(WTVO/WQRF) – For years, scientists have traced a link between coffee drinking and heart health, but they weren’t sure exactly why coffee was associated with so many health benefits.

A group of German researchers thinks it has about a possible answer, and it has to do with how the cells in our blood vessels react to caffeine.

The researchers think the caffeine level required for optimal heart health is about four shots’ worth of espresso a day, though everyone’s caffeine concentrations will be a little different.

Four cups of strong coffee a day might be the recipe for a healthy heart, especially for older adults.

A team of German researchers, led by the molecular biologists Judith Haendeler and Joachim Altschmied, thinks it has discovered clues about how coffee works its caffeine-fueled magic on our heart health by studying caffeinated lab mice and dosing human tissues with caffeine. The researchers discovered how a jolt of the stimulant could improve the way cells inside our blood vessels work – essentially, by making certain proteins inside older adult cells perform more like young and nimble ones.

The study was published Thursday in the journal Plos Biology.

“When you drink four to five cups of espresso,” Alschmeid told Business Insider, “that seems to improve the function of the powerhouses of our cells, and therefore seems to be protective.”

Scientists have, for years, noticed that people who drink coffee seem to be less likely to die from all sorts of causes, including heart disease, stroke, or diabetes. Perhaps the best evidence yet for this comes from two massive studies: one of more than 400,000 people in the US by the National Institutes of Health, and another of more than 500,000 Europeans. Both studies found that regular coffee drinkers were less likely to die from any cause than people who don’t sip a daily brew.

Coffee is also associated with a whole host of other health benefits, including a lower rise of liver disease, a lower risk of developing certain kinds of cancer, lower rates of dementia and Alzheimer’s, and a reduced risk of depression. It’s also great for your heart – people who drink three to four cups a day may be 19 percent less likely to die from cardiovascular disease.

One caveat: the study wasn’t done in humans, only in human tissues and lab mice. What works in a hyper-controlled environment may not be the same as what happens when you drink a cup of Joe at home.

“If I had four cups of espresso and you had four cups of espresso, we cannot guarantee that we reach the same level in the blood,” Altschmied said.

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