Sleep

Naps, your untapped weapon

Greg Eder

Finding time for a nap would be great, wouldn't it? The Spanish recognised the benefits of a siesta centuries ago but who has the time for a siesta? There's too much to do, and not enough time to do it, and that's without taking a nap.

The word siesta originally derives from the Latin hora sexta "sixth hour" (counting from dawn, hence "midday rest"). Siestas are historically common well beyond Spain. Throughout the Mediterranean, Southern Europe, Mainland China, and Spanish influence, siestas are also practised in the Philippines, and many Hispanic American countries. However, the siesta is losing favour even in Spain. In 2009, one survey found that only 16% of the Spanish population still took a daily siesta.

The prevalence of Siestas can be explained as a reflection of the warmer temperatures of the regions in which they are found and heavy food intake at the midday meal, contributing to post-lunch drowsiness. In many countries that practice the siesta, the summer heat can be unbearable in the early afternoon, making a midday break at home welcome. This assumption is, however, incorrect, as we'll shortly see, so read on.

Why nap at all?

It turns out there is, in fact, a physiological basis to napping. If you have a pet dog or cat at home, you'll have likely noticed their day is interspersed with several naps. If we look at the animal kingdom, especially mammals, we find some marked similarities and some variations.

All mammals, for instance, exhibit periods of REM and NREM sleep. However, the total amount of sleep different mammals require varies hugely – from just 3 or 4 hours per day for giraffes and horses up to an impressive 22 hours for our very own koala bear. Your pet dog's or cat's sleep needs average out at 10 and 12.5 hours respectively, while the average human adult's need for sleep averages out at 8 hours.

Human sleep pattern also differs significantly from other mammals. Humans typically, consolidate sleep into one long period, while most, if not all, other mammals spread their sleep across several periods throughout the day. This consolidation of human sleep occurs even though the human circadian rhythm (the natural, internal process that regulates your sleep-wake cycle roughly every 24 hours) shows we have two periods of intense sleepiness during each 24-hour period: one around 2am-4am, and the other between 1pm-3pm. Importantly, research has found this early-afternoon sleepiness occurs regardless of the heat or having eaten.

Benefits of healthy naps

I explored the benefits and risks of sleep and sleep deprivation in my earlier blog, Sleep: we can't live without it. The health benefits of napping are also scientifically proven. Here's a look at what a quick power nap can do for you.

Improved performance.
Shorter naps (up to 30 minutes) can increase performance and make you more productive at work. Naps improve psychomotor speed, reaction time, alertness and enhance learning. Napping during the day can also improve your learning skills. Napping strengthens your focus and memory, helping you learn and retain information and help you learn new information immediately after a nap.

Better mood.
Napping during the day can improve your mood and have been linked to increased positivity and better tolerance for frustration.

Boosted energy.
Short naps boost energy levels and help get you over the afternoon slump, and help you feel less tired and irritable, especially if you lost sleep the previous night.

Lower blood pressure.
New research shows that a midday nap significantly lowers blood pressure. Midday sleep is just as effective in reducing blood pressure levels as cutting salt or alcohol consumption. On average, naps lowered blood pressure by an amount comparable to a low-dose blood pressure medication (5 mmHg).

How long should I nap?

Even a 6-minute nap can help improve recall compared to those who haven't napped at all, although those who took longer naps (25 minutes) showed even better recall.

A short afternoon nap of 20-30 minutes yields mostly S1 and S2 sleep, enhancing alertness and concentration, elevating mood, and sharpening motor skills. Research on pilots showed that a 26-minute "NASA" nap in flight (while the co-pilot flies the plane) improved performance by 34% and alertness by 54%.ii As long as you ensure your nap will be no more than 30 minutes, you could also have a coffee before you nap. Caffeine takes 20 or 30 minutes to kick in, so it should be hitting as you wake.

Unless you can stretch your nap time to 90 minutes, you're best to limit your nap to 30 minutes or less, especially if you need to spring into action when you wake. Otherwise, you risk getting into SWS which increases the likelihood of sleep inertia – that groggy feeling when you wake, often accompanied by a strong desire to keep sleeping, can last for 30 minutes or more.

However, naps of around 90 minutes usually comprise all sleep stages, including REM and deep slow-wave, which helps to clear your mind, improve memory recall, and recoup lost sleep. A long enough nap to include a full sleep cycle will also limit sleep inertia by allowing you to wake from REM sleep.

What about naps longer than 90 minutes? In general, the more full-cycles you complete during any sleep the better. When napping, instead of completing a second cycle partway, it may be better to wake up from a REM period and grab your favourite coffee. Also, if you complete a nap of two 90-minute cycles (3 hours), you run the risk of it interfering with sleep that night, especially if you had a good night's sleep the previous night.

Is some sleep better than none? Yes, most of the time, as we saw at the start of this blog, even a 6-minute nap is better than having no sleep at all. But a 20-minute nap is even better. However, when you have the time, a nap long enough to get through one sleep cycle and wake during REM will put you in a better place when you need sleep.

What about falling asleep? But, if I'm going to have a short nap, I've got to get to sleep. That's not so easy!

The military has an answer to this problem. The US Navy Pre-Flight School developed a six-week program that taught 96% pilots how to fall asleep in under two minutes, whether it be day or night and in any conditions:

  1. Get comfortable
  2. Relax your body as follows: • your face: from your forehead, cheeks, tongue, jaw, and eyes; slow your breathing (deep & slow) • your upper body: let your shoulders hang, from your neck, arms, hands, back; slow your breathing (deep & slow) • your lower body: let your legs sag, from your quads, calves, ankles to your feet; slow your breathing (deep & slow)
  3. Clear your mind for 10 seconds by imagining either: • a warm summer day lying in a park watching a few white clouds drift slowly through an otherwise clear blue sky, think about the shapes of each cloud as it drifts by – hold this image for at least 10 seconds or, • lying in a large, lush, black, velvet hammock and everywhere you look is black – hold this image for at least 10 seconds If neither of the above two imaginations works for you, repeat the words "don't think, don't think, don't think" for at least 10 seconds.

Potential Risks

It's important to note that we're talking about naps as a supplement for regular sleep to help recovery from moderate sleep deprivation. Naps should not be seen as a replacement for a total of 8 hours sleep, especially if you're going to be driving or working in a high-risk environment. When your body is sleep-deprived, you could experience microsleeps - your brain is registering S1 sleep and your eyes may not even close – which incur short lapses in consciousness that can have dangerous consequences.

Some sleep is always better than none. If you have an hour or less then 20-30 minutes is likely your best option of you risk trying to wake during SWS, which runs the risk of sleep inertia. If you have more than an hour, then 90 minutes is ideal as you can complete one cycle of sleep and wake during REM which will be easier. Any longer than 90 minutes would need to be in roughly 90-minute blocks which may then interfere with a decent night's sleep that night.


References

i. Lahl, O., Wispel, C., Willigens, B., & Pietrowsky, R. (2008). An ultra-short episode of sleep is sufficient to promote declarative memory performance. Journal of Sleep Research, 19, 3-10. DOIi: 10.1111/j.1365-2869.2008.00622.x

ii. Rosekind, M.R., Smith, R.M., Miller, D.L., Co, E.L., Webbon, L.L., Gander, P.H., & Lebacqz, J.V. (1995). Alertness Management: Strategic Naps in Operational Settings. Journal of Sleep Research, 4(2), 62-66. doi: 10.1111/j.1365-2869.1995.tb00229.x

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