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Observational evidence

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32 results

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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Erythrocyte long-chain omega-3 fatty acid levels are inversely associated with mortality and with incident cardiovascular disease: The Framingham Heart Study

Moderate
Omega-3 IndexObservational evidence
Observational study
Highest vs lowest Omega-3 Index quintile associated with 34% lower risk of death from any cause in the Framingham Offspring Cohort (n=2500, median 7.3-year follow-up)
Causal status: Associational; biologically plausible anti-inflammatory/anti-arrhythmic mechanism, but single cohort, not RCT-confirmed for mortality
Reliability / bias notes: Relatively short follow-up and single baseline measurement; modest sample size and event count (350 deaths)
Harris et al · J Clin Lipidol · 2018 · PMID 29559306
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Risk thresholds for alcohol consumption: combined IPD analysis of 599,912 current drinkers

Strong
AlcoholConfounding riskObservational evidence
Observational study
Large IPD analysis: mortality lowest around or below 100 g ethanol/week; higher intake progressively associated with lower life expectancy
Causal status: Association; causal interpretation complicated by abstainer/former-drinker bias
Reliability / bias notes: Former-drinker bias; drinking pattern and socioeconomic confounding
Wood et al · Lancet · 2018 · PMID 29676281
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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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Leisure time physical activity and mortality: detailed pooled dose-response relationship

Strong
SportObservational evidenceReverse causation risk
Observational study
Highest vs lowest activity roughly 25–35% lower mortality in major prospective meta-analyses
Causal status: Mostly association; causal support substantial but mortality RCT evidence limited
Reliability / bias notes: Reverse causation; questionnaire error; healthy-user bias
Arem et al · JAMA Intern Med · 2015 · PMID 25844730
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Tobacco smoking and all-cause mortality in a large Australian cohort study

Strong
SmokingObservational evidenceReverse causation riskSelf-report bias
Cohort study
Never smoker = reference; current smoking ~2.18–2.81× mortality in large cohorts; former smokers can approach never-smoker risk after prolonged cessation
Causal status: Causal support strong; mortality evidence mostly prospective
Reliability / bias notes: Self-report; pack-years and cessation timing matter; reverse causation can affect recent quitters
Banks et al · BMC Med · 2015 · PMID 25857449
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