Sleep tips for the science-minded:
An evidence-based guide
© 2008 Gwen Dewar, all rights reserved
Looking for evidence-based sleep tips?
These articles review the latest relevant research in anthropology, brain science, sleep science, and pediatrics.
They include discussions of
and the best-available evidence regarding
child sleep requirements.
In addition, there are articles about
Below I provide (1) a brief introduction to the anthropology of sleep, and (2) an overview of the articles in this collection.
1. The anthropology of sleep
What's the right way to doze? Many of the sleep tips you find in popular books and
magazines are based on cultural assumptions about what constitutes good
sleep. For instance, in some Western countries, people are expected to
- go to sleep at the same time every night,
- sleep continuously through the night,
- avoid naps, and
- insist that their children sleep alone.
Viewed cross-culturally, this is an unusual set of assumptions. Add complicating factors -- like an overheated sleep space, or exposure to artificial lights
and electronic media before bedtime -- and it's clear that many people are trying to sleep in ways that differ dramatically from those of our ancestors (Worthman and Melby 2002; Jenni and O’Connor
2005; Yetish et al 2015).
If you’re struggling with sleep problems--and trying to evaluate
popular sleep advice--it's helpful to consider sleep in biological and cross-cultural perspective.
Night awakenings are normal.
Healthy people don't sleep continuously. They cycle through different stages of sleep, and experience multiple arousals during the night. Sometimes these are fleeting; in other cases, they last longer. Newborns and young babies typically awaken because they are hungry. The goal isn't to eliminate such wakings, but reduce the unwanted disruption they cause. For more information -- about what's normal in babies and children, and how to reduce nighttime disruptions -- see these sleep tips about night wakings.
Our ancestors didn't have tight schedules, or the self-sabotaging habit of "watching the clock."
Consistent bedtimes seem really important when you have to catch that bus every morning at the same time. But in pre-industrial cultures, people have more flexible schedules (Worthman and Melby
2002; Yetish et al 2015), and they may also have fewer sleep hang-ups. One of the biggest causes of insomnia is the tendency to worry about the timing of sleep and the consequences that poor sleep will have for the following
day (Ong et al
2012). Pre-industrial foraging peoples -- who can't watch the clock -- experience their share of irregular bedtimes and normal, incidental night awakenings. But these people report very low rates of sleep trouble. In fact, when anthropologists have asked about it, they faced a language barrier: The foragers didn't even have a word for "insomnia" (Yetish et al 2015)!
Our bodies evolved to use changes in lighting as cues for sleep.
Light is an important environmental cue for regulating your body's inner clock, so exposure to natural lighting conditions over the course of the day promotes drowsiness at bedtime (Wright et al 2013). Nighttime exposure to artificial light--especially the blue wavelengths of light emitted by many light bulbs and electronic screens--is particularly bad for sleep: It suppresses the brain's secretion of melatonin, the hormone that makes us feel sleepy after dark. It also delays the onset of REM, or rapid eye movement sleep, and may shorten the total duration of sleep (Holzman 2010).
How much does our modern use of artificial lighting cost us? Perhaps quite a lot. In one recent study,
researchers found that electricity had a major impact on the timing of sleep among groups of foragers indigenous to the Chaco region of Argentina.
Individuals with free access to electricity fell asleep later, and slept, on average, about
45-60 minutes less each night than those who relied exclusively on
natural light (de la Iglesia et al 2015).
Our ancestors' most pressing sleep problem was getting through the night without being threatened by predators, intruders, and other dangers.
People who slept "like logs" or
who were unfazed by mysterious night noises would have been less likely
to survive and pass on their genes. People who slept alone--without the
benefit of multiple eyes and ears to help keep watch--would have been at
a similar disadvantage. Seeking safety in numbers, our ancestors slept
For the reasons just stated, children--the most vulnerable members of the group--weren’t left to sleep alone.
And if children cried out in the night--attracting the attention of
predators--it made sense to quiet them down as soon as possible.
Implications for you and your family
This review suggests several important points.
- People don't really "sleep through the night." At best, they bounce back
and forth between various sleep stages and brief states of drowsy
- Exposure to artificial lighting can interfere with natural sleep rhythms.
- Our ancestors didn't feel pressured to fall asleep by a certain time, and, as a result, they were probably less prone to self-inflicted bouts of insomnia.
- For most of human history, being easily aroused during the night was normal and adaptive.
So was being cautious or anxious about things go bump in the night. So
was responding promptly to your child’s cries.
- Kids didn’t sleep alone. Being alone meant abandonment, injury, or death.
Does this mean we must live like Pleistocene hunter-gatherers to
sleep well? No. But it should make us question the cultural practices
and sleep tips that depart radically from the ancestral pattern. And it
offers some helpful insights for solving child sleep problems.
First, many child sleep problems aren’t pathological in the sense
of being "unnatural" or biologically abnormal. When kids suffer from
nighttime fears or resist going to bed by themselves, they may be
expressing psychologically normal, healthy responses.
Second--no matter what any sleep researcher, pediatrician, or
nosy relative might say--your urge to soothe your child to sleep is
biologically normal. Parents should keep this in mind if they feel
pressured to try tactics or sleep training programs that violate their parental instincts.
Third, many sleep problems may be caused by a poor fit between
our cultural practices and our needs. For example, Western children
often resist going to bed at night. In part, these bedtime battles may
be caused by the practice of solitary sleeping--a Western custom that
may trigger separation anxiety in young children.
The bottom line?
Before you take any sleep advice to heart--or let someone
convince you that your family’s sleep practices are "wrong"--you should
exercise a healthy skepticism.
An anthropological approach to sleep can help us discover which
aspects of sleep are essential and which aspects are subject to cultural
variation. The articles in these pages will help you decide which sleep
solutions are best for you and your children.
2. Evidence-based sleep tips
Western sleep practices may be poorly matched to the needs of some
kids and adults (Jenni and O’Connor 2005). For babies, the fit may be
even worse. In particular, Western cultural expectations about solitary
sleeping and “sleeping through the night" may cause families
But whether you accept or reject Western sleep practices, there
is much you can do to minimize sleep problems during infancy. For
information about sleep in infants--including sleep requirements, sleep
patterns, and a variety of practical sleep tips--see this
collection of articles on baby sleep.
How much sleep does your child need?
How can you tell if your child is sleeping enough? When I first began
researching sleep requirements, I assumed that those authoritative
charts we see published everywhere--the ones telling us that the average
newborn needs 16 hours of sleep, for example--were based on
scientifically-established, physiological needs.
I was wrong. It turns out that no one really knows how much sleep
children need for optimal health and growth. And kids, like adults, may
vary considerably in their individual requirements.
So if you really want to understand your child’s personal sleep
needs, you need to go beyond the published sleep charts. In this article
I review the latest scientific evidence and discuss ways to apply this information to your family.
In addition, my article about
outlines the symptoms and signs of insufficient sleep in babies, children, and adults.
Why can't your child sleep?
According to Western sleep studies, "bedtime resistance" and frequent
night wakings are among the most common sleep complaints that parents
report to their pediatricians (Mindell et al 2006).
What causes kids to resist bedtime? Or awaken frequently at
These sleep problems may stem from a variety of causes, and it’s
important to understand why your child can’t sleep before you attempt
In many cases, kids may suffer from nocturnal fears and
anxieties. For more information, see my article on
nighttime fears in children.
It explores the evolutionary basis for nighttime fears and discusses why
kids are biologically unprepared to handle nighttime fears on their
own. It also offers practical advice for helping your child overcome her
For other sleep tips, see my articles on
nightmares and night terrors.
The article on bedtime problems includes a trouble-shooting checklist to
help you identify why your child may have trouble falling asleep.
The article on night wakings reviews the science of disrupted
sleep, and includes practical sleep tips for improving the quality of
your child’s sleep.
The article on nightmares and night terrors helps you distinguish
between these two conditions, and offers sleep tips for treating them.
The Ferber method--also called “graduated extinction"--is one of the
most famous sleep training programs. It is also one of the most
controversial, primarily because it involves a degree of “cry it
out." For a detailed account of graduated extinction--including
arguments for and against its use--see this article on the
As I note in this article, the Ferber method appears to be very
effective in some respects. However, it's clearly inappropriate for some
children, and despite headlines to the contrary, the jury is still out
regarding the possibility of negative side effects.
For information about alternatives to the Ferber method, see this article on
“no cry" sleep training.
References: Family sleep tips and topics
Ekirch AR. 2005. At Day's Close: Night in Times Past. New York: WW Norton.
de la Iglesia HO, Fernández-Duque E, Golombek DA, Lanza N, Duffy JF,
Czeisler CA, Valeggia CR. 2015. Access to Electric Light Is Associated
with Shorter Sleep Duration in a Traditionally Hunter-Gatherer
J Biol Rhythms. 30(4):342-50.
Holzman DC. 2010. What's in a color? The unique human health effect of blue light. Environ Health Perspect. 118(1):A22-7.
Jenni OG and O’Connor BB. 2005. Children’s sleep: An interplay between culture and biology. Pediatrics 115: 204-215.
Mindell JA, Kuhn B, Lewin DS, Meltzer LJ, Sadeh A and the
American Academy of Sleep Medicine. 2006. Behavioral treatment of
bedtime problems and night wakings in infants and young children. Sleep
Worthman CM and Melby M. 2002. Toward a comparative
developmental ecology of human sleep. In: Adolescent Sleep Patterns:
Biological, Social, and Psychological Influences, M.A. Carskadon, ed.
New York: Cambridge University Press, pp. 69-117.
Wright KP Jr1, McHill AW, Birks BR, Griffin BR, Rusterholz T, and Chinoy ED. 2013. Entrainment of the human circadian clock to the natural light-dark cycle. Curr Biol. 23(16):1554-8.
G, Kaplan H, Gurven M, Wood B, Ponzer H, Manger PR, Wilson C, McGregor
R, and Siegel J. 2015.Natural sleep and its seasonal variations in three
preindustrial societies. Current Biology. Epub ahead of print DOI:
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