Sleep – the engine that powers our health

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"Sleep on it first" is sensible advice when an important decision needs to be taken. It is also well-founded advice from a sleep research perspective. After all, sleep is an extremely active physiological state even if we are not actually conscious at the time: our memories are consolidated when we sleep. Sleep helps us re-evaluate information and thus arrive at new insights.

But that is by no means all that sleep does: “We learn in our sleep, save energy, recharge our batteries, fight diseases, slow the ageing process, strengthen our immune system and clean the brain – and do so in a state in which we are active, just like when we are awake, but on a different level”, says Professor Ingo Fietze, head of the Interdisciplinary Center for Sleep Medicine at the Charité in Berlin.

When we stop breathing in our sleep

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It was only with the advent of electroencephalography (EEG) that brain researchers were able to prove that sleep is a state in which we are both physically and mentally active. The neurologist and psychiatrist Hans Berger came up with this invention in the 1920s at the University of Jena. In the 1930s, brain researchers first discovered a characteristic sleep pattern. Today, sleep researchers distinguish between four phases that include light sleep, deep sleep and a dream phase that, in terms of blood pressure and pulse, is equivalent to our waking state.

It was not until the 1980s that doctors began to focus on sleep. This was when sleep apnoea was discovered – a condition that sees people stop breathing for a time while asleep. This disrupts their night rest to such an extent that they fall asleep spontaneously and unintentionally during the day. Because this disorder has an organic cause, cardiologists, pulmonologists and neurologists joined brain researchers and psychologists in studying sleep. In Germany, the first sleep medicine centres for the treatment of sleep disorders were established. Nowadays there are more than 300 sleep labs that have been accredited by the German Sleep Society.

Sleep disorders and depression

According to sleep researchers, roughly 10 to 15 percent of people suffer from pathological sleep disorders. The causes range from stress, noise, shift work, alcohol consumption and dietary habits to physical causes such as cardiovascular diseases. Psychological disorders such as depression can also cause problems with sleep. Depression is one example of how external influences and physiology are interrelated: a person who has not slept well for several weeks or months may end up suffering from depression. And in turn, depression often goes hand in hand with sleep disorders.

Professor Alex Steiger and his team at the Max Planck Institute of Psychiatry in Munich explore why this is the case, and how this interplay manifests itself in the body. To do so, they not only measure brain activity in their test subjects and patients in the sleep lab, but also take regular blood samples that allow them to track changes in hormone status. They have found that people with depression have different sleep cycles, and that the release of growth and stress hormones is also changed. On the basis of sleep profiles, the researchers can now ascertain within a week whether patients will respond to a particular antidepressant or not. In the past, this would take four or five weeks. Sleep clearly provides researchers with good advice, too.

Max Planck Institute of Psychiatry

The hospital of the Max Planck Institute of Psychiatry in Munich specialises particularly in diseases caused by stress. The Sleep Endocrinology research group uses measurements of brain activity to study the four sleep phases in humans. In their work, the scientists focus particularly on the release of hormones, which can for example serve as an indication of depression.