498,134 grown-ups · UK

Coffee lovers, good news. Mostly!

People say: “Too much coffee is bad for you” We read the study.

What they did

Cohort study. 498,134 people. up to 10 years of follow-up (median 7 years), 2006-2016.

People were watched for years. Nobody was told what to do. A clue, not proof.

Who: UK Biobank volunteers aged 38-73 (mean 57), 54% women, recruited 2006-2010 across England, Scotland and Wales; about 5.5% of those invited took part; genetic data on 403,816

1

Almost half a million UK grown-ups joined a study.

2

Each said how many cups they drank. Just once.

3

Up to 10 years later: who was still alive?

What they found
  • 8+ cups, first lookMoredied
  • 8+ cups, smoking taken outFewerdied
The catch

Nobody was told to drink coffee.

More to know, from our read of the paper:

  • Observational cohort: association, not causation; the authors write that the results 'are based on observational data and should be interpreted with caution'
  • Coffee intake self-reported once at baseline via a touchscreen question (cups per day); no repeat measurement, no cup size, no milk/sugar data
  • Low participation (~5.5%): not representative of the UK population, with evidence of 'healthy volunteer' selection bias (stated by the authors)
  • Before adjusting for smoking etc., 8+ cups/day had HIGHER mortality (age/sex-adjusted HR 1.30, 1.17-1.45); heavy drinkers were more often current smokers. The lower-risk finding depends on statistical adjustment, so residual confounding is possible
  • Coffee-type analyses (instant, ground, decaf) only go up to a combined '6 or more cups/day' group, not 8+; instant associations were weaker than ground
The verdict

A clue. Not proof.

One thing to try
  1. Love coffee? This study gave no reason to quit.
In short

Almost half a million UK grown-ups (aged 38–73) said once how many cups of coffee they drank a day, and scientists checked who died over up to 10 years (a cohort study, UK Biobank). Coffee drinkers died a bit less often than non-drinkers, and decaf and instant showed similar links. At first, 8+ cups a day looked worse, because heavy coffee drinkers smoked more; only after taking smoking into account did 8+ cups look about 14% better than none. Nobody was told to drink coffee, so this is linked, not proven: a clue, not proof.

The video
The paper

Loftfield et al. (2018). Association of Coffee Drinking With Mortality by Genetic Variation in Caffeine Metabolism: Findings From the UK Biobank. JAMA Internal Medicine.

Design: Cohort study · prospective cohort study (linked, not proven)

DOI: 10.1001/jamainternmed.2018.2425

Goals:

Eat betterHealthy old age
How we checked

We read the abstract and the full text of this paper and checked every number on this page against it (16 facts, checked on 2026-09-27). The study design is named above. Cohort and other observational studies are described as linked, not proven. Found an error? Email theis@onestudyaday.com.

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