Using caffeine no longer improves performance or alertness after three consecutive nights of sleep restriction to 5 hours per night, a new study finds.
Relative to the placebo, the results showed that caffeine improved Psychomotor Vigilance Task (PVT) performance during the first two days, but then lost significant improvement in the last three days of restricted sleep. The PVT is a reaction-time, sustained-attention test that looks at the speed with which one responds to visual stimuli. It is understood that sleep deprivation is correlated with decreased alertness, declined cognitive functioning, decreased psycho-motor skills, slower ability to solve problems, and increased rate of responding falsely. The PVT helps determine if these problems are significant.
Lead author and research scientist at Walter Reed Army Institute of Research, Tracy Jill Doty, PhD, noted that it was surprising the performance advantage of caffeine given at 200 mg twice daily was no longer useful after three nights of restricted sleep. The results are important because caffeine is so widely used to enhance performance and alertness after a few nights of restless or restricted sleep. This study shows us that caffeine is no longer a helpful stimulant in cases of performance decline after several days of sleep restriction.
There were 48 healthy individuals part of the study group. It was a placebo-controlled double blind study. They were restricted to five hours of time in bed for a total of five days. This does not mean sleep, but time spent in bed. The participants were given either a placebo or 200 mg of caffeine twice a day. During these five days, a cognitive task battery was administered every hour during the awake periods. This included a 10-minute PVT, the Standard Sleepiness Scale, as well as the Profile of Mood States. Six times per day, a modified Maintenance of Wakefulness Test was also administered.
In addition to the above, another study found that sleep restriction on a chronic basis negatively affected the performance of athletes.
These results indicated the sleep restriction led to submaximal exercise by 3.9% due to decreased energy expenditure. It also showed that aerobic power decreased 2.9%, and time up to exhaustion decreased by 37 seconds, or 10.7%. After sleep restriction, submaximal heart rate, peak heart rate, and PVT response speed were also decreased.
Cheri Mah, MS, lead investigator and Translational Research Fellow at the University of California in San Francisco, noted that this study is unique because the researchers simultaneously looked at the relationship between physical performance, cognitive function, physiology, and sleep together. She noted that in order to understand the response of sleep interventions on athletic performance, future studies will be needed to understand the body’s physiologic response to restricted sleep and sleep extension.
This randomized cross-over study analyzed 12 elite male cyclists who were otherwise healthy. They restricted sleep for three days to four hours each night, or they were asked to extend their sleep to 10 hours a night for two weeks. All of the participants completed a baseline week of regular sleep, followed by two weeks of washout between the interventions. Pre and post intervention, outcome measures included a 1-minute incremental maximal exercise test, a maximal time to exhaustion test, a PVT, and a 20-minute submamixal test.
Both studies and abstracts will be presented in Denver at SLEEP 2016, which is the 30th Anniversary Meeting of the Associated Professional Sleep Societies, LLC.
Author: Rachael Herman is a professional writer with an extensive background in medical writing, research, and language development. Her hobbies include hiking in the Rockies, cooking, and reading.