Coffee is a complex mixture of compounds, some of which have been revealed in laboratories to have biological effects, Gunter said.
Studies have shown that certain compounds have neuroprotective and anti-inflammatory properties
that can help reduce risk for illnesses like Parkinson's disease.
In the European study, people who were drinking coffee tended to have lower levels of inflammation, healthier lipid profiles and better glucose control compared with those who weren't. It is still unclear which particular compounds provide health benefits, but Gunter said he would be interested in exploring this further.
Both studies separated smokers from nonsmokers, since smoking is known to reduce lifespan and is linked to various deceases. However, they found that coffee had inverse effects on mortality for smokers too.
"Smoking doesn't seem to blunt the effects of coffee," Gunter said. "It didn't matter whether you smoked or not. There was still a potential beneficial affect of coffee on mortality."
However, Dr. Alberto Ascherio, professor of Epidemiology and Nutrition at Harvard T.H. Chan School of Public Health, said people should be wary of this finding.
"Even if it was in some way true, it doesn't make sense to me, because by smoking, you increase your mortality several-fold. Then, if you reduce it by 10% drinking coffee, give me a break," said Ascherio, who was not involved in the study.
"I think it's a dangerous proposition because it suggests that a smoker can counteract the effects of smoking by drinking coffee, which is borderline insane."