Coffee before bed can trigger impulsive behavior, especially in women
A team of biologists from the University of Texas at El Paso found that drinking coffee at night can increase impulsivity, with this effect being particularly pronounced in women. A study on fruit flies showed that nocturnal caffeine consumption hinders behavioral control and promotes risky behavior. The researchers warn that these findings may have implications for shift workers who drink coffee late in the day.
Caffeine is the most commonly consumed psychoactive substance in the world, with approximately 85% of American adults using it regularly. Researchers from the University of Texas at El Paso decided to investigate how its consumption at different times of day affects the ability to control behavior.
“Given the popularity of caffeine, we wanted to see if additional factors might influence its effect on behavioral control,” explains Dr. Paul Sabandal, co-author of the study.
The researchers used fruit flies ( Drosophila melanogaster ), which—thanks to their genetic and neurobiological similarities—are a valued model for behavioral studies. The insects were given varying doses of caffeine at different times of day and then tested for their response to a strong airflow—a stimulus that typically causes a cessation of movement.
It turned out that flies fed caffeine at night had difficulty inhibiting movement and reacted more impulsively, "recklessly" flying despite the unpleasant stimulus.
“We observed that insects after a night of caffeine were less able to inhibit movement, which reflected impulsive behavior,” says Dr. Erick Saldes, co-author of the study.
Interestingly, the same effect did not occur when caffeine was administered during the day.
The team also found that female flies responded more strongly to nighttime caffeine than males, despite having similar concentrations of the substance in their bodies.
– “Flies do not have human hormones such as estrogen, which suggests that other genetic or physiological factors are responsible for this difference,” emphasizes Prof. Kyung An Han.
The study's authors note that the results may be relevant to night workers, such as medical and military personnel, who rely on coffee to stay alert. Women, in particular, may be more susceptible to the negative effects of nighttime caffeine consumption on behavioral control and impulsivity.
The work was conducted in Professor Han's laboratory at UTEP, which studies the neurobiological basis of behavioral plasticity—including learning, memory, addiction, and gene-environment interactions associated with neurodegenerative diseases. The researchers plan further experiments to better understand the mechanisms behind this phenomenon.
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