When you drink a cup of coffee in the morning, you're not only waking up your mind, but your small blood vessels too.
A new study looked at the way caffeinated coffee affects how well small blood vessels work. Participants drank either caffeinated or decaffeinated coffee, and researchers observed their blood flow afterward.
They found that caffeinated coffee led to a significant increase in blood flow in the finger, an area dense with small blood vessels.
The researchers suggested that coffee's effects on small blood vessels may partially explain why the beverage has been linked to healthier hearts in previous studies.
Masato Tsutsui, MD, PhD, of the Department of Pharmacology in the University of the Ryukyus, led the study to see how coffee affected blood flow.
According to the authors of the study, coffee is the most widely consumed beverage in the world. It naturally contains caffeine, a stimulant.
The researchers referenced previous studies which have shown that coffee consumption is linked to reduced heart disease risks. However, no one had previously studied the effects of coffee on small blood vessels like capillaries that carry blood through the body.
To test whether coffee affected the health of small blood vessels, the researchers created a controlled trial in which 27 healthy participants consumed a cup of either caffeinated or decaffeinated coffee.
After drinking the coffee, researchers measured blood flow in a finger, which contains a significant number of small blood vessels. This procedure was repeated two or more days later.
The researchers found that caffeinated coffee significantly enhanced the blood flow in the finger — an index of small blood vessel function — compared to decaffeinated coffee.
Specifically, people who drank caffeinated coffee experienced a 30 percent increase in blood flow over 75 minutes of observation compared to those who had a cup of decaf.
After drinking the caffeinated coffee, blood pressure was briefly elevated. No significant difference in heart rate was found in people who drank caffeinated versus decaffeinated coffee.
The researchers concluded that caffeinated coffee increased the function of small blood cells in healthy individuals.
The authors of the study suggested that this finding could explain why coffee has been linked to positive heart health outcomes in other studies.
"This is not the first study to suggest that drinking coffee may have beneficial effects on the cardiovascular system," said Jeffrey Schussler, MD, an interventional cardiologist on the medical staff at Baylor Heart and Vascular Hospital and Baylor University Medical Center at Dallas.
"I warn patients with palpitations (skipped beats) that caffeine can make this worse. However, this is rarely dangerous," said Dr. Schussler. "I don't think that I would suggest starting a coffee habit as a heart treatment, but for my patients who drink coffee I tell them they are welcome to drink it if they like it."
The study was presented at the American Heart Association Scientific Sessions on November 20.
The research was funded in part by the All Japan Coffee Association. The researchers disclosed no conflicts of interest.