Time to set our clocks right

The 19th century French emperor Napoleon Bonaparte had a theory about sleep. “Six hours for a man, seven for a woman and eight for a fool,” he believed.

Napoleon shared a societal belief that persists to this day; that people who sleep in late or for a long time are lazy.

However, science is discovering that sleep patterns and the effects they have on us are not as simple as that. The biological truth is that we are all controlled by our own complex internal clocks, which not only dictate when we sleep and for how long, but also trigger a range of other vital functions.

The amount of sleep a person requires is as individual as a fingerprint. Some of us manage on very little; former British Prime Minister the late Margaret Thatcher famously survived on four hours of sleep a night. Others need a bit more shut-eye to function properly. Scientist Albert Einstein needed ten hours.

Every living organism has some form of biological clock, which is synchronised by a range of different stimuli. In animals biological clocks control cyclical patterns such as eating, sleeping, mating, hibernating, migration and cellular regeneration. In plants they control leaf movements and photosynthesis, and they have even been found at work in microscopic organisms such as bacteria.

The science of biological clocks is called chronobiology, and chronobiologists study cyclical behaviours in living organisms, which follow patterns controlled by these clocks. The most important of these patterns are circadian rhythms; these are physical, mental and behavioural changes that follow a daily cycle (the name derives from the Latin for ‘about’ – circa – and the Latin for ‘day’ – diem).

Circadian rhythms are driven by the changes in light and darkness in an organism’s environment, and because of this they follow a 24-hour pattern.

Don’t disrupt the cycle

The most obvious circadian rhythm in humans is our sleep cycle. Each of us has an individual pattern of sleep called our chronotype. Disruption of this has physical consequences.

For example, when we fly into a different time zone we suffer jet lag, or desynchronosis to give it its medical term. The severity of the jet lag depends on the difference in the time zones a traveller departs from and arrives into and the time it takes to travel between the two.

In most cases jet leg presents itself as sleep disruption, but in severe cases symptoms include poorer performance on mental tasks and concentration, increased fatigue, headaches, irritability, problems with digestion and reduced appetite. It can take the body several days to reset its internal clock and adjust to the new time zone it finds itself in.

As well as sleep, circadian rhythms can also influence hormone release, body temperature and other important bodily functions. Abnormal circadian rhythms have been associated with obesity, diabetes, depression, bipolar disorder and seasonal affective disorder.

Many actions in organisms triggered by biological clocks occur along with changes in external factors such as light and temperature. A lot of the seasonal changes in animals and plants are influenced by changes in day length. For example, birds know to migrate when the days get shorter, and in plants germination and flowering will generally begin to occur when daylight increases.

But natural external changes aren’t the only factors that stimulate biological clocks – there are also internal mechanisms at play. This explains why, in botanical studies, a mimosa plant kept in a dark cupboard will open and close its leaves as if still experiencing natural changes in light, and why humans confined to dark bunkers follow the same sleeping patterns they had in normal night and day conditions.

It’s all in the genes

Chronobiologists have discovered that our biological clocks are governed not only by the sun, the moon, the seasons and the tides, but are also controlled by our genes.

On a genetic level, individual clock genes switch on and off to control behaviours and, most prominently, we have a master clock situated in our brain, which is believed to control these genes.

The master clock is in an area of the brain called the suprachiasmatic nucleus, or SCN, a small region of around 20,000 cells in the centre of the brain that regulates neural and hormonal activity. It controls the production of melatonin, a hormone that promotes sleep. Because it is located just above the optic nerve, which relays information from the eyes to the brain, the SCN receives information about incoming light. When there is less light the SCN tells the brain to make more melatonin.

Our biological clocks have ticked away effectively for millions of years, finely tuned to the natural environment. For people such as farmers and tribesmen, who spend much of their lives close to nature, there is little to disrupt these internal time mechanisms. However, modern urban lifestyles are increasingly being found to play havoc with natural body clocks.

The artificial way in which society structures days around home and work, which chronobiologists call ‘social time’, can have a serious effect on health.

German chronobiologist Till Roenneberg has researched the effects these changes in lifestyle have had on our biological clocks and he believes the disconnect between our internal biological time and the social time that defines our lives leads to an effect he calls social jet lag; a kind of chronic exhaustion resembling the symptoms of jet lag and comparable to having to work for a company a few time zones to the east of your home.
Unlike real jet lag, which is temporary, social jet lag is chronic because people suffering from it never manage to adjust to the environment that is altering their biological clock.

There are many reasons for the increase of social jet lag. One of the most prevalent is the rise in popularity of shift work. Nearly 20 per cent of wage earners in industrialised countries now work after dark, compared to preindustrial communities where few people worked shifts.

The outsourcing of call centres to distant countries is another cause. Employees live in one time zone but work in another to accommodate the waking hours of their customers. Meals, sleep and social occasions run counter to a worker’s biological clock, resulting in heightened stress and a greater likelihood of illness.
In his book, Internal Time: Chronotypes, Social Jet Lag, and Why You’re So Tired, Roenneberg explains that over 40 per cent of the Central European population suffers from social jet lag of two hours or more, and the biological clocks of over 15 per cent are three hours or more out of sync with external time. These levels are projected to be the same in other industrialised nations.

The level of social jet lag can be measured by the difference between a person’s sleep pattern on a work or school day and on a free day. The bigger the difference, the more social jet lag the subject experiences. This redistribution of sleeping patterns has serious consequences.

Shifting opinions

Roenneberg calls shift work, “one of the most blatant assaults on the body clock in modern society.” And experts at the World Health Organization agree. They recently classified shift work that involves circadian disruption as a potential cause of cancer.

Roenneberg writes, “Large portions of society suffer from too little sleep during the workweek. Sleep debt and long sleep inertia times are known to decrease attention, performance, mood and memory.”

He continues, “The consequences are multifarious, ranging from higher accident rates due to increased sleep inertia and decreased vigilance to learning deficits in adolescents due to disturbed sleep patterns.”
But it is not just workers who suffer from social jet lag. It is increasingly believed that the school day is out of sync with the natural body clock of the average adolescent. Some schools begin classes as early as 7am, which means pupils are required to rise and start work early.
 
But teenagers need around eight to ten hours of sleep a night, and research has found that they get much less during the week. A recent study found that when the starting time of high school is delayed by an hour, the students’ attendance rate, performance, motivation and even eating habits all improve significantly.
Roenneberg highlights a successful Danish project that eliminated timetables and let students decide when to arrive at school. The idea was based on a vision that schools should be regarded as service centres that tailor their service to what’s best for their customers.

We are only beginning to understand the potentially detrimental consequences of social jet lag. One of these has already been worked out with frightening certainty: the more severe the social jet lag, the more likely it is that people become smokers. And with a range of other health implications evident, it seems we ignore our biological clocks at our peril.