Study Tests a Caffeine-Nap Strategy for Drivers With Treated Sleep Apnea

A study of drivers with obstructive sleep apnea (OSA) suggests that the usual “caffeine nap” approach may need to be adjusted for people with the condition. In a driving-simulator experiment, two coffees improved alertness and reduced driving errors more than one, while adding a short nap provided only modest additional benefit.

The research, published in Scientific Reports and reported by Medical Xpress, involved 21 drivers with OSA who were receiving continuous positive airway pressure (CPAP) treatment. Participants completed simulator sessions after having their sleep restricted to four hours. Researchers compared different caffeine amounts, nap durations and combinations of caffeine and naps, monitoring brain activity, eye movements and driving behavior.

The study found no observed additional benefit from extending a nap from 15 minutes to 30 minutes. A 15-minute nap did appear to help some participants when added to two coffees, but the largest improvement in alertness came from the two-coffee condition. The researchers said the result may reflect the higher caffeine consumption observed in real-world drivers with OSA, although the study did not establish that caffeine or napping makes driving safe after inadequate sleep.

The researchers’ proposed response for a sleepy driver with OSA is to pull over safely, consume two iced coffees or another caffeine source, and take a 15-minute nap. The source material specifically mentions a 250-milliliter canned iced coffee as an option because it provides a consistent caffeine dose and can be consumed quickly. When time is limited, the guidance describes consuming two coffees without taking the nap.

The experiment also highlighted a separate concern about CPAP treatment. Participants showed signs of impaired driving after only four hours of sleep, even though that duration is commonly used as a threshold for CPAP-treatment compliance. The researchers therefore emphasized that using CPAP as prescribed does not necessarily mean someone has slept long enough to drive safely.

Professor Ashleigh Filtness of Loughborough University’s Transport Safety Research Center, who led the study, said people with treated OSA were safe to drive when alert but showed impairment after sleep restriction. The researchers encouraged people with OSA to obtain as much sleep as possible with CPAP and, if necessary, continue sleeping without CPAP rather than treating compliance alone as evidence of sufficient sleep.

The countermeasures tested are temporary and do not replace adequate sleep, according to the researchers. Loughborough’s team is working with clinicians, charities and road-safety organizations to share the findings and plans further research on napping in vehicles.