Does Drinking Coffee at Night Make You More Impulsive? Study Provides Insights - Video

Drinking coffee late at night could lead to more impulsive and potentially risky behaviour-especially in women-according to a new study conducted by researchers at The University of Texas at El Paso (UTEP). Published in the journal iScience, the research found that nighttime caffeine consumption disrupts inhibition and increases impulsivity, even when caffeine levels remain the same throughout the day.

To explore how caffeine affects behaviour during different times of the day, researchers used fruit flies (Drosophila melanogaster), a widely accepted model for studying complex behaviours due to their genetic and neurological similarities to humans. The research team introduced caffeine into the flies' diets under various controlled conditions, varying the dosage, time of consumption (day vs. night), and even pairing it with sleep deprivation.

They then evaluated the flies’ responses to strong airflow—a naturally aversive stimulus—to measure impulsivity. Normally, fruit flies reduce movement when exposed to strong gusts. However, this response changed when caffeine was introduced at night.

“Under normal circumstances, flies stop moving when exposed to strong airflow,” said Erick Saldes, a science research specialist at the University of Illinois College of Medicine Peoria. “We found that flies consuming caffeine at night were less able to suppress movement, displaying impulsive behaviours such as reckless flying despite these aversive conditions,” he added.

Interestingly, the same caffeine dose consumed during the day did not cause similar behavioural changes. Even more notable was the difference between male and female flies—females showed significantly higher impulsive responses to nighttime caffeine, despite having similar caffeine levels in their bodies.

“Flies don't have human hormones like oestrogen, suggesting that other genetic or physiological factors are driving the heightened sensitivity in females,” explained Professor Kyung-An Han of UTEP’s Department of Biological Sciences.

The findings may have real-world consequences for individuals who regularly consume caffeine at night, such as shift workers, healthcare professionals, and military personnel. The researchers hope that further exploration of these mechanisms will enhance understanding of how biological sex and circadian rhythms influence caffeine’s behavioural effects.

Reference: Nighttime caffeine intake increases motor impulsivity, Saldes, Erick Benjamin et al., iScience, Volume 28, Issue 8, 113197