Researchers have proven that coffee is good for the heart, but people will need to drink at least for cups of the beverage to unlock its benefits.

The caffeine in coffee, apparently, could do more than just wake people up. Coffee can actually protect the heart, according to a study carried out by a team of researchers from Germany.

Benefits Of Coffee: Protects The Heart

"We've disproved what doctors have told your grandma: Don't drink coffee if you have a heart problem," Dr. Joachim Altschmied and Dr. Judith Haendeler told Inverse.

Altschmied and Haendeler are molecular biologists from the University of Dusseldorf, and are coauthors of a study published on the PLOS Biology journal that demonstrated the health benefits of coffee.

The researchers studied caffeinated laboratory mice and human tissue dosed with caffeine. They discovered that the stimulant may improve how cells inside the blood vessels work, by rejuvenating some proteins inside older adult cells to make them resemble younger cells.

However, for people to start experiencing the health benefits of coffee in protecting the heart, they will have to drink a "physiologically relevant amount," which is at least four cups.

"When you drink four to five cups of espresso," Altschmied said to Business Insider, "that seems to improve the function of the powerhouses of our cells, and therefore seems to be protective."

Several studies have debunked the belief that coffee is bad for the heart, including research published in in April that said drinking coffee does not lead to abnormal heart rhythms. Coffee has been determined to lower the risk for heart attacks, strokes, and diabetes.

The new research, meanwhile, finally explains why coffee is able to provide these health benefits. Caffeine pushes a protein named p27 into the mitochondria of cells, improving their performance.

Altschmied, however, warned that drinking four cups of coffee alone should not replace all the other healthy activities of people, such as exercising and eating healthy.

Coffee And Cancer

Coffee has been proven to be good for the heart, but the beverage's link to cancer is still under debate.

In May, coffee sold in California started carrying cancer warning labels. All coffee companies, from as big as Starbucks to as small as corner cafes, are required to comply with the ruling, which is based on the presence of the potentially cancerous byproduct acrylamide in the coffee roasting process.

Cancer experts, however, have refuted the warning. They claim that no link has been established between drinking coffee and developing cancer.