Caffeine is the world’s most widely consumed stimulant, but new research suggests it may have unexpected effects beyond the brain and nervous system.
A study from the University of Colorado Anschutz Medical Campus, published in Haematologica, found that caffeine can reduce the quality of donated blood and make transfusions less effective, particularly in patients with certain genetic traits.
Analyzing samples from more than 13,000 blood donors, researchers discovered that higher caffeine levels in donated blood were linked to red blood cells (RBCs) that broke down more easily in storage and raised hemoglobin less effectively when transfused into patients. The effects were especially pronounced in people with common variants of the ADORA2B gene, which helps regulate RBC function under low-oxygen conditions.
“These findings suggest that something as common as your morning cup of coffee could have important implications for the quality of stored blood and how well it works when transfused into patients,” said senior author Angelo D’Alessandro, PhD, professor of biochemistry at the University of Colorado School of Medicine.
The results raise the possibility of new guidelines for blood donors. In some European countries, caffeine intake before donation is discouraged, but in the U.S. it is not. Since caffeine has a short half-life, limiting intake before giving blood could reduce its impact on stored RBCs.
Interestingly, the same processes that impair transfused blood may help explain caffeine’s well-documented performance boost in sports. Caffeine increases oxidative stress in red blood cells by blocking a protective receptor and interfering with a key antioxidant enzyme. That stress weakens stored blood but may actually trigger beneficial adaptations during exercise, where small bursts of oxidative stress are thought to drive fitness gains.
“Interestingly, we recently discovered that mice with G6PD deficiency showed improved exercise tolerance,” said co-author Travis Nemkov, PhD. “These findings illustrate how insights from transfusion medicine can inform our understanding of exercise physiology and broader aspects of human health.”
Together, the findings highlight caffeine’s double-edged role: a common dietary habit that may undermine blood storage quality, but also a factor in how the body adapts to physical stress.
This research was supported by the National Heart, Lung, and Blood Institute (NHLBI) and the National Institute of General Medical Sciences (NIGMS), with contracts and grants funding the REDS RBC Omics and REDS-IV-P programs.