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Decaf shows the same heart benefits
What studies show
Population studies find that people who drink three cups of coffee a day are less likely to die ten years later. Any single study carries little weight on its own. A real finding needs the whole literature and confirmatory studies behind it.
Caffeine
Coffee improves sports performance by about one percent, which won't change a treadmill run but does give a bit of focus. The caffeine is a drug whose dose matters: some people get the shakes, can't sleep, or suffer neurotoxic effects if they have too much, and a genetic problem can make it hard to process.
Beyond caffeine
The benefits come from the many ingredients in the fermented bean, including polyphenols, and the same goes for green tea. Coffee is allowed in a fast because black coffee doesn't cause a sugar spike.
What did the big coffee studies find?
In a 2018 paper in JAMA Internal Medicine, Erikka Loftfield and colleagues at the US National Cancer Institute analyzed about 500,000 participants in the UK Biobank. Ground, instant, and decaffeinated coffee were each linked to lower mortality over about ten years compared with no coffee. Because people chose their own coffee habits, the study shows association only. The lowest risk appeared at two to three cups a day.
What in coffee beans might act on the body?
Chlorogenic acids, a group of polyphenols, make up as much as 10 percent of a green coffee bean by weight, and roasting breaks down part of them. Roasting also forms brown compounds called melanoidins, which gut microbes can ferment. Gut bacteria convert chlorogenic acid into smaller molecules that the body then absorbs.
How do genes change how people process caffeine?
The liver enzyme CYP1A2 breaks down most caffeine, and variants in its gene make some people fast metabolizers and others slow. In a 2006 study in JAMA, Marilyn Cornelis and colleagues studied coffee drinkers in Costa Rica. Among slow metabolizers, drinking several cups a day was linked to a higher risk of heart attack, while fast metabolizers who drank moderate amounts showed a lower risk.
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