Cohort studyindependent cross-checkabstract only checked★ key study I-CAN-01 in-depth review
Smokers die about ten years earlier; quitting gives years back
Mortality in relation to smoking: 50 years' observations on male British doctors.
Overview
Doll R et al.. BMJ 2004 · PMID 15213107 · DOI 10.1136/bmj.38142.554479.AE
Smoking tripled death rates; stopping at 30 avoided almost all the excess risk.
Does the study support the specific claim? No · Methodological quality: high
Plain-language summary
Study explained simply
- What did the researchers want to find out?
Measure smoking hazards over 50 years.
- How was the study done?
Prospective cohort.
- How many people, animals or samples were studied?
34,439 doctors.
- What was actually found?
Smokers die ~10 years earlier.
- How large was the observed effect?
3-fold mortality.
- What do the results mean in everyday life?
Stopping smoking at any age helps.
- What are the study's limitations?
Men only.
- What does it say about Elawady's specific claim?
Contradicts smoking dismissal.
- Do the results apply to Germany and Europe?
High.
- What can explicitly not be concluded from this study?
Effects of other tobacco products.
Scientific in-depth review
1. Full reference
- Authors
- Doll R et al.
- Journal
- BMJ
- Year
- 2004
- Identifier
- PMID 15213107 DOI 10.1136/bmj.38142.554479.AE
- Verification
- verified – PubMed esummary + efetch 2026-10-25
- Retracted
- no
- Corrections
- none
- Extent checked
- abstract only
- Conflicts of interest and funding
not stated in abstract
2. Research question
Hazards of smoking and benefits of cessation.
3. Study design and population
- Study design
- Cohort study – Prospective cohort, 50 years
- Population
Male British doctors
- Country
UK
- Period
1951-2001
- Sample size
34,439
- Inclusion and exclusion criteria
Male doctors responding in 1951
4. Methods and endpoints
- Exposure / intervention
Cigarette smoking
- Comparator
Lifelong non-smokers; ex-smokers
- Endpoints
Cause-specific and overall mortality
- Statistical methods
Rate ratios; life expectancy
5. Actual results
- Results
Continuing smokers born 1900-1930 died about 10 years younger than lifelong non-smokers; excess deaths chiefly vascular, neoplastic and respiratory. Cessation at 60, 50, 40, 30 gained about 3, 6, 9, 10 years. Among men born around 1920, prolonged smoking tripled age-specific mortality; stopping at 50 halved the hazard, at 30 avoided almost all of it.
- Absolute risks
Death in middle age 43% vs 15% (smokers vs non-smokers born in the 1920s)
- Authors' conclusion
Prolonged smoking tripled mortality; cessation substantially reduces risk.
6. Strengths
- 50-year prospective follow-up
- Repeated exposure assessment
7. Weaknesses
- Men, doctors only
8. Risk of bias
- Orienting tool
- ROBINS-E
- Type of assessment
- simplified assessment (abstract only)
- Full formal assessment
- no
- Overall risk of bias
- low
- Rationale
Classic cohort with strong, consistent dose-response.
9. Assessment of the statistical interpretation
Very large effects consistent with causality, replicated worldwide.
10. Relevance to the specific claim
Contradicts dismissal of smoking as a cause of cancer and early death; also shows the body can recover partly after stopping a harmful exposure.
11. Independent contrary findings
12. Transferability to Germany and Europe
High.
13. Overall methodological judgement
Landmark evidence.
| Multidimensional assessment | |
|---|---|
| Authenticity of the source | verified |
| Methodological quality | high |
| Risk of bias | low |
| Precision of results | high |
| Directness | direct |
| Reproducibility | replicated |
| Consistency with the overall evidence | consistent |
| Regional transferability | high |
| Adequacy of the interpretation (by the archive) | not applicable |
14. Open questions
15. Linked fact checks
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- Cancer is the body's own plan ('a self plan'): body cells are ordered to transform because this was necessary for the person's life; it is not caused by external agents. – Studies contradicting or limiting the claim
- The body heals itself if left alone: the human body was created healthy and has an unlimited capacity for self-healing unless burdened by harmful inputs. – Studies with mixed or unclear results
- Chronic disease is mostly a cumulative reaction to what enters the body daily - contaminated food, medicines and cosmetics - not a fate that comes from outside. – Studies contradicting or limiting the claim
- Cigarettes are beneficial or at least not harmful: asked whether cigarettes are beneficial he answered 'Yes, beneficial'; elsewhere he said smoking has nothing to do with atherosclerosis and is 'not harmful at all' organically. – Studies contradicting or limiting the claim