Clinical question
Does drinking coffee affect mortality or other health outcomes in the general population?
Evidence
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Largest cohort study: 402 260 people in the United States, aged 50 to 71 years, followed for 14 years.1
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-Increased coffee consumption was associated with increased mortality, but results were confounded by smoking, inactivity, alcohol consumption, and poor diet.
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-After adjusting for confounders, coffee drinkers (compared with nondrinkers) had a significant (P < .001) decrease in overall mortality: a relative reduction of about 10% for men and 15% for women for ≥ 2 cups/d.
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-Cardiovascular (CV) events (including stroke) and accidents decreased, but cancer rates were unchanged.
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-Most coffee consumed was caffeinated, ground coffee.
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Multiple cohort studies2–6 in different populations, ages, and subgroups (eg, diabetes) had similar findings.
Context
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Evidence is from cohort studies and cannot show causation. Unfortunately, a large RCT is unlikely.
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Some studies suggest coffee is associated with reduced rates of some cancers10,11; others find no association.11–14
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Most studies find coffee is associated with fewer CV events,1,2,6,15 including stroke16; others find no association.17
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Coffee intake is also associated with a reduced risk of diabetes18 and depression.19
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Coffee in pregnancy (particularly ≥ 4 cups/d) increases risk of fetal loss.20 Pregnant women should be advised.
Bottom line
Coffee consumption is associated with no change or a small reduction in mortality in cohort studies. The evidence is not strong enough to recommend that nondrinkers start consuming coffee, but coffee drinkers can be reassured that it does not appear to result in excess harm (except in pregnancy).
Implementation
Cohort studies are subject to many biases, but confounders are particularly challenging. For example, coffee consumption is generally associated with higher-risk behaviour such as smoking, inactivity, and poor diet. Researchers might undercompensate or overcompensate when adjusting for confounders and might come to differing conclusions based on which confounders are considered.21,22 Further, Freedman et al1 did not look at preparation or additions to coffee, but calories can accumulate based on choice. A 16-oz cup of filtered black coffee has 5 calories. The same-sized latte has about 190 calories (without sugar).
Notes
Tools for Practice articles in Canadian Family Physician (CFP) are adapted from articles published on the Alberta College of Family Physicians (ACFP) website, summarizing medical evidence with a focus on topical issues and practice-modifying information. The ACFP summaries and the series in CFP are coordinated by Dr G. Michael Allan, and the summaries are co-authored by at least 1 practising family physician and are peer reviewed. Feedback is welcome and can be sent to toolsforpractice{at}cfpc.ca. Archived articles are available on the ACFP website: www.acfp.ca.
Footnotes
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Competing interests
The authors drink and enjoy coffee.
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The opinions expressed in this Tools for Practice article are those of the authors and do not necessarily mirror the perspective and policy of the Alberta College of Family Physicians.
- Copyright© the College of Family Physicians of Canada