Is coffee drinking associated with reduced all-cause mortality?
Date of publication of the systematic review: May 2015
Design
Systematic review of 17 prospective cohort studies.
Participants
A total of 1,054,571 healthy participants (age range: 20-79 years, overall male %: not reported).
Intervention
Coffee drinking with 1-2 cups, 3-4 cups or ≥5 cups per day.
Comparator
Comparison 1: Coffee drinking with 1-2 cups per day versus not/occasional drinking;
Comparison 2: Coffee drinking with 3-4 cups per day versus not/occasional drinking;
Comparison 3: Coffee drinking with ≥5 cups per day versus not/occasional drinking.
Major Outcomes
Outcome 1: All-cause mortality.
Settings
The reviewers did not state whether the study was conducted in in-patient or out-patient settings.
Comparison    Coffee drinking with 1-2 cups per day versus not/occasional drinking
Main Results
Compared to non/occasional drinkers, people who drink 1-2 cups of coffee per day have significantly lower risk of death (pooled risk ratio (RR): 0.89, 95% CI: 0.85 to 0.93) from all causes.
Comparison 1: Coffee drinking with 1-2 cups per day versus not/occasional drinking.
Outcomes No. of studies (Total no. of participants) All-cause mortality/ No. of participants Heterogeneity test ( I2) Pooled RR (95% CI) Overall quality of evidence*
Intervention Comparator
1 17 (1,054,571) Not reported Not reported 75% 0.89 (0.85 to 0.93) Low
Keys: RR: risk ratio; CI: confidence interval.
Comparison    Coffee drinking with 3-4 cups per day versus not/occasional drinking
Main Results
Compared to non/occasional drinkers, people who drink 3-4 cups of coffee per day have significantly lower risk of death (pooled risk ratio (RR): 0.87, 95% CI: 0.83 to 0.91) from all causes.
Comparison 2: Coffee drinking with 3-4 cups per day versus not/occasional drinking.
Outcomes No. of studies (Total no. of participants) All-cause mortality/ No. of participants Heterogeneity test (I2) Pooled RR (95% CI) Overall quality of evidence*
Intervention Comparator
1 17 (1,054,571) Not reported Not reported 60% 0.87 (0.83 to 0.91) Low
Keys: RR: risk ratio; CI: confidence interval.
Comparison    Coffee drinking with ≥5 cups per day versus not/occasional drinking
Main Results
Compared to non/occasional drinkers, people who drink ≥5 cups of coffee per day have significantly lower risk of death (pooled risk ratio (RR): 0.90, 95% CI: 0.87 to 0.94) from all causes.
Comparison 3: Coffee drinking with ≥5 cups per day versus not/occasional drinking.
Outcomes No. of studies (Total no. of participants) All-cause mortality/ No. of participants Heterogeneity test (I2) Pooled RR (95% CI) Overall quality of evidence*
Intervention Comparator
1 17 (1,054,571) Not reported Not reported 19% 0.90 (0.87 to 0.94) Low
Keys: RR: risk ratio; CI: confidence interval.
Comparison    Coffee drinking with 1-2 cups per day versus not/occasional drinking
Main Results
Compared to non/occasional drinkers, people who drink 1-2 cups of coffee per day have significantly lower risk of death (pooled risk ratio (RR): 0.89, 95% CI: 0.85 to 0.93) from all causes.
Comparison 1: Coffee drinking with 1-2 cups per day versus not/occasional drinking.
Outcomes 1
No. of studies (Total no. of participants) 17 (1,054,571)
All-cause mortality/ No. of participants Intervention Not reported
Comparator Not reported
Pooled RR (95% CI) 0.89 (0.85 to 0.93)
Overall quality of evidence* Low
Keys: RR: risk ratio; CI: confidence interval.
Comparison    Coffee drinking with 3-4 cups per day versus not/occasional drinking
Main Results
Compared to non/occasional drinkers, people who drink 3-4 cups of coffee per day have significantly lower risk of death (pooled risk ratio (RR): 0.87, 95% CI: 0.83 to 0.91) from all causes.
Comparison 2: Coffee drinking with 3-4 cups per day versus not/occasional drinking.
Outcomes 1
No. of studies (Total no. of participants) 17 (1,054,571)
All-cause mortality/ No. of participants Intervention Not reported
Comparator Not reported
Pooled RR (95% CI) 0.87 (0.83 to 0.91)
Overall quality of evidence* Low
Keys: RR: risk ratio; CI: confidence interval.
Comparison    Coffee drinking with ≥5 cups per day versus not/occasional drinking
Main Results
Compared to non/occasional drinkers, people who drink ≥5 cups of coffee per day have significantly lower risk of death (pooled risk ratio (RR): 0.90, 95% CI: 0.87 to 0.94) from all causes.
Comparison 3: Coffee drinking with ≥5 cups per day versus not/occasional drinking.
Outcomes 1
No. of studies (Total no. of participants) 17 (1,054,571)
All-cause mortality/ No. of participants Intervention Not reported
Comparator Not reported
Pooled RR (95% CI) 0.90 (0.87 to 0.94)
Overall quality of evidence* Low
Keys: RR: risk ratio; CI: confidence interval.
Conclusion
Benefits
Compared to non/occasional drinker, people who drink 1-≥5 cups of coffee per day have significantly lower risk of death from all causes. For all outcome, the overall quality of evidence is low. Further research is likely to have an important impact on our confidence in this estimate of effect.
Harms
No adverse events were reported.
Link to Original Article
https://www.ncbi.nlm.nih.gov/pubmed/25089347
The synopsis is based on the following article:
Zhao Y, Wu K, Zheng J, Zuo R, Li D. Association of coffee drinking with all-cause mortality: a systematic review and meta-analysis. Public Health Nutrition. 2015 May;18(7):1282-91.


* Interpretation of quality assessment results:
• Very low: Further research is most likely to have an important impact on our confidence in this estimate of effect.
• Low: Further research is likely to have an important impact on our confidence in this estimate of effect.
• Moderate: Further research is fairly likely to have an important impact on our confidence in this estimate of effect.
• High: Further research is unlikely to have an important impact on our confidence in this estimate of effect.
• Very high: Further research is most unlikely to have an important impact on our confidence in this estimate of effect.

Details of assessment method can be found at Chung VC, Wu XY, Ziea ET, Ng BF, Wong SY, Wu JC. Assessing internal validity of clinical evidence on effectiveness of CHinese and integrative medicine: Proposed framework for a CHinese and Integrative Medicine Evidence RAting System (CHIMERAS). European Journal of Integrative Medicine. 2015 Aug 31;7(4):332-41.