Coffee can do more than just keep people awake for the day -- studies have shown that moderate amounts of caffeine, like what's in coffee, can actually protect the heart.
A new study looked at possible reasons for those beneficial effects, by studying the genes of mice.
"We wanted to do this study to show people coffee is not as bad for your heart as people thought for a long time," co-author Dr. Judith Haendeler, medical faculty at the HHU Duesseldorf and IUF-Leibniz Research Institute for Environmental Medicine, told ABC News.
But why could coffee-like caffeine levels be helpful for the heart?
Building on their previous research that showed that caffeine could help with the repair of cells lining blood vessels, called endothelial cells, researchers at the Heinrich-Heine-University and IUF-Leibniz Research Institute for Environmental Medicine in Duesseldorf, Germany, set out to explore some of the reasons caffeine consumption may be associated with heart protection.
"It is important to know what happens on a molecular and cellular level with certain amounts of coffee to know the potential protectant effects of coffee," co-author Dr. Joachim Altschmied, laboratory head for the IUF-Leibniz Research Institute for Environmental Medicine, told ABC News.
The study was conducted on mice and cells cultured from humans, particularly looking at the role of caffeine on a cell-cycle inhibitor gene known as mitochondrial p27. The study used a standard four cups of coffee per day and found that this moderate coffee consumption improved outcomes for mice with prior heart attacks.
The gene p27 has already been shown to have a role in cancer; if inactivated, p27 allows the cell cycle to continue unregulated, which leads to excessive cell proliferation and cancer. Caffeine acts on this protein, allowing cells to get more energy and more blood flow throughout the heart –- and that means fewer heart cells dying.
Mice without p27 died more often after heart attacks, while mice with p27 showed the opposite outcome. More caffeine meant more effective p27, and even better survival.
But a study in mice is several steps away from a study in humans, who might react differently to caffeine. Researchers think diet and exercise could also play a role in the relationshilp between caffeine and the gene p27.
"Our research with mice and primary human cells cannot completely mirror the exact situation of a living human being," Haendeler said. "You cannot simply adjust exercise and diet as you go along with cultured cells."
But this study gives some needed insight into why caffeine could be helpful for people at risk for cardiovascular disease -- in moderation.
"Regardless of what this research says, it is important to drink caffeine in moderation," Haendeler said. "We do not want to give false ideas about caffeine because it can be toxic in lethal doses."