Study of sleep through the ages shines light on modern-day disruption to rest patterns, as John Illman discovers
Most of us think of a good night’s rest as seven to eight hours of undisturbed slumber, but in the pre-light bulb era we would sleep for three or four hours, wake up for two or three hours and then sleep again until morning.
The precious leisure time in between sleeps was spent with the family, visiting neighbours, reading, writing, reciting prayers specifically written for midnight, and contemplating. Scientists are now speculating that this time, in which people were forced into periods of rest and relaxation, may have played a critical part in helping the body to handle stress.
Midnight leisure hours were also spent making love. This advice from a 16th-century French medical manual may resonate with millions of today’s lovers. It advises couples that the best time to conceive is not after a hard day’s work, but “after the first sleep” when “they have more enjoyment” and “do it better”.
So when and why did things change? Roger Ekirch, professor of history at Virginia Tech, is perhaps the world’s foremost authority on segmented sleeping. His book, At Day’s Close: Night in Times Past, includes more than 500 references from medical books, diaries, court records and literature, from Homer’s Odyssey to modern Nigerian tribes.
References to segmented sleeping in Europe, he found, began to disappear in the late-17th century. Increasingly, with improvements in street lighting and the rise of coffee houses that sometimes remained opening until late in the evening, night became a time to socialise. Lying in bed was considered a waste of time.
Even sleep itself was condemned. Following the first public demonstration of his incandescent light bulb in 1878, Thomas Edison declared that sleep was “a criminal waste of time and a heritage of our caveman days”.
His discovery was the catalyst for today’s 24/7 society, and a head-on collision between natural evolution and scientific revolution. Although most of us seem to adapt well to modern sleep cycles, many scientists believe that many sleeping problems may be linked to ubiquitous artificial light and the body’s natural preference for segmented sleep.
Light regulates our sleep patterns; it is one of life’s driving forces, the key to the rhythm of life. Over millions of years we have incorporated the rhythms of light and darkness, night and day, into our bodies thanks to the master biological clock and a pea-sized gland in the centre of the brain.
The pineal gland has intrigued scientists ever since it as acclaimed as the seat of the soul by the 17th-century philosopher René Descartes. It is also known as “the third eye” because it keeps the body informed about any changes in day length. The pineal produces the sleep hormone melatonin. Darkness is a signal for it to make melatonin and light a signal for it to stop doing so.
Scientists dismissed the idea that our biological rhythms were light-dependent until some pivotal research beginning about 25 years ago. Artificial light, scientists had believed, made us immune to the same light-dark adaptations experienced by our ancestors and the rest of the animal kingdom. They couldn’t have been more wrong.
Our ancestors from cave-dwelling times enjoyed sleep in total darkness and woke when light hit sensors on the eyes to signal the time to hunt
Inspired by a movie about primitive humans, who lived before the onset of artificial lighting, Thomas Wehr, a psychiatrist at the US National Institute of Mental Health, wondered about their lives and how they had slept and felt during their waking hours.
In one of his studies, a group was plunged into darkness for 14 hours every day for a month. It took some time for their sleep to regulate, but by the fourth week they had adopted a new sleeping pattern. They slept first for four hours and woke up for one or two hours before falling into a second four-hour sleep; in other words they assumed the characteristic segmented sleep of our forebears.
During their exposure to extended darkness, the subjects were also prone to increased levels of prolactin, a hormone that increases during meditative states. This could explain why they were not anxious while awake in the dark, unlike insomniacs who often are. In contrast, they experienced a peaceful stillness. Prolactin secretion is believed to account for the serene nature of polar animals as they rest in the frozen wilderness waiting for the return of light.
One further observation from Dr Wehr’s study was both remarkable and disturbing. The group reported a “crystal-clear consciousness” when awake. In his book, Winter Blues, pioneer researcher Professor Norman Rosenthal commented: “This finding suggests that many modern people may walk around in a less wide-awake state as a result of chronic sleep deprivation.”
In Britain, Russell Foster, professor of circadian neuroscience and head of the department of ophthalmology at the University of Oxford, has warned that we are “desperately sleep deprived”. In the 1950s, he says, most people were getting about eight hours of sleep a night; now it is one-and-a-half to two hours less.
In a recent TED (technology, entertainment, design) lecture, Professor Foster warns: “For teenagers it’s worse – much worse. They need nine hours sleep a night for full brain performance. Many of them are only getting five.”
Night-time light exposure can exacerbate sleeplessness by throwing the biological clock out of synch, winding the brain up instead of down. Blue wavelengths, which are beneficial during daylight hours because they boost attention, reaction times and mood, seem to be most disruptive at night. Our ancestors from cave-dwelling times enjoyed sleep in total darkness and woke when light hit sensors on the eyes to signal the time to hunt. It was a survival cycle that is still in us.
But the proliferation of TVs, computers and energy-efficient lighting is increasing exposure to blue wavelengths that we associate with daytime function. Dr Stephen Lockley, of Harvard Medical School, says that even a dim light can interfere with the body clock and melatonin secretions. There is some very preliminary experimental evidence linking low melatonin levels to cancer.
It is not clear why night-time light exposure seems to be so bad for us, but tired people are vulnerable to sustained stress and this may suppress immunity. Scientists like Professor Foster believe that in turn this may be associated with increased risk of cardiovascular disease and diabetes as well as cancer.
He is especially concerned about the widespread use of caffeine and alcohol to fight fatigue. “If you are tired, your brain will crave things to wake it up. Much of the day may be fuelled by caffeine. Then you get to 11 at night and the brain says: ‘I need to be asleep shortly. What are we doing about that when I feel completely wired?’ You then resort to alcohol. But alcohol doesn’t provide sleep. It sedates you. It actually harms some of the neural processing that is going on,” says Professor Foster.
Dave Gibson vividly identifies with this picture. He has made a special study of sleep after his own experience of sleeplessness during 15 years in advertising. He now works as an osteopath and sleep adviser for Warren Evans, one of the UK’s biggest manufacturers of beds and mattresses.
He recalls: “In advertising, I was repeatedly working late at night and, during the last two or three years, I was using alcohol to get to sleep – to knock myself out. I became depressed.”
Today, he says, he can see his old self in many of his City patients and tries to encourage them to do what he did – focus on things they can change, such as diet, exercise and sleep.
The dangers of alcohol are well known, but is sleep deprivation really such a big problem? We are, after all, living longer than ever before. In contrast, life expectancy in the 16th century, when segmented sleeping was fashionable, is believed to have been about 35.
But Debra Skene, professor of neuroendocrinology at the University of Surrey and a leading sleep researcher, says: “This is true, but I wonder for how much longer. I wake up every morning to reports of increased obesity, diabetes and cardiovascular disease.”