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Drinking coffee — even decaffeinated coffee — may protect your liver, a large new study has found.

Researchers examined the coffee-drinking habits of 27,793 people who filled out diet questionnaires in a large national health study from 1999 to 2010. The scientists also tracked blood levels of four enzymes that indicate liver function. The study is online in Hepatology.

More than 14,000 of the subjects drank coffee. After controlling for age, sex, race, education, smoking, alcohol consumption and other factors, the researchers found that compared with people who drank no coffee, those who drank three cups a day were about 25 percent less likely to have abnormal liver enzyme levels. Among the more than 2,000 who drank only decaffeinated coffee, the results were similar.

The reason for the effect is unclear. “There are more than a thousand compounds in coffee,” said the lead author, Qian Xiao, a cancer prevention fellow at the National Cancer Institute. “There are a few candidates, but I don’t know which is responsible.”

Should those who do not drink coffee start doing so? “This is an observational study and not designed to determine cause and effect,” Dr. Xiao said. “So based on this study, I wouldn’t make any recommendations. But it is reassurance that coffee and decaf are not harmful to liver function.”