Study: Drinking Coffee at Night May Cause Impulsive Behavior

A recent study from a team at the University of Texas at El Paso suggests drinking coffee at night may lead to more risky and impulsive decisions.

Published Aug. 15 in the journal iScience, the findings may carry implications for shift workers, healthcare professionals, military personnel or other people who regularly consume coffee during nighttime hours to maintain alertness.

The UTEP research team led by Erick Saldes, Paul Rafael Sabandal and Kyung An Han used fruit flies (Drosophila melanogaster) as their test subjects, given their remarkable genetic and neural similarities to humans.

The flies consumed caffeine under various conditions different doses, nighttime versus daytime, and in combination with sleep deprivation then were measured for impulsivity. The flies were subjected to strong airflow, a naturally unpleasant stimulus that normally causes them to stop moving.

“Flies consuming caffeine at night were less able to suppress movement, displaying impulsive behaviors such as reckless flying despite these aversive conditions,” Saldes, who is now at the University of Illinois College of Medicine Peoria, said in an announcement of the study.

The study also showed significant differences in behaviors between the sexes. Female flies showed much greater caffeine induced impulsivity than males, despite having similar levels of the stimulant in their bodies.

“Flies don’t have human hormones like estrogen, suggesting that other genetic or physiological factors are driving the heightened sensitivity in females,” UTEP Biological Sciences Professor Kyung An Han said. “Uncovering these mechanisms will help us better understand how nighttime physiology and sex specific factors modulate caffeine’s effects.”

While noting previous research suggesting that caffeine may impair fine motor control in some people, as well as research highlighting caffeine’s performance-boosting effects, the authors said the study uncovers a “previously unrecognized risk of nighttime caffeine use.”

“While most studies have focused on caffeine’s effects during daytime or on sleep loss per se, its behavioral impact following nighttime consumption remains largely unexplored, despite its widespread use among overnight shift workers,” the study states.