Society has changed enormously over the past century, not least in the way we sleep. Light bulbs, television, computers and shift work have all altered traditional sleeping habits. This has huge implications not only for sleep deprivation, but also for our health. New discoveries about sleep and sleeplessness may help us cope with future change
Sleepless society?
It is often said that we sleep less than we used to. Half a century ago people supposedly slept for more than 8 hours a night while we now sleep for 7 on average.
The evidence for this is not particularly convincing, simply because 50 years ago scientists weren鈥檛 too interested in how much people were sleeping. However, there is no doubt that some of us are sleep-deprived. Fortunately we also understand the effects of sleeplessness better than ever.
Advertisement
Sleeplessness is bad for you. A fifth of road accidents are linked to fatigue. Sleep deprivation also affects health directly: the past decade has seen several epidemiological studies linking sleeplessness to ill health and higher mortality rates. For example, there is a link between a decrease in sleep and a rise in obesity and diabetes, which might be explained by the way sleep deprivation disrupts appetite mechanisms and stimulates hunger ().
A 17-year study of more than 10,000 British civil servants found that those who had cut their sleep from 7 to fewer than 5 hours were 1.78 times more likely to die from all causes. For example, risk of death from cardiovascular disease rose by 2.25 times ().
It is not just sleep deprivation that is unhealthy. Sleeping too long is also associated with an increased risk of dying compared with people who sleep for the optimum period, though reasons are unknown (see diagram).
A better understanding of insomnia is also urgently needed, since it damages the performance of businesses to the tune of around $60 billion per year in the US alone ().
There are more subtle effects of sleeplessness. One study suggests that sleep deprivation increases the activity of the amygdala, a region of the brain involved in the regulation of anxiety and mood. In addition, some form of sleep disruption is found in almost all psychiatric disorders ().
New ways to snooze
Sleeping pills (or hypnotics) are designed to mimic the mechanisms of natural sleep, which involve many molecules that transmit information in the brain and body, such as neurotransmitters and hormones. Most hypnotics target specific neurotransmitters and the receptor sites in the brain on which they act, especially GABA, the brain鈥檚 principal inhibitory signalling molecule. Some hypnotics target hormones such as melatonin.
Most of these drugs are effective, the newer ones especially so. But they all alter sleep structure and brainwaves to some extent and most sleep medications have side effects such as grogginess the next morning or memory loss for events that happened while awake during the night.
Based on new understanding of the circuits involved in the sleep-wake cycle, there are drugs in development for the treatment of insomnia. They target several proteins in the brain on which messenger chemicals act, such as the receptors for serotonin, orexin, histamine or melatonin. Some of these new drugs appear to change only the timing or duration of sleep, without changes in the generation of brainwaves. If these findings are supported by bigger studies, these drugs promise to be valuable advances on current sleeping pills.
New ways to rise
In the modern world many of us need an alarm clock to rouse us. Left to our own devices, however, we eventually wake up. The signal to do so is generated in a region of the brain called the suprachiasmatic nucleus (SCN) in the hypothalamus. This plays a central role in sleep-wake timing by regulating the rhythms of hormones such as melatonin, as well as neurotransmitters and neuromodulators such as orexins.
Because the internal wake-up call is gentle, it is easy to oversleep. Furthermore, the call often arrives a bit late because most of us have a body clock that naturally runs for longer than 24 hours. Exposure to light from cellphones, TVs and computers in the evening may also shift the clock to a later hour, making matters worse.
In the absence of an alarm clock, we most often wake up during REM sleep, which some sleep scientists have called the 鈥済ate to wakefulness鈥�. Large parts of the brain are active during REM sleep and switching to fully alert wakefulness may therefore be easier. But during deep sleep many brain areas are deactivated. If woken from this state by an alarm clock (or at the end of a long afternoon nap) we feel groggy.
There are new kinds of alarm clock that attempt to ensure a more pleasant awakening. offers a way to monitor sleep states to ensure the alarm happens during REM sleep, and cellphones and wrist-based monitors claim to detect differences of movement between REM sleep and non-REM sleep, again with the aim of ensuring a more gentle crossing into consciousness. Another approach is to use light: after all, the light-dark cycle is the natural timekeeper and light remains the alarm clock par excellence.
鈥淭he light-dark cycle is the natural timekeeper and light remains the alarm clock par excellence鈥�