A study by Japanese researchers offers new evidence that coffee boosts the function of small blood vessels in people who are already healthy. The researchers recruited 27 young adults in their 20s to participate in the study. None of them were regular coffee drinkers, but they agreed to consume coffee for the sake of science.
On one of the days, the coffee was caffeinated. On the other day, they drank decaf. They weren’t told which was which. Neither were the researchers, who measured the volunteers’ blood pressure and blood flow after they finished their beverages. The researchers placed a probe on the tip of each volunteer’s left index finger or thumb and used a technique called laser Doppler flowmetry to measure blood flow to the digit. It works by shining a laser beam through the blood and measuring how much it is scattered by the movement of red blood cells.
For the study, the researchers interrupted blood flow to the hand for one minute. When the minute was up, they monitored how quickly the normal blood returned to the finger or thumb. It turned out that blood flow measured in the finger or thumb was 30% higher on the day they had regular coffee than on the day they had decaf. This was significant because the measurements are a proxy for how well the small blood vessels in the body are working.