The Pfizer Australia Health Report looks at sleep, why we need it, what can go wrong and how we can improve it.

There are nearly 70 clinically diagnosable sleep disorders. Some of the most frequent sleep disorders are:

Insomnia (an inability to either fall asleep or maintain sleep)

• Snoring
• Sleep Apnoea Syndromes
• Sleep Deprivation or lack of sleep
• A sleep disorder as a result of shiftwork
• Narcolepsy
• Restless legs and Periodic Limb Movement Disorder
• Parasomnias (sleep behavioural disorders or “things that go bump in the night”) for example: sleep terrors, nightmares and sleep walking and talking
• Circadian Rhythm (biological clock) Disorders (largely through jet-lag and shift work).

In the 2004 report “Wake Up Australia”, analysts Access Economics estimated costs incurred through lost productivity, cost of treatment, morbidity and death.
“We estimate that over 1.2 million Australians (6 percent of the population) experience sleep disorders,”.

Some illnesses such as heartburn, asthma, depression and heart disease can impact sleep quality and can be worse during sleep periods. Certain medications and alcohol can affect sleep, sleep patterns and quality of sleep.

We do know that sleep is required for laying down memory, to save the body’s energy, to restore daytime mental function and for physical growth. Sleep, however, is an active process and studies have shown increased activity of certain parts of our brain when we sleep when compared to wakefulness. Yet, during sleep our blood pressure, heart rate, breathing and body temperature decrease compared to wakefulness.

Lack of good sleep due to a sleep disorder or sleep deprivation can lead to a number of daytime consequences including excessive daytime sleepiness, tiredness and lethargy, morning headache, or neurocognitive dysfunction such as poor memory, anxiety and depression.

The type and duration of sleep we have changes during our lifetime. For example, a newborn child will sleep almost all day apart from when feeding or uncomfortable, and the type of sleep is quite different to adolescents and adults. As we get older we have less deep sleep (Slow Wave Sleep) and less Rapid Eye Movement sleep (the type of sleep when we usually dream). In addition, of the one in ten who use sleeping tablets, a third admit to taking them every night.

Associate Professor Harry Teichtahl from the Australasian Sleep Association is concerned at the high use of sleep medications in the community because he believes they often don’t address the cause of the sleeping problem. And according to the findings, sleep disturbances aren’t just a problem for those taking sleeping tablets.

Twenty percent reported being disturbed between three and five times every night. Close to two-thirds reported difficulty going to sleep. Two-in-five say they do not wake up feeling refreshed and close to two-thirds feel sleepy during the day more often than once a week. Not surprisingly, more than 70 percent of those surveyed feel their ability to get to sleep is affected by the level of work/school or everyday stresses, and that they sleep better when relaxed.

Other key findings in this Pfizer Australia Health Report show that:

• Just under 25 percent of Australians have their sleep disrupted by others in the household who snore on a regular basis
• On average, Australians feel sleepy for approximately five months of the year
• Just over 25 percent of Australians have their sleep regularly interrupted because others in the household have different hours of sleep.

Is sleep essential? Ask that question to a sleep-deprived new parent or a student who has just pulled an "all-nighter," and the answer will be a grouchy, "Of course!"

But to a sleep scientist, the question of what constitutes sleep is so complex that scientists are still trying to define the essential function of something we do every night. The search for the core function of sleep can seem as elusive as the search for the mythological phoenix, says Cirelli, an associate professor of psychiatry at the University of Wisconsin School of Medicine and Public Health in Madison.

Some scientists argue that sleep is merely a way to impose a quiet, immobile state (rest), and isn't important by itself in mammals and birds. This is the rejected so-called "null hypothesis,".

"We don't understand the purpose of sleep, but it must be important because all animals do it," There's no clear evidence of an animal species that doesn't sleep, she says. Even the dolphin—which is sometimes held up as an animal that doesn't sleep because it moves continuously—will show "uni-hemispheric sleep" with one eye closed and one half its brain showing the slow waves characteristic of deep sleep.

"The very fact that dolphins have developed the remarkable specialisation, rather than merely getting rid of sleep altogether, should count as evidence that sleep must serve some essential function and cannot be eliminated,"

She also argues that sleep is strictly regulated by the brain, because sleep deprivation is followed by a rebound, in which the sleep-deprived animal either sleeps longer, or spends more time in the deeper sleep characterised by large slow brain waves. Prolonged sleep deprivation has been shown to kill rats, flies and cockroaches. Humans who have a genetic insomnia can also die. In less extreme cases, sleep deprivation affects cognitive function in animals ranging from flies to rodents. Rats kept awake will engage in "micro-sleep" episodes, and sleep-deprived humans tend to fall asleep even in the most dangerous circumstances. Because it is universal, tightly regulated, and cannot be lost without serious harm, that sleep must have an important core function. But what? "Sleep may be the price you pay so your brain can be plastic the next day," Cirelli says.

Their hypothesis is that sleep allows the brain to regroup after a hard day of learning by giving the synapses, which increase in strength during the day, a chance to damp down to baseline levels. This is important because the brain uses up to 80 percent of its energy to sustain synaptic activity.

Sleep may also be important for consolidating new memories, and to allow the brain to "forget" the random, unimportant impressions of the day, so there is room for more learning the next day. This could be why the brain waves are so active during certain periods of sleep."While there may still be no consensus on why animals need to sleep, it would seem that searching for a core function of sleep, particularly at the cellular level, is still a worthwhile exercise," she concludes.
Journal reference:

1. Cirelli C, Tononi G. Is sleep essential? PLoS Biol, 2008; 6(8): e216 DOI: 10.1371/journal.pbio.0060216