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Meta-analysis

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16 results

Systematic review and meta-analysis of helmet use and helmet laws to reduce mortality in adult motorcycle riders

Strong for helmet protection; insufficient for riding itself
Motorcycle ridingConfounding riskMeta-analysisObservational evidence
Systematic review & meta-analysis
Helmet use mortality OR ~0.48 in recent meta-analysis; other cohorts ~0.65
Causal status: Strong for helmet intervention; riding-vs-nonriding mortality effect not cleanly estimated
Reliability / bias notes: Confounding by riding behaviour, speed, alcohol, road exposure; helmet evidence often crash-conditioned
Ratnasekera et al. · 2025 · PMID 40462278
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Low skeletal muscle mass index and all-cause mortality risk in adults: A systematic review and meta-analysis of prospective cohort studies

Strong
Muscle massMeta-analysisObservational evidenceSystematic review
Systematic review & meta-analysis
Low skeletal muscle mass index associated with 57% higher all-cause mortality risk (pooled RR 1.57, 95% CI 1.25–1.96) across 16 prospective studies, 81,358 participants
Causal status: Associational; prospective cohort evidence, biologically plausible via frailty/functional decline pathway
Reliability / bias notes: Heterogeneous SMI definitions across studies; risk magnitude varies substantially by BMI subgroup
Wang et al · PLoS One · 2023 · PMID 37285331
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Systematic review and meta-analysis of 90 cohort studies of social isolation, loneliness and mortality

Strong for association
Social connectionConfounding riskMeta-analysisObservational evidence
Systematic review & meta-analysis
90-cohort meta-analysis: isolation pooled effect ~1.32; loneliness ~1.14 for all-cause mortality
Causal status: Association; intervention evidence for mortality less direct
Reliability / bias notes: Definitions differ; loneliness ≠ isolation; socioeconomic/health confounding
Wang et al · Nat Hum Behav · 2023 · PMID 37337095
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Association of low-density lipoprotein cholesterol levels with the risk of mortality and cardiovascular events: A meta-analysis of cohort studies with 1,232,694 participants

Moderate
LDL cholesterolLarge cohort (100k+)Meta-analysisObservational evidence
Meta-analysis
LDL-C ≥160 mg/dL associated with higher all-cause mortality (RR 1.34, 95% CI 1.00–1.80) and CVD death (RR 1.79, 95% CI 1.26–2.54) vs LDL-C 70–129 mg/dL, in a meta-analysis of 1,232,694 adults
Causal status: Causal support strong for CVD via Mendelian randomization and RCTs; all-cause mortality signal weaker/borderline
Reliability / bias notes: All-cause mortality CI crosses 1.0; relationship appears non-linear/U-shaped, complicated by reverse causation in low-LDL groups (illness-driven cholesterol decline)
Peng et al · Medicine · 2022 · PMID 36482567
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Resistance Training and Mortality Risk: A Systematic Review and Meta-Analysis

Strong
Resistance TrainingMeta-analysisObservational evidenceSelf-report bias
Systematic review & meta-analysis
Any resistance training vs none associated with 15% lower all-cause mortality (RR 0.85, 95% CI 0.77–0.93); dose-response peaked at ~60 min/week (27% reduction)
Causal status: Observational; supported by RCT evidence on intermediate outcomes
Reliability / bias notes: Only 10 cohort studies pooled; self-reported exposure; nonlinear dose-response not fully resolved
Shailendra et al · Am J Prev Med · 2022 · PMID 35599175
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Marital status and risk of cardiovascular, cancer and all-cause mortality: systematic review and meta-analysis

Moderate–strong
Relationship statusConfounding riskMeta-analysisObservational evidence
Systematic review & meta-analysis
2025 pooled estimate: single HR ~1.55; divorced ~1.39; widowed ~1.43 vs married
Causal status: Association
Reliability / bias notes: Health selection into/out of relationships; social support and income confounding
Wang et al. · 2020 · PMID 32161813
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Quantitative risk of positive family history in developing colorectal cancer: A meta-analysis

Moderate
Hereditary CancerMeta-analysisObservational evidence
Meta-analysis
First-degree relative with colorectal cancer associated with 1.87x risk of colorectal cancer (95% CI 1.68–2.09) in a pooled analysis of 46 studies
Causal status: Associational; shared genetics and environment both contribute
Reliability / bias notes: Colorectal-cancer-specific, not all cancer sites; this pooled estimate does not stratify by the relative's age at diagnosis (the under-60 cutoff used in our question could not be verified against a single landmark source)
Mehraban Far et al · World J Gastroenterol · 2019 · PMID 31435179
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Fruit and vegetable intake and all-cause mortality: systematic review and dose-response meta-analysis

Moderate–strong
Fruits and vegetablesConfounding riskMeta-analysisObservational evidence
Systematic review & meta-analysis
~10% lower all-cause mortality per 200 g/day increase in combined intake; older cohorts suggest benefit around ~5 servings/day
Causal status: Association
Reliability / bias notes: Dietary measurement error; healthy lifestyle clustering; socioeconomic confounding
Aune et al. · 2017 · PMID 28338764
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BMI and all-cause mortality: IPD meta-analysis of 239 prospective studies

Strong
Body Mass Index (BMI)Meta-analysisObservational evidenceReverse causation risk
Meta-analysis
Vs BMI 22.5–<25: obesity 30–<35 HR 1.45; 35–<40 HR 1.94; 40–<60 HR 2.76
Causal status: Predominantly association; causal contribution plausible
Reliability / bias notes: Muscle mass and fat distribution; low-BMI reverse causation
Global BMI Mortality Collaboration · Lancet · 2016 · PMID 27423262
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Blood pressure lowering for prevention of cardiovascular disease and death: systematic review and meta-analysis

Strongest tier
Blood PressureInterventional / RCT evidenceMeta-analysisSystematic review
Systematic review & meta-analysis
~10 mmHg SBP lowering in RCT meta-analysis reduced all-cause mortality RR 0.87; observational 20 mmHg higher usual SBP materially increased vascular mortality
Causal status: Strong randomized/interventional evidence
Reliability / bias notes: Treatment status, age, white-coat effect, overtreatment; lower is not always better
Ettehad et al · Lancet · 2016 · PMID 26724178
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