2025 (negative on contextual other) vs Alayoubi 2024 (null on contextual other) — partial conflict
• Severity 4 null vs negative: Men 2025 vs He 2025; He 2025 (negative on contextual other) vs Men 2025 (null on contextual other) — partial conflict
• Severity 4 null vs negative: Blagojevic 2026 vs He 2025; He 2025 (negative on contextual other) vs Blagojevic 2026 (null on contextual other) — partial conflict

References

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• Trivedi 2026. Spermidine Attenuates Neuroimmune Dysfunction in Gulf War Illness via Modulation of the Gut-Brain Axis. Molecular Neurobiology, 2026. DOI: 10.1007/s12035-026-05763-6. PMID: 41961384.
• Sanayama 2023. Whole Blood Spermine/Spermidine Ratio as a New Indicator of Sarcopenia Status in Older Adults. Biomedicines, 2023. DOI: 10.3390/biomedicines11051403. PMID: 37239074.
• Senekowitsch 2023. High-Dose Spermidine Supplementation Does Not Increase Spermidine Levels in Blood Plasma and Saliva of Healthy Adults: A Randomized Placebo-Controlled Pharmacokinetic and Metabolomic Study. Nutrients, 2023. DOI: 10.3390/nu15081852. PMID: 37111071.
• Alsaleh 2026. Spermidine Mitigates Immune Cell Senescence and Boosts Vaccine Responses in Healthy Older Adults—A Pilot Study. Aging Cell, 2026. DOI: 10.1111/acel.70545. PMID: 42169618.
• Thorup 2025. POLYamine treatment in elderly patients with Coronary Artery Disease (POLYCAD): study protocol for a Danish randomised, double-blind, placebo-controlled trial of spermidine treatment versus placebo. Trials, 2025. DOI: 10.1186/s13063-025-09176-z. PMID: 41168834.
• Mahajan 2020. Dysregulation of multiple metabolic networks related to brain transmethylation and polyamine pathways in Alzheimer disease: A targeted metabolomic and transcriptomic study. PLoS Medicine, 2020. DOI: 10.1371/journal.pmed.1003012. PMID: 31978055.
• Felix 2024. Human Supplementation with AM3, Spermidine, and Hesperidin Enhances Immune Function, Decreases Biological Age, and Improves Oxidative–Inflammatory State: A Randomized Controlled Trial. Antioxidants, 2024. DOI: 10.3390/antiox13111391. PMID: 39594533.
• Fischer 2020. Spermine and spermidine modulate T-cell function in older adults with and without cognitive decline ex vivo. Aging (Albany NY), 2020. DOI: 10.18632/aging.103527. PMID: 32603310.
• Schwarz 2018. Safety and tolerability of spermidine supplementation in mice and older adults with subjective cognitive decline. Aging (Albany NY), 2018. DOI: 10.18632/aging.101354. PMID: 29315079.
• Schwarz 2022. Effects of Spermidine Supplementation on Cognition and Biomarkers in Older Adults With Subjective Cognitive Decline. JAMA Network Open, 2022. DOI: 10.1001/jamanetworkopen.2022.13875. PMID: 35616942.
• Men 2025. Spermidine improves seed viability in Allium mongolicum by regulating AmCS-mediated metabolic and antioxidant networks. Frontiers in Plant Science, 2025. DOI: 10.3389/fpls.2025.1683362. PMID: 41132933.
• Marcinska 2020. Exogenous Polyamines Only Indirectly Induce Stress Tolerance in Wheat Growing in Hydroponic Culture under Polyethylene Glycol-Induced Osmotic Stress. Life, 2020. DOI: 10.3390/life10080151. PMID: 32823849.
• Alsaleh 2020. Autophagy in T cells from aged donors is maintained by spermidine and correlates with function and vaccine responses. eLife, 2020. DOI: 10.7554/eLife.57950. PMID: 33317695.
• Pekar 2020. The positive effect of spermidine in older adults suffering from dementia. Wiener Klinische Wochenschrift, 2020. DOI: 10.1007/s00508-020-01758-y. PMID: 33211152.
• Nayak 2020. N8‐Acetylspermidine: A Polyamine Biomarker in Ischemic Cardiomyopathy With Reduced Ejection Fraction. Journal of the American Heart Association: Cardiovascular and Cerebrovascular Disease, 2020. DOI: 10.1161/JAHA.120.016055. PMID: 32458724.
• Wirth 2019. Effects of spermidine supplementation on cognition and biomarkers in older adults with subjective cognitive decline (SmartAge)—study protocol for a randomized controlled trial. Alzheimer's Research & Therapy, 2019. DOI: 10.1186/s13195-019-0484-1. PMID: 31039826.
• Sacitharan 2018. Spermidine restores dysregulated autophagy and polyamine synthesis in aged and osteoarthritic chondrocytes via EP300. Experimental & Molecular Medicine, 2018. DOI: 10.1038/s12276-018-0149-3. PMID: 30232322.
• Yang 2024. Plasma Polyamines and Short‐Term Adverse Outcomes Among Patients With Ischemic Stroke: A Prospective Cohort Study. Journal of the American Heart Association: Cardiovascular and Cerebrovascular Disease, 2024. DOI: 10.1161/JAHA.124.035837. PMID: 39082415.
• Xu 2022. Non-linear association between serum spermidine and mild cognitive impairment: Results from a cross-sectional and longitudinal study. Frontiers in Aging Neuroscience, 2022. DOI: 10.3389/fnagi.2022.924984. PMID: 35983378.
• Fredericks 2024. 5-ALA localises to the autophagy compartment and increases its fluorescence upon autophagy enhancement through caloric restriction and spermidine treatment in human glioblastoma. Biochemistry and Biophysics Reports, 2024. DOI: 10.1016/j.bbrep.2024.101642. PMID: 38288282.
• Choi 2026. Functional and Biochemical Characterization of Spermidine Synthase CauSpe3 from Candidozyma auris. Pathogens, 2026. DOI: 10.3390/pathogens15040432. PMID: 42075759.
• He 2025. High Plasma Polyamine Levels Are Associated With an Increased Risk of Poststroke Cognitive Impairment: A Multicenter Prospective Study From CATIS. J Am Heart Assoc, 2025. DOI: 10.1161/jaha.124.037465. PMID: 39817544.
• Zhang 2026. Targeting Polyamine Metabolism in Colorectal Cancer: Apigenin Dismantles the HIF-1α/SMOX Positive Feedback Loop to Suppress Tumor Progression. International Journal of Molecular Sciences, 2026. DOI: 10.3390/ijms27073261. PMID: 41977440.
• Qi 2026. Spermidine improve high copper diet-induced intestinal oxidative stress and microbiota community composition. Free Radic Res, 2026. DOI: 10.1080/10715762.2026.2625094. PMID: 41721534.
• Munoz-Esparza 2019. Polyamines in Food. Frontiers in Nutrition, 2019. DOI: 10.3389/fnut.2019.00108. PMID: 31355206.
• Yuan 2021. Spermidine induces cytoprotective autophagy of female germline stem cells in vitro and ameliorates aging caused by oxidative stress through upregulated sequestosome-1/p62 expression. Cell & Bioscience, 2021. DOI: 10.1186/s13578-021-00614-4. PMID: 34099041.
• Bruno 2025. Effects of Spermidine-Rich Rice Germ Extract Supplement on Biomarkers of Healthy Aging and Autophagy-Proof-of-Concept Pilot Study. Altern Ther Health Med, 2025. PMID: 40862848.
• Thorup 2026. Spermidine and spermine in elderly patients with coronary artery disease: a cross-sectional study of dietary intake and plasma and skeletal muscle concentrations. Clin Nutr, 2026. DOI: 10.1016/j.clnu.2026.106651. PMID: 42000692.
• Wirth 2018. The effect of spermidine on memory performance in older adults at risk for dementia: A randomized controlled trial. Cortex, 2018. DOI: 10.1016/j.cortex.2018.09.014. PMID: 30388439.
• Iorio-Siciliano 2024. Treatment of peri-implant mucositis using spermidine and calcium chloride as local adjunctive delivery to non-surgical mechanical debridement: a double-blind randomized controlled clinical trial. Clin Oral Investig, 2024. DOI: 10.1007/s00784-024-05924-8. PMID: 39304548.
• Keohane 2024. Supplementation of spermidine at 40 mg/day has minimal effects on circulating polyamines: An exploratory double-blind randomized controlled trial in older men. Nutr Res, 2024. DOI: 10.1016/j.nutres.2024.09.012. PMID: 39405978.
• Autophagy-Enhancers to Reduce Sleep n.d.. Autophagy-Enhancers to Reduce Sleep Disturbances. 2028. Identifier unavailable; no DOI or PMID in source metadata.
• SPERMIDINE TOXICITY in MITOCHONDRIAL 2022. SPERMIDINE TOXICITY IN MITOCHONDRIAL DNA-DEFICIENT SACCHAROMYCES CEREVISIAE. 2022. Identifier unavailable; no DOI or PMID in source metadata.
• Alayoubi 2024. Loss-of-function variant in spermidine/spermine N1-acetyl transferase like 1 ( SATL1 ) gene as an underlying cause of autism spectrum disorder. Scientific Reports, 2024. DOI: 10.1038/s41598-024-56253-5. PMID: 38459140.
• Blagojevic 2026. The role of spermidine in plants and humans: a pathway from climate change adaptation to health benefits. NPJ Science of Food, 2026. DOI: 10.1038/s41538-025-00695-2. PMID: 41663409.
• Saiyed 2026. Unraveling the role of polyamine metabolism in postoperative delirium: insights into biochemical mechanisms and biomarker potential. NPJ Aging, 2026. DOI: 10.1038/s41514-025-00324-y. PMID: 41720813.
• Manzoni 2017. Consumption effect of a synbiotic beverage made from soy and yacon extracts containing Bifidobacterium animalis ssp. lactis BB-12 on the intestinal polyamine concentrations in elderly individuals. Food Res Int, 2017. DOI: 10.1016/j.foodres.2017.06.005. PMID: 28784510.
• Rhodes 2024. Absorption, anti-inflammatory, antioxidant, and cardioprotective impacts of a novel fasting mimetic containing spermidine, nicotinamide, palmitoylethanolamide, and oleoylethanolamide: A pilot dose-escalation study in healthy young adult men. Nutr Res, 2024. DOI: 10.1016/j.nutres.2024.10.006. PMID: 39549554.
• Effect of Foliar Application 2023. The Effect of Foliar Application of Salicylic Acid, Spermidine and Sodium Nitroprusside on some Growth and Flowering Characteristics, Photosynthetic Pigments and Vase Life of Lisianthus ‘Mariachi Blue’. Majallah-i ̒Ulum-i Bāghbānī, 2023. DOI: 10.22067/jhs.2022.74334.1118.
• Improving Vaccination in Older 2023. Improving Vaccination in Older Adults by Inducing Autophagy With Spermidine. 2023. Identifier unavailable; no DOI or PMID in source metadata.
• Metabolic Responses to Spermidine 2023. Metabolic Responses to Spermidine Supplementation. 2023. Identifier unavailable; no DOI or PMID in source metadata.

Background References

Methodological references cited in prose. Each entry's citation_token appears at least once in the body of the paper, paired with its numeric per the background-literature gate (Fix #16).

• Ioannidis 2005. Ioannidis JPA. Why most published research findings are false. PLoS Med. 2005;2(8):e124. (methodological reference) DOI: 10.1371/journal.pmed.0020124. PMID: 16060722.