Reaching for a cup of coffee late at night to stay sharp? A new study suggests it might do more than just keep you awake; it could also make you more impulsive.
Researchers at The University of Texas at El Paso found that nighttime caffeine consumption led to riskier behavior in fruit flies, including a loss of impulse control, even when the flies weren’t sleep-deprived. The findings, published in iScience, add to growing questions about how caffeine affects the brain at different times of day and why some people may be more sensitive than others.
“Caffeine is the most widely consumed psychoactive substance in the world, with about 85% of adults in the U.S. using it regularly,” said study co-author Paul Sabandal, PhD. “Given caffeine’s popularity, we wanted to explore whether additional factors influence its impact on behavioral control.”
To do that, the team fed fruit flies caffeine at different times of day and tested their ability to respond calmly to unpleasant stimuli, in this case, bursts of strong airflow. Normally, fruit flies stop moving when they’re hit with air. But flies who had caffeine at night didn’t settle down; they kept flying, even when conditions got uncomfortable.
“We found that flies consuming caffeine at night were less able to suppress movement, displaying impulsive behaviors such as reckless flying despite these aversive conditions,” said Erick Saldes, PhD, now a researcher at the University of Illinois College of Medicine Peoria.
Interestingly, daytime caffeine didn’t have the same effect. It was specifically nighttime intake that disrupted the flies’ ability to regulate behavior, suggesting that circadian rhythms may play a role in how caffeine affects the brain.
The researchers also found notable sex differences. Female fruit flies were significantly more affected than males, despite having similar caffeine levels in their systems.
“Flies don’t have human hormones like estrogen, suggesting that other genetic or physiological factors are driving the heightened sensitivity in females,” said Kyung-An Han, PhD, professor of biological sciences at UTEP. “Uncovering these mechanisms will help us better understand how nighttime physiology and sex-specific factors modulate caffeine’s effects.”
Though the research was conducted in flies, the findings may have implications for humans, particularly for shift workers, health care professionals and military personnel who often rely on late-night caffeine to stay alert.
While more research is needed to confirm similar effects in people, the study adds to the growing body of evidence suggesting that when you consume caffeine may be just as important as how much and that individual biology may shape the way your body and brain respond.
This research was supported by the National Institutes of Health, the Brain & Behavior Research Foundation and the Orville Edward Egbert, M.D. Endowment Fund.