Study leader Dr. Masato Tsutsui, a cardiologist and professor in the pharmacology department at the University of the Ryukyus in Okinawa, Japan, said the study involved 27 healthy adults. Researchers said they found drinking a cup of caffeinated coffee significantly improved blood flow in a finger, which is a measure of how well the inner lining of the body's smaller blood vessels work.
Specifically, participants who drank a cup of caffeinated coffee had a 30 percent increase in blood flow over 75 minutes compared to those who drank decaffeinated coffee, Tsutsui said in a statement.
Compared to decaffeinated coffee, caffeinated coffee slightly raised participants' blood pressure and improved vessel inner lining function, while heart rate levels were the same for the two groups.
"This gives us a clue about how coffee may help improve cardiovascular health," Tsutsui said.
It is unclear how caffeine works to improve small blood vessel function, but Tsutsui suggested caffeine might help open blood vessels and reduce inflammation.
"If we know how the positive effects of coffee work, it could lead to a new treatment strategy for cardiovascular disease in the future," Tsutsui said.
Previous studies showed drinking coffee was linked to lower risk of dying from heart disease and stroke, and high doses of caffeine might improve the function of larger arteries.
The findings were presented at the American Heart Association's Scientific Sessions in Dallas.