BLOG: Sleep, School & Children
20th May 13
Tim Olds & Lisa Matricciani, Health and Use of Time (HUT) Group, University of South Australia
I believe the greatest asset a head of state can have is the ability to get a good night's sleep.
The Australian government has issued guidelines about physical activity, screen time and a wide range of dietary habits, but there are no guidelines around sleep. Yet a growing body of evidence tells us that good sleep is critical for physical and psychological health, academic performance, and learning motor skills. There is also strong evidence that kids are not getting enough sleep. Sleep is something every educator should be interested in. In this blog, we will provide a brief description of current trends in sleep studies relevant to educators. We will describe how much kids in Australia and overseas actually sleep; historical trends in sleep; how poor sleep impacts on kids; the importance of bedtime; and we will finish with a possible solution to address lack of sleep.
There was never a child so lovely but his mother was glad to get him to sleep.
Ralph Waldo Emerson
Children’s sleep is affected by sex, age, day type (school day or weekend), and the country where the child lives. These factors also interact in complex ways. Sleep duration declines about 10 minutes per year from age 9 until age 18. So while 9 year olds sleep about 10 hours a night, averaged over the week, 18 year olds will sleep about 8.5 hours. Kids sleep less on school days than on weekends, and the difference increases with age (Olds, Maher, Blunden & Matricciani, 2010). Ten year olds spend about the same amount of time sleeping on school days and weekends, but in 18 year olds, the difference is about 2 hours. Older adolescents have a pattern of “yo-yo” sleeping, with short school day sleeps alternating with long catch-up sleeps on the weekend.
Girls sleep a little more than boys, mainly because they get to bed earlier on weekends. Kids from wealthy households sleep a little longer, mainly on Sunday nights, probably because of parental control over bedtimes. Obese kids sleep less than lean kids, the difference being extremely marked on Sundays (a gap of almost one hour) (Olds, Blunden, Forchino & Petkov, 2010). There are also yearly cycles. Kids (like adults) sleep about 12 minutes more in winter than in summer, mainly because it is a little harder to drag them out of bed on cold mornings.
There are very big differences among adolescents from different countries. Around the world, Australians and Europeans sleep the most. Americans sleep about one hour less each night, and Asians about two hours less.
Trends in sleep
Once you wake up and smell the coffee, it's hard to go back to sleep.
There is a common belief that children are sleeping less now than they have in the past, but until recently, the evidence around this question was very weak (Matricciani, Olds & Williams, 2011). However, a recent meta-analysis of almost 700,000 children from 20 countries, going back over 100 years (Matricciani, Olds & Petkov, 2012) found that, on average, children have been losing sleep at the rate of about 45 seconds each year for over a century (Figure 1). In other words, children today sleep about 20-25 minutes less each day than their parents did when they were their age, and in turn their parents slept 20-25 minutes less than their grandparents. Declines have been greater on school days than on weekend days, exacerbating the pattern of “yo-yo” sleeping we see so often in older adolescents today. Declines have also been greater in older adolescents.
Figure 1. Changes in sleep over the last century in children of different ages. The line in the middle of the boxes represents the average change (in minutes of sleep per year).
IQR = interquartile range
Over the 100 year period, Australia has gone against the trend, and sleep durations have increased. However, there have been falls in recent years. Jim Dollman and his colleagues (Dollman, Ridley, Olds & Lowe, 2007) revisited in 2004 the same schools in South Australia that had been part of the 1985 National Health and Fitness Survey, and asked children of the same age the same questions about their sleep habits. They found that over that 19-year period, average sleep duration had fallen by about 30 minutes, mainly due to later bedtimes.
Why has this happened? Two factors seem to be important here: electricity has given us a reason to stay awake, and caffeine has made it possible.
Consequences of poor sleep
Sleep is the interest we have to pay on the capital which is called in at death; and the higher the rate of interest and the more regularly it is paid, the further the date of redemption is postponed.
There is an abundant literature on the consequences of poor sleep for cognitive and social functioning. Chronic low quality and low duration sleep have been associated with a range of psychosocial and physical disturbances in both adults and children, including impaired attention, memory consolidation, creativity, learning and academic performance (Dahl, 1996); motor skill deficits (Kuriyama, Stickgold & Walker, 2004); greater emotional liability, increased impulsivity, aggression and hyperactivity (Blunden, Hoban & Chervin, 2006); increased potential for alcohol and drug abuse in adulthood (Wong, Brower, Fitzgerald & Zucker, 2004); and suicide risk.
Short sleep duration is also associated with increased risk of overweight and obesity in children (Cappuccio et al, 2008; Olds, Blunden, Dollman & Maher, 2010) in both cross-sectional and longitudinal studies. This may be a result of hormonal changes associated with short sleep, including increased secretion of the hormone ghrelin, which stimulates appetite.
Sleep is necessary for memory consolidation, and this includes the procedural memory required for mastering skills, among them sports skills. Studies have consistently shown that when students do not have a good night’s sleep after learning a skill, there is no improvement the following day. After a good night’s sleep, skill performance improves dramatically. Dreaming (rapid eye movement or REM sleep) may be specially important for procedural memory.
What matters: Sleep or bedtime?
I have a constitutional weakness in which I am very easily distracted by flashing lights. If there is a TV on in the room, I can't have a conversation with you. I won't eat, I won't sleep, I'll just meld with my couch.
Most studies find that short sleep duration is associated with a greater risk of obesity, higher screen time, lower physical activity and poorer diet. But short sleep is mainly due to late bedtimes, and it is not easy to disentangle the effects of bedtime and sleep. Kids who go to bed late are more likely to be exposed to fast food, video games, and snacking while watching television. Kids who get up early are more likely to have breakfast, which is nutritionally sound, and have more opportunity to be physically active (for example, morning training or walking to school).
To try to unscramble the sleep-bedtime egg, we looked at data from the 2007 National Children’s Nutrition and Physical Activity Survey (Olds, Maher & Matricciani, 2011). We classified 9-16 year old kids into one of four categories, depending on the time they woke up, and the time they went to bed (adjusted for age and sex): Early to Bed, Early to Rise (EE); Early to Bed, Late to Rise (EL); Late to Bed, Early to Rise (LE); and Late to Bed, Late to Rise (LL). The EE and LL groups slept about the same amount (close to 9.5 hours), but the LL kids took fewer steps, were less physically active, watched much more television, played more videogames, ate more snack food and fast food, and less fruit and vegetables. Even when sleep duration was taken into account, kids with late bedtimes did much worse on almost every measure (Figure 2).
Figure 2. Risks of high screen time, low moderate to vigorous physical activity (MVPA), obesity and a combination of high screen time and low MVPA associated with different sleeping patterns, adjusted for sleep duration. The Late to Bed/Late to Rise (LL) pattern is consistently associated with greater risk.
School start time: A solution?
There is only one thing people like that is good for them: a good night's sleep.
Edgar Watson Howe
There is a debate in the US at the moment about adjusting high school start times to facilitate better sleep habits. Schools in the US typically start much earlier than in Australia (usually between 7:30 am and 8:00 am). As a result, adolescents need to get up very early to get to school (usually between 6:00 am and 6:30 am). In post-pubertal adolescents, physiological changes associated with time shifts in the secretion of the sleep-inducing hormone melatonin mean that kids get sleepy later. The combination of hormonally driven later bedtimes and socially driven early rise times means that sleep is curtailed.
One obvious solution would be to start school later. This suggestion has met with much resistance, largely from bus companies whose schedules would be disrupted, but also from groups such as sports coaches. There have been several studies looking into the benefits of later school start times. Some have failed to show benefits, but most report improvements in academic performance, absenteeism, attention and health (Carrell, Maghakian & West, 2010). Whether these benefits are translatable into the Australian context, where adolescents sleep more and school starts later, is a matter for debate.
In terms of academic performance, motor skills and general mental and physical health, sleep has for a long time been the “black hole” of children’s time use. It has now entered the mainstream of public debate. Over the last 100 years, various recommendations have been put forward with very little evidence (Mattricciani, Olds, Blunden, Rigney & Williams, 2012). There is now a great opportunity for schools and educators, researchers and parents to implement innovative trials to improve children’s sleep habits.
Blunden, S., Hoban, T.F., & Chervin, R.D. (2006). Sleepiness in children. Sleep Medicine Clinics, 1(1), 105-18.
Cappuccio, F.P., Taggart, F.M., Kandala, N.B., Currie, A., Peile, E., Stranges, S. et al. (2008). Meta-analysis of short sleep duration and obesity in children and adults. Sleep, 31(5), 593-4.
Carrell, S., Maghakian, T., & West, J.E. (2010). A's from zzzz's? The causal effect of school start time on the academic achievement of adolescents. American Economic Journal: Economic Policy, 3(3), 62–81.
Dahl, R.E. (1996). The impact of inadequate sleep on children's daytime cognitive function. Seminars in Pediatric Neurology, 3(1), 44-50.
Dollman, J., Ridley, K., Olds, T., & Lowe, L. (2007). Trends in the duration of school-day sleep among 10-15 year old South Australians 1985-2004. Acta Paediatrica, 96(7), 1011-1014.
Kuriyama, K., Stickgold, R., & Walker, M.P. (2004). Sleep-dependent learning and motor-skill complexity. Learning & Memory, 11(6), 705-13.
Matricciani, L.A., Olds, T., Blunden, S., Rigney, G., & Williams, M.T. (2012). Never enough sleep: a brief history of sleep recommendations for children. Pediatrics, 129(3), 458-556.
Matricciani, L., Olds, T., & Petkov, J. (2012). In search of lost sleep: Secular trends in the sleep time of school-aged children and adolescents. Sleep Medicine Reviews, 16(3), 203-211.
Matricciani, L., Olds, T., & Williams, M. (2011). A review of evidence for the claim that children are sleeping less than in the past. Sleep, 34(5), 651-659.
Olds, T.S., Blunden, S., Dollman, J. & Maher, C. (2010). Day type and the relationship between weight status and sleep duration in children and adolescents. Australian and NZ Journal of Public Health, 34(2),165-171.
Olds, T.S., Blunden, S., Forchino, & Petkov, J. (2010). The relationships between sex, age, geography and time in bed in adolescents: a meta-analysis of data from 23 countries. Sleep Medicine Reviews, 14(6), 371-378.
Olds , T., Maher, C., Blunden, S., & Matricciani, L. (2010). Normative data on the sleep habits of Australian children and adolescents. Sleep, 33(10), 1381-1388.
Olds, T., Maher, C., & Matricciani, L. (2011). Sleep duration or bedtime? Exploring the relationship between sleep habits and weight status and activity patterns. Sleep, 34(10), 1299-1307.
Wong, M.M., Brower, K.J., Fitzgerald H.E., & Zucker, R.A. (2004). Sleep problems in early childhood and early onset of alcohol and other drug use in adolescence. Alcohol: Clinical & Experimental Research, 28(4), 578-87.
This article first appeared in ACHPER's Active & Healthy Magazine Volume 19 Issue 2 2012. To subscribe, click here.