Research shows that a cup of coffee can boost a nap.
Posted December 31, 2018
In many professions long shifts and high levels of stress are the norm. This is a recipe for fatigue, sleepiness, and poor judgement. Not something you want for your ER doctor, or your IT professional working late at night to keep the company online. As a result, there has been increasing recognition of the benefit of brief naps to help restore alertness and functionality when sleep is limited.
Why brief naps? We initially enter sleep through lighter stages of sleep known as stages N1 and N2. This kind of sleep relieves some sleep drive but does not do so as efficiently as deep sleep stage N3. In deep sleep there is a rapid reduction in sleep drive, much more quickly than in the lighter stages. It generally takes some time to go from alert to relaxed to drowsy to stage N1 and then stage N2 and finally deep stage N3. If a nap is timed so that it is less than about 20 minutes or so in length, it is unlikely that much stage N3 will be reached. This is important for two reasons. First, waking from deep sleep is more difficult and can leave you feeling groggy and more tired than when you started the nap. This is known as “sleep inertia” and is what is sometimes called “sleep drunkenness” – definitely not a state you would want to be in if you had to drive, be very alert, or make critical decisions. Mood could also be low and irritable – not the best for family, friends, co-workers, or clients. Second, because deep sleep rapidly relieves sleep drive it can negatively affect your ability to fall asleep later that night. It is like having a double cheeseburger on the way to a banquet. Just as that would spoil your appetite for a sumptuous dinner, a long nap would spoil your “appetite” for falling asleep at night. So a brief nap is the best of both worlds in that it helps promote alertness without interfering with nighttime sleep.
An interesting study by Brooks & Lack (2006) empirically addressed this issue. The study involved healthy young adults – 12 men and 12 women who were good sleepers. They were each randomly assigned to a series of randomly ordered naps of 5, 10, 20, and 30 minutes of sleep with a no nap control condition. In the week before the start of the study participants keep normal hours of sleep until the night before the first nap during which they were limited to only 5 hours of sleep. They were given 2 days to one week of normal length sleep before the next nap test, with sleep again limited to 5 hours on the nights before the naps. Measurements of sleep and sleep stages were made using standard sleep measures such as EEG. Certain measures of alertness, mood, and reaction time were taken at various times after the naps. Interestingly, the 5-minute nap produced few benefits above the no nap condition, while the 10-minute nap produced improvement in all areas measured such as sleepiness, fatigue, and cognitive performance. The effects of the 10-minute nap were also maintained for several hours after the nap. For the 20-minute nap performance improvements took over half an hour to emerge and did not last quite as long as for the 10-minute nap. The 30-minute nap actually resulted in a period of impaired alertness and performance in the period immediately after the nap but then resulted in improvements that lasted as long as the 10-minute nap. The EEG data indicated that either the total length of stage N2 sleep achieved or perhaps achieving some brief period of N3 delta sleep accounted for the improvements. The initial negative effect on alertness of the 30-minute nap may have been due to sleep inertia as greater delta sleep was achieved. Strange but true - the 10 minute nap wins for improvement in functioning AND its improvements last as long as those of the half hour nap. Sounds like we have a winner!
Many workers around the world have independently discovered that there is a way to take the 10-minute nap and kick it up a notch. It’s called the caffeine (or coffee) nap. This involves quickly consuming 100 to 200 mg of caffeine (or less if you are very sensitive to caffeine) in the form of a tablet, a cup of coffee or very strong tea, an energy drink, or a shot of espresso, then taking a 10 to 20 minute “power nap”. The idea is that the nap will relieve some of the pressure to sleep that has built up over a long period of wakefulness thus restoring alertness while the caffeine has time to enter the brain and have its wonderful effect of sharpening the senses and helping intensify focus. Caffeine works by antagonism of adenosine at the purine receptors in the brain resulting ultimately in increased alertness. In other words, it blocks a chemical that causes drowsiness and leaves you feeling sharper.
But does this really work? Yes, it does! While this is a technique I had been aware of for some time (and must admit to having used on more than one occasion) I was pleased to come across a nice, brief article about the coffee nap on the Vox news site by Joseph Stromberg. It gives a quick review of the relevant studies and makes some suggestions for how to most effectively use this kind of nap. Several studies reviewed there indicate that the coffee nap is more effective than either napping or drinking coffee alone.
So, the best policy remains to always get enough sleep at night and to hopefully not have to put in 12 hour or longer work days. But sometimes insufficient sleep is unavoidable and/or the shift will be extra-long, and it’s just not possible to maintain that much-needed level of alertness. That’s when you, and I, and workers around the world can take advantage of a quick dose of caffeine and a power nap. Whether you are in Sydney or Senegal, the U.K. or Uruguay, or anywhere else - a caffeine nap can be of benefit to us all. Happy New Year!
Brooks, A. & Lack, L. (2006). A Brief Afternoon Nap Following Nocturnal Sleep Restriction: Which Nap Duration is Most Recuperative? SLEEP, 29(6), p. 831 – 840.