Some people argue that they are "night people"who function best after midnight. However, I believethis is highly unlikely. Rather, they have lost alltouch with their natural cycles. Evolution tells usthat if there were night people, they would probablyhave been eaten by a wild beast or fallen down a deepravine somewhere. Our night vision is pathetic; it isonly since the electric light that some people havebegun to consider themselves as night people. Kids startout as morning people, but tend to adopt late-nighthabits as they age and follow the patterns of the parents.One friend recently told me that the late nights atuniversity changed him into a night person, but hisyoung children have now changed him back.
Our ancestors of some 50,000 years ago slept betweeneight and 10 hours each night and rose just before sunlight.The hunter-gatherer's sleeping and waking cycle wasbased on nothing but internal and psychological cueslinked with the natural sunlight. Even in recent history,we slept more than we do now. In 1910, the average sleeptime was nine hours compared to seven hours or fewerin 2005 - thanks to Thomas Edison, work and the television.
Every night, just before we fall asleep, we experiencehypnagogic imagery -- a state described as dreaming,drowsy, floating, wandering a few minutes in a stateof relaxed wakefulness characterised by drifting thoughtsand alpha brainwaves. Awareness of this state has beenreported as essential to creativity and genius. AlbertEinstein, Mark Twain, Edgar Allen Poe and Robert LouisStephenson all incorporated spontaneous imagery in theircreative endeavours. August Kekule discovered the benzenering in chemistry from a hypnagogic image (during adream-like state) of a snake biting its own tail. Thisdiscovery led to the chemistry to build many elementsof the modern world from plastics to pharmaceuticals.
The times at which a person falls asleep and wakesup is largely determined by his circadian rhythm, aday-night cycle of about 24 hours. The normal rhythmis reset daily by the influence of bright light in themorning. Shift workers who work at night and sleep inthe daytime and people who are blind may have difficultymaintaining a normal sleep-wake cycle because they arenot able to see natural environmental cues.
Among the theories about why humans sleep, scientistshave proposed that sleep may be a way of rechargingthe brain. It gives the brain an opportunity to reorganisedata to help find solutions to problems, process newlylearned information and organise and archive memories.The cardiovascular system also gets a break during sleep.People with normal or high blood pressure experiencea 20 to 30 per cent reduction in blood pressure andup to 20 per cent reduction in heart rate. During sleep,the body has a chance to replace chemicals and repairmuscles, other tissues and ageing or dead cells; andin children and young adults, growth hormones are releasedduring deep sleep.
All of the theories above underscore that sleep isessential as well as bestowing other benefits including:Feeling restedBeing physically and mentally alertHaving more energyMaking fewer mistakes (including causing accidents)Feeling psychologically and emotionally recovered.
Sleep allows us to experience:Improved cognitive functionImproved memoryHigher stress tolerance and resilienceIncreased productivityNormal body balanceHealthier weightReduced risk of CVD, diabetes and cancerLiving longer andFeeling healthier
Getting enough sleep is associated with energy, joy,optimistic thinking and coping with negative emotions.Despite this, almost 90 per cent of Australians sufferfrom some type sleep disorder at some stage of theirlives. Of these, 30 per cent suffer from severe sleepdisorders. Very few people regularly enjoy the amountor quality of sleep that they need. The estimated economiccosts to the country from this are between $3 billionand $7 billion annually, not to mention the huge, unmeasuredphysical, psychological, emotional and social costs.Similarly, research on sleep deprivation suggests thatthe result of missing an entire night of sleep is equalto an IQ drop of 10 points. This IQ drop was even moresignificant in men who took part in the tests than inwomen. Symptoms of sleep deprivation include constantyawning, the tendency to doze off when not active fora while (for example, when watching television), grogginesswhen waking in the morning, sleepy grogginess experiencedall day long (sleep inertia), a lack of ability to concentrate,and moodiness. After approximately 20 hours of no sleep,reaction times are comparable to having a blood alcoholreading of 0.08. Staying awake for 24 hours leads toa reduced hand-to-eye coordination that is similar tohaving a blood alcohol content of 0.10!
Numerous studies have shown that even a little bitof sleep deprivation decreases efficiency and increasesthe risk of disease, including cardiovascular disease.Sleep deprivation has been shown to negatively affectendocrine (hormones) and metabolic functioning, as wellas nervous system balance. Sleep deprivation is associatedwith an increased concentration of cortisol, plus otherindicators of increased stress such as elevations inpulse rate, body temperature and adrenaline secretion.Sleep deprivation also appears to increase blood concentrationsof certain chemicals called cytokines and C-reactiveproteins, indicating an inflammatory reaction. The effectof unremitting low-grade inflammation may be to damagethe inner walls of the arteries, which sometimes leadsto vessel narrowing, high blood pressure, stroke, andheart disease. During truncated sleep, your heart mighthave to work harder, constricting blood vessels andincreasing blood pressure even more, which could conceivablyresult in a heart attack or stroke.
A study of 71,617 female health professionals foundthat sleeping fewer than five hours per night was associatedwith a 39 per cent increase in the risk of coronaryheart disease; even six hours per night showed an increaseof 18 per cent compared to sleeping eight hours pernight. In an analysis of data on more than one millionpeople, the levels of nearly all forms of death weretwo-and-a-half times higher for people who slept fourhours or fewer compared to those who slept between sevenand eight hours on average.
Several recent studies report that reducing sleep to6.5 or fewer hours for successive nights causes potentiallyharmful metabolic, hormonal and immune changes. Allof the changes are similar to those detected in thenormal ageing process, and so sleep deprivation couldbe the biggest indicator of how long you live. Thereis a strong link between sleep deprivation and low immunesystem function. A reduction of sleep makes people moreprone to infection and potentially more prone to cancer;one study found that poor sleep was associated witha 60 per cent increase in breast cancer.
Experimentally, sleep deprivation has been shown tonegatively affect glucose metabolism and to enhancefactors associated with Type 2 diabetes and people whoexperience sleep disorders were as much as three timesas likely to develop Type 2 diabetes. Subjects in onestudy demonstrated impaired glucose tolerance for 10days after four hours of sleep deprivation. It is alsosuggested that sleep deprivation may play a role inobesity levels. Sleep deficits bring about physiologicchanges in the hormonal signals that promote hungerand, perhaps thereby, obesity. One study found thatafter two days of sleep curtailment, the subjects hadreduced levels of the fat-derived hormone leptin andincreased levels of the stomach-derived hormone ghrelin.These hormones are responsible for regulating hungerand appetite. These hormonal differences are likelyto increase appetite, which could help explain the relativehigh Body Mass index (BMI) in short sleepers.
Lack of sleep also has detrimental effects specificto children. Sleepy children tend to speed up ratherthan slow down. As a result, some people believe thata child has Attention Deficit Hyperactivity Disorder(ADHD) rather than the simpler explanation of the childsimply not getting enough sleep. A recent study foundsleep disorders were strongly associated with ADHD andthat the sleep disorders had appeared well before theADHD symptoms. Symptoms of sleep disorders in childreninclude:Moodiness and irritabilityTemper tantrumsThe tendency to emotionally "explode"at the slightest provocationOver-activity and hyperactive behaviourDaytime napsGrogginess upon waking in the morningReluctance to get out of bed in the morningReduced school performanceIncreased risk of emotional problems such as depressionIncreased naughtinessPoor concentrationIncreased problems with impulse control and subsequentincrease in risk-taking behaviours.
Other research has linked academic and behaviouralproblems in adolescents to irregular sleep patterns.Early school start times for adolescents are frequentlyassociated with significant sleep deprivation, whichcan lead to academic, behavioural and psychologicalproblems. High school students who regularly score C,D or F on school tests and assignments get, on average,half an hour less sleep per night than high school studentswho regularly get A and B grades.
So perhaps it's time to turn off the telly, the computer,the iPod and the myriad other electronic distractionsthat keep us up and about long after we should be inbed. And, instead of pushing our kids to that extrahour of late-night study, extol the virtues of a brightand alert start to the day after a good night's sleep.
Peter Dingle is Associate Professor inHealth and the Environment
at Murdoch University, Perth, Western Australia