How we rate
“Strong” = several concordant meta-analyses or systematic reviews. “Moderate” = one synthesis, or several controlled trials. “Limited” = early trials only. The rating is about the quality of the studies, not about how useful the supplement is.
Coffee
In large cohorts, 3 to 4 cups a day are associated with about 17% fewer deaths and less type 2 diabetes. In trials, unfiltered coffee raises cholesterol, while filtered coffee raises it very little. During pregnancy, caffeine is linked to more miscarriages.
Benefits
- Mortality: compared to zero cups, 3 to 4 cups a day are associated with 17% fewer all-cause deaths and 19% fewer cardiovascular deaths in a review of 201 meta-analyses; out of 21 cohorts (nearly one million people), the largest decrease is 16% at 4 cups.
- Plateau: in a meta-analysis by factors, the decrease in deaths plateaus around 3.5 cups a day; drinking more was not associated with fewer deaths, and the link held with or without caffeine.
- Heart: out of 36 cohorts (1.28 million people), the lowest cardiovascular risk is observed between 3 and 5 cups a day, and high consumption was not associated with higher risk.
- Type 2 diabetes: out of 28 cohorts (1.1 million people), the risk decreases with each cup, from 8% at 1 cup a day to 33% at 6 cups; decaf as well (−6% per cup, compared to −9% for caffeinated coffee).
- Liver: drinking a lot of coffee is associated with half as many liver cancers (relative risk of 0.50) and 65% fewer chronic liver diseases; each cup per day is associated with 15% and 26% lower risk, respectively.
- Mood: out of 12 studies and 346,913 people, the heaviest coffee drinkers had a 24% lower risk of depression, with a maximum effect around 400 mL per day.
- HDL and inflammation: in a trial, 8 cups a day versus zero increased HDL by 7% and adiponectin by 6%, and decreased interleukin-18 by 8%.
Precautions
Pregnancy: each 100 mg of caffeine per day (about one cup) is associated with a 7% higher risk of miscarriage, and 700 mg or more with 72% higher; high consumption is also linked to lower birth weights. Cholesterol: in 12 trials (1,017 people), 45 days of coffee raised total cholesterol by 8.1 mg/dL, mostly with unfiltered or caffeinated coffee and in people who already have too much cholesterol. Boiled or plunger coffee: in three volunteers, purified cafestol and kahweol raised cholesterol by 66 mg/dL in 6 weeks, and infusions containing them also raised triglycerides and a liver enzyme (ALT). Homocysteine: one litre of unfiltered coffee per day for two weeks increased it by 10%. Hypertension: in hypertensive individuals, 200 to 300 mg of caffeine raise blood pressure by 8.1 mmHg (systolic) and 5.7 mmHg (diastolic) for at least 3 hours; after two weeks of coffee, however, no increase. Sleep: caffeine reduces sleep duration and efficiency, and perceived quality. Fractures: the umbrella review finds a link between coffee and fractures in women, not in men. Limits: the harmful links mostly disappear once smoking is properly accounted for, except during pregnancy; and the favourable links also come from observational studies. In trials, 8 weeks of coffee changed neither glucose tolerance nor insulin sensitivity, and coffee low in caffeine and diterpenes changed neither lipids nor vessel function. Memory: out of 11 cohorts (29,155 people), coffee was not associated with less cognitive decline or dementia in general. Cancer: in the meta-analysis of 21 cohorts, coffee was not linked to cancer mortality. The link with deaths is clearer in Europe and Asia than in the United States.
Recommended dosage
3 to 4 cups a day, the quantity linked to the largest risk reduction in cohorts; up to 8 cups a day tested in a trial.
How to take it
- What these figures are worth: almost everything comes from observational cohorts; the 2017 umbrella review calls for true randomised trials to find out if coffee is the cause.
- Quantity: 3 to 4 cups a day for the largest decrease in deaths; beyond 3.5 cups, no further gain.
- Filtered rather than boiled: in trials, filtered coffee raises cholesterol very little, whereas unfiltered coffee raises total cholesterol and LDL; cafestol, present in boiled coffee, is at least partly responsible for this.
- Decaffeinated: it is also associated with less type 2 diabetes, and the link with deaths held regardless of caffeine content.
- In the evening: caffeine lengthens the time it takes to fall asleep and shortens sleep, all the more so as the dose is high and intake is late; older people are more sensitive to it. No study in this factsheet sets a cut-off time.
- Blood pressure: in 18 trials, coffee increased systolic blood pressure by 1.22 mmHg on average, clearly less than caffeine alone (+4.16 mmHg).
Did you know?
What raises cholesterol in boiled coffee are two of its fats: in three volunteers, purified cafestol and kahweol increased it by 66 mg/dL in 6 weeks. Filtered coffee, on the other hand, raises it very little in trials.
What the studies say
This updated meta-analysis, based on more than 3.8 million subjects, examined the relationship between coffee consumption and mortality. It found non-linear inverse associations for all-cause, cardiovascular, and cancer mortality. Moderate coffee consumption, typically between 2 and 4 cups per day, was associated with a reduction in mortality risks. This inverse association for all-cause mortality was consistent regardless of age, overweight, alcohol consumption, smoking status, and the caffeine content of the coffee.
Kim Y, Je Y, Giovannucci E. — European journal of epidemiology (2019) — View the source study
For information only: not a substitute for medical advice. Dietary supplements are not a replacement for a varied, balanced diet. Learn more