Coffee drinkers—regardless of the amount or type of coffee they consumed—were less likely to die over a 10-year period than non-coffee drinkers, according to a new study published Monday in JAMA Internal Medicine, although some experts expressed skepticism about the study's findings.
For the study, researchers from the National Cancer Institute used data on nearly 500,000 men and women from the United Kingdom ages 40 to 69 who had participated in the U.K. Biobank, a large genetic study in Britain.
Participants filled out questionnaires about their daily coffee consumption, exercise, and other habits, and they also underwent a physical exam and blood tests. Of the 498,134 participants, 154,000 drank two to three cups of coffee each day, while 10,000 drank at least eight cups each day.
After a 10-year follow up period, the researchers found that coffee drinkers were about 10% to 15% less likely to die than non-coffee drinkers. This was true for consumers of both caffeinated and decaffeinated coffee—and regardless of whether an individual was a fast or slow metabolizer of coffee.
According to the researchers, previous studies have suggested that the variants in a specific gene "may alter associations of coffee drinking with cardiovascular-related outcomes, with slower caffeine metabolizers having higher risk of developing hypertension (high blood pressure) or having a myocardial infarction (heart attack) relative to their non-drinking counterparts, whereas faster caffeine metabolizers who drink coffee are at no or lower risk of these outcomes."
However, the researchers found no extra risk for any genetic variant.
It's not exactly clear why drinking coffee can lead to a longer life, but lead researcher Erikka Loftfield noted that coffee contains more than 1,000 chemical compounds, including antioxidants that help protect cells from damage.
Walter Willett of the Harvard School of Public Health said the nutrients and chemicals in coffee beans may be "working together to have some of these benefits." Christopher Gardner, director of nutrition studies at the Stanford Prevention Research Center, said that coffee contains "a number of polyphenol-like, antioxidant-rich compounds," adding that significant evidence supports the idea that coffee can be part of a healthy diet.
However F. Perry Wilson, as assistant professor of medicine at the Yale School of Medicine, expressed skepticism of the study's findings. Wilson noted that the study authors suggested that, because fast and slow metabolizers of caffeine experienced similar mortality improvements after drinking coffee, any mortality benefit must come from "non-caffeine constituents" of coffee.
But Wilson argued, "Caffeine is a drug that has significant, measurable biological effects. The other compounds in coffee, if they do anything, have subtle, difficult-to-measure effects. But now we're being asked to assume that the effect of caffeine on mortality is essentially a wash, allowing these other subtle effects to be unmasked."
Wilson likened the study to mixing cocaine with vitamin C and attempting to measure how people respond to the Vitamin C. "The active ingredient is just going to overshadow everything else," he writes.
Ultimately, Wilson writes that he believes "coffee is in the same camp as red wine: the observed benefits are likely due more to the type of person who drinks it than what's actually in the drink." He concludes, "In my opinion, if it's not the caffeine, it's not the coffee at all" (Tanner, AP/Sacramento Bee, 7/2; Aubrey, "The Salt," NPR, 7/2; Fox, NBC News, 7/2; Wilson, "The Methods Man," MedPage Today, 7/2).
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