UTEP study: Drinking coffee at night increases impulsive behavior

“Under normal circumstances, flies stop moving when exposed to strong airflow,” said Saldes, now a science research specialist at the University of Illinois College of Medicine Peoria and a former doctoral student at UTEP. “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.”

Interestingly, caffeine consumed by the flies during the daytime did not lead to the same reckless flying, the team said.

The team also discovered notable sex differences. Despite having comparable levels of caffeine in the body, females exhibited significantly greater caffeine-induced impulsivity than males.

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

The team warns that the findings could have negative implications for shift workers, health care and military personnel who consume coffee at night, particularly females.

This study was conducted in Han’s lab within UTEP’s Department of Biological Sciences. The lab focuses on the neurobiological basis of behavioral plasticity including learning, memory and addiction as well as gene-by-environment interactions relevant to Alzheimer’s disease and related dementia.

Reference:

Saldes, Erick Benjamin et al. Nighttime caffeine intake increases motor impulsivity, iScience, DOI: 10.1016/j.isci.2025.113197