Suppression of sleepiness in drivers: combination of caffeine with a short nap.
Level 3 - non-randomized controlled study
Controlled trial without explicit mention of randomization in the abstract
PubMed 9401427 · doi:10.1111/j.1469-8986.1997.tb02148.x
What was done
Twelve sleepy participants completed a 2-hour continuous, monotonous afternoon drive in a car simulator following a 30-minute break. The study compared a combined treatment (200 mg caffeine plus a short nap of under 15 minutes) against 200 mg caffeine alone and placebo. Outcomes measured included driving incidents, subjective sleepiness, and electroencephalographic (EEG) indicators of sleepiness.
What was found
Placebo drives demonstrated a mid-afternoon peak across driving incidents, subjective sleepiness, and EEG measures. Caffeine alone significantly reduced this peak, resulting in driving incidents at 34% of placebo levels. The combination of caffeine and a short nap eliminated the mid-afternoon peak, reducing driving incidents to 9% of placebo levels. Naps characterized by nonsleep dozing remained effective.
Why it matters
Combining caffeine intake with a brief nap during a break provides a stronger countermeasure against afternoon sleepiness and simulated driving impairment than caffeine alone.
Limits
The sample size was very small (n = 12), and the study used a driving simulator rather than real-world on-road driving. The abstract does not report exact variance or confidence intervals, participant demographics, blinding procedures, or whether conditions were randomized.
Cited by
- supports Taking a 25-minute nap immediately after drinking black coffee allows sleep to clear brain adenosine while caffeine binds to the receptor, providing boosted alertness for 4 hours.