If you can't get through the day without a dose of caffeine, you are not alone. Going by latest data, the number of Americans enjoying a daily cup of coffee is at its highest level since 2012.

But how many cups of coffee should you drink in a day? Researchers from Germany decided to find the ideal amount of caffeine that could benefit heart health.

The study titled "CDKN1B/p27 is localized in mitochondria and improves respiration-dependent processes in the cardiovascular system — New mode of action for caffeine" was published in the journal PLOS Biology on June 21.

"The old idea that you shouldn’t drink coffee if you have heart problems is clearly not the case anymore," said researcher Joachim Altschmied of Heinrich Heine-University in Düesseldorf.

The research team studied how caffeine affected mice and cells cultured from humans. They paid particular attention to a protein known as p27, which plays an important role in converting glucose into energy inside our cells.

For ten days, the mice consumed caffeine (equivalent to four cups of coffee) on a daily basis. In the heart cells, the caffeine seemed to increase the amount of p27 in their mitochondria. This helped them produce more energy and recover faster from damage. 

Upon inducing heart attacks, the mice without p27 were more likely to die compared to mice with p27 which exhibited better chances of survival. As a result, four cups of coffee was said to have a protective effect on the heart muscles, speeding up the process of repair and recovery.

While some believe the beverage may not be all that good for us, these findings add to the growing list of potential health benefits linked to coffee in recent years. 

Most recently, a 2018 review of literature by Australia researchers also found heart health benefits associated with drinking three cups of coffee. Listing anti-arrhythmic properties and improved heart function, the findings indicated that 300 milligrams of caffeine per day could be safe for arrhythmic patients.

But simply chugging down coffee is not going to help, cautioned Judith Haendeler, one of the lead researchers of the new study. "If you hear about this study and decide to drink coffee but you do nothing else — no exercise, no proper diet — then, of course, this will not work," she said. 

Moreover, these findings need to be replicated in human studies as mice hearts behave quite differently from ours, according to Greg Dusting, a professorial research fellow at the University of Melbourne, Australia. He also advised people to be mindful of their caffeine consumption.

Caffeine is ultimately a stimulant, and at high doses, it may be the wrong kind of stimulant for those at risk of heart attack or have just had one, he said. "The potentially beneficial effects of caffeine on the arteries of the heart are interesting – but not really proven to help much in the long term."