Naps, caffeine and light on night shifts: what the research says

Naps, caffeine and light are tools most people already have. Used with some thought about timing, they can make a night shift more manageable. The research behind them is modest, so this article is about informed starting points, not rules, and it flags the safety catches.

Should you nap before a night shift?

The American Academy of Sleep Medicine (AASM) guideline on shift work disorder, published so far as a draft for public comment and a conference abstract, suggests a nap before the night shift for adults with excessive sleepiness. It is a conditional recommendation based on very low certainty evidence ^{[1, 2]}.

Some of the studies behind it:

• In a laboratory study of 68 healthy volunteers, napping, caffeine and the two together each improved alertness and performance during simulated night shifts, and the combination did best. In a field study of 53 shift workers, nap plus caffeine improved performance and reduced sleepiness on night shifts ^[3].
• A systematic review of 13 small studies found that napping during a night shift generally reduced sleepiness and improved performance, but none looked at actual workplace safety outcomes ^[4].

What is sleep inertia, and why does it matter?

Sleep inertia is the groggy, slowed-down feeling right after waking up. It can temporarily make thinking and reaction time worse, and it is stronger after sleep loss and at some times of day ^[6]. In a laboratory study of 21 people, a 10-minute nap before a simulated drive home after a night shift produced measurable sleep inertia on a vigilance test right after waking, although simulated driving performance did not differ from the no-nap group ^[5].

The AASM says to allow enough time for sleep inertia to clear before driving or doing other safety-sensitive tasks ^{[1, 2]}.

When should you stop caffeine?

Caffeine reduces sleepiness during the shift, and the AASM suggests it for adults with shift work disorder and excessive sleepiness, with the same very low certainty rating. Its guideline also warns that caffeine close to bedtime can disrupt sleep onset and quality ^{[1, 2]}.

How close is too close? In a home-based study, a large dose of caffeine (400 mg) taken 6 hours before habitual bedtime still reduced total sleep time compared with placebo, and doses at bedtime and 3 hours before had significant effects too ^[7]. The lesson is about your bedtime, not the clock on the wall: if your bedtime is 9 a.m., the usual advice to avoid coffee after lunch does not apply. The principle is to stop well ahead of your own sleep; caffeine and sleep covers how long it lasts in the body.

One more caution from the research: for people sleeping normally, caffeine often just restores performance that sleepiness has degraded, and regular daily intake is associated with disturbed sleep and daytime sleepiness ^[8].

What does light do on night shift?

Light is the strongest signal your body clock reads. The AASM suggests bright light during the night shift for sleepiness ^{[1, 2]}. Whether light moves the clock earlier or later depends on its timing relative to your body's own rhythm. In a laboratory study, light before the body's temperature low point delayed the clock and light after it advanced the clock ^[9].

The trip home matters too. In one study of night-shift nurses, those who wore dark goggles on the morning commute (together with bright light on shift and a stable daytime sleep schedule) slept longer than the comparison group ^[10]. The AASM guideline lists reduced-light glasses in the morning as one option for people with a fixed night schedule, and its draft notes there may be risks to driving while wearing them because of reduced alertness ^[1].

For people who rotate, the guideline says shifting the clock is not a realistic goal, so the clock-shifting side of light is not expected to help ^{[1, 2]}.

What about meals?

The AASM suggests eating a snack, or not eating, rather than a full meal during the night shift (conditional, low certainty) ^[1].

A word on melatonin

Melatonin comes up in the AASM guideline as a suggestion for daytime sleep trouble after night shifts. It also carries a warning: melatonin can temporarily increase sleepiness and raise accident risk, so time is needed before driving or other safety-sensitive tasks ^{[1, 2]}. Whether to take melatonin, how much and when are decisions for you and your doctor. This article does not give doses of melatonin. It does not give doses of prescription sleep or wakefulness medicines either. For what the wider research says, see melatonin: what it can and cannot do.

Where is the evidence thin?

• The AASM recommendations above are conditional and most rest on low or very low certainty evidence ^[1].
• Much of the napping and caffeine research was done in laboratories or small field samples ^{[3, 4]}.
• None of the napping studies in the 2014 review measured accidents or injuries ^[4].

Which tools fit you depends on whether your schedule is fixed or rotating; see rotating shifts and sleep. If the problem is sleeping after the shift rather than staying awake during it, the guideline also suggests CBT-I (cognitive behavioural therapy for insomnia) ^{[1, 2]}, and anchor sleep is one idea for keeping some of your sleep at a consistent time. If your sleepiness or insomnia has lasted for months, it may be time to see a doctor.