Lucien looks tired. The 80-year-old has just returned from a short trip to the Dolomites. He enjoyed the trip, except for the nights. The mattress was too hard, the blanket too warm. Despite the strenuous program, he tossed and turned in bed every night before finally closing his eyes. But even at home, Lucien has had trouble falling asleep for some time. So his doctor prescribed a melatonin spray. The hormone signals to the body that it is time for a good night’s sleep. He can fall asleep better, but sleeping through the night is almost impossible.
He is not alone. In 36 long-term sleep studies involving more than 200,000 people in the Netherlands and Switzerland, 15 percent of people over 65 reported problems falling asleep. About 20 percent said they regularly woke up during the night and had trouble getting back to sleep. These figures were only half as high for people between the ages of 26 and 40.
The fact that sleep changes throughout life is basically normal. While newborns spend an average of more than 16 hours a day in the land of dreams, they spend 12 hours in kindergarten. Teenagers spend 8 to 10 hours in bed, and by the age of 40 that number drops to 7 to 8 hours. After that, sleep duration decreases by about 5 to 10 minutes per decade of life. Thus, the need for nighttime rest seems to be gradually diminishing, even in people who are in the best of physical and mental health.
To investigate the maximum amount of sleep people of different ages can get, we asked both young healthy adults, with an average age of 22, and healthy seniors, with an average age of 68, to participate in a sleep experiment. Their task: to spend 16 hours a day in bed in complete darkness. We then looked at how much they slept during that time. Over the course of the experiment, the amount of sleep leveled off at 8.9 hours for the younger people and about 7.4 hours for the older people. Apparently, that’s all we can do – at least not under laboratory conditions.
But why is that? And why do infants easily sleep two-thirds of the day? It may have something to do with the function of the nocturnal blackout: During this time, important restructuring processes take place in the brain. These include the downregulation of synapses, the connections between nerve cells. This allows the brain to work more efficiently. Unused synapses are even degraded completely. This is important so that there is room to store new information for the next day. In addition, memories are consolidated during sleep: In a sense, they are engraved in long-term memory.
Both tasks are especially important when we have to learn a lot of new things, especially during childhood and adolescence. During this time, the brain undergoes rapid changes day after day. Because the young brain is particularly plastic, it also needs the most sleep during this time. The decrease in sleep duration in old age is therefore not a cause for concern, but simply related to the fact that the learning processes to be carried out continue to decrease due to decades of life experience.
As part of the aging process, sleep typically becomes less efficient. Seniors take longer to fall asleep and wake up more often during the night. Our research shows that 90-year-olds spend a third of their time in bed awake. People under 50 spend just over 10 percent of their time awake. In scientific terms, we are talking about an increasing fragmentation of the night’s rest. One reason for this is that the activity neurons in the hypothalamus become more easily excitable over the course of a lifetime, making us more susceptible to periods of wakefulness during actual bedtime.
Our research has focused on nerve cells that secrete orexins – hormones that control brain activity. We need them to stay awake. That’s why, in the U.S., for example, people are researching sleeping pills that inhibit the orexin system. Some are already on the market. From an evolutionary point of view, these hormones are among the oldest and can also be found in other creatures (e.g. frogs and certain fish). When they are depleted, the result is extreme daytime sleepiness and sudden sleep attacks – a condition known as narcolepsy.
Orexins also seem to have their fingers in the pie. We have found that older people have fewer nerve cells than younger people that produce the body’s own wakefulness stimulants. At the same time, they are much easier to wake up. They therefore need less input to fire and release the neurotransmitter. As a result, older people wake up significantly more often. In addition, we found that the orexin-producing cells lack an important brake system that reduces their excitability. If this brake were also released in younger people, they would spend the night with as many interruptions as seniors.
So seniors spend less time in the land of dreams. In addition, the quality of their sleep is changing. In other words, it becomes lighter. During sleep, nerve cells synchronize their activity – like in a soccer stadium, where fans begin to clap rhythmically before a corner kick. The deeper the sleep, the louder and slower the clapping. Accordingly, the deepest stage of sleep is called slow-wave sleep. When we are young, about 20 percent of our total sleep time is spent in deep sleep. As we age, this percentage decreases significantly, and in some people, it drops to zero. One reason is the loss of gray matter. In a healthy brain, it shrinks a little with age. However, more research is needed in this area.
We can therefore assume that deep sleep decreases with age – more so in men than in women. This starts at the age of 30 and continues exponentially until the age of 60. Beyond that point, we see very little deterioration. So, as with sleep duration, the biggest changes occur in the first half of life.
Another thing we see on a regular basis is that seniors, on average, go to bed a little earlier and get up a little earlier. This shift is partly related to body temperature. This follows a fixed rhythm (regardless of activity level): Late in the evening, our bodies cool down; in the morning hours, they warm up. And when we cool down, we get tired. As we get older, our body temperature drops earlier in the evening, so we start to feel sleepy as early as seven or eight o’clock.
It is still unclear why the body temperature rhythm shifts. An important clock in the brain, the suprachiasmatic nucleus (SCN), has been observed to malfunction with age. This is a pinhead-sized cluster of about 20,000 nerve cells in the hypothalamus. The area is considered the master clock: it makes sure that everything in the body happens at the right time, much like a conductor coordinates the use of instruments. Over the years, however, its signals become weaker and fuzzier. This increases the risk that some processes will go out of sync.
The SCN orients itself to sunlight. Special sensors in our eyes, the light-sensitive ganglion cells, help it to do so. These form a third group of photoreceptors, along with cones and rods. From there, light signals travel to the hypothalamus. This prevents our master clock from moving forward or backward over time. It synchronizes with the natural day-night rhythm. This means that the SCN needs an external timer – and the strongest one we have is light.
Over the years, however, the lens of the eye turns yellow and transmits less blue light, to which the ganglion cells are particularly sensitive. This further weakens the day-night rhythm, which is already not very pronounced. Pathological changes such as cataracts, a clouding of the lens, can also disrupt nighttime sleep. Normally, in the light, the SCN prevents the pineal gland in the midbrain from producing melatonin. In the dark, the body is flooded with the hormone. This causes a feeling of fatigue.
This is why it is often prescribed as a sleep aid. As we age, however, the fluctuations in melatonin levels diminish – partly because the internal clock stops ticking so loudly anyway, and partly because, as described above, the incoming impulses are weakened by the cloudy lenses. This can blur the distinction between day and night and make sleep more polyphasic. Sleep is no longer concentrated between 10 p.m. and 7 a.m., but distributed throughout the day.
Changes in sleep do not affect everyone equally. This can be seen, for example, in the decline in sleep efficiency. People who fall asleep and stay asleep well in their younger years are more likely to do so as they age. After all, one-third of all men and women fall into this category. Sleep should therefore be seen as part of the personality, because those who are restless sleepers in old age were very likely to be restless sleepers in their younger years.
For some time, however, Lucien’s restlessness has been exacerbated by a medical problem: In recent years, he has had to go to the bathroom more often at night because of prostate problems. In fact, it is often accompanying symptoms that exacerbate age-related changes in nighttime sleep patterns, sometimes to the point of causing serious sleep disturbances. In addition, there is pain and increased use of medications that can interfere with sleep, such as anti-inflammatories, beta-blockers, cortisone, or antidepressants.
Another condition that older people face more often than younger people is sleep apnea. It occurs when the tongue and soft part of the palate rest on the airway during sleep, blocking it. Sufferers can’t breathe: for 10, 30, sometimes even 60 seconds. The oxygen level in their blood drops significantly during this time. At some point, their shortness of breath becomes so severe that they startle briefly and inhale explosively. In severe cases, this can happen every few minutes. After the age of 65, the risk of obstructive sleep apnea increases. Reasons for this include a decrease in muscle tension in the upper airway and obesity.
Lucien has no problems breathing at night. He also knows about another disorder from hearsay: restless legs syndrome. Women in particular suffer from restless legs. The frequency increases with age, but the link is not yet fully understood. The cause of restless legs is often iron deficiency, which can be caused by chronic bleeding, for example from stomach ulcers. Various medications can also cause the syndrome. The typical tingling sensation and uncontrollable urge to move occur mainly in the evening hours. They make it difficult for people to fall asleep.
Prolonged and severe sleep deprivation requires treatment because it can have serious consequences: Falls, impaired concentration and memory, and even dementia in the long term. In 2021, Séverine Sabia’s team at the University of Paris caused a stir with an alarming discovery: People who consistently sleep less than 6 hours a night are 30 percent more likely to develop a neurodegenerative disease than normal sleepers.
In addition, during sleep, the brain becomes a waste disposal system. This means that it transports the waste accumulated during the day in the form of damaged proteins, acid products, and other substances through the nose, liver, and stomach to the intestines, where it is then excreted from the body, e.g., through urine. In total, about 7 grams of waste are produced, of which about 1 gram can be removed per hour. This gives our brain about 7 to 8 hours to clean up and prepare for the next day. Without sleep, these waste products quickly turn into pathogens that lead to neurodegenerative diseases such as dementia and Parkinson’s.
So what can you do about sleep deprivation? Simple measures are often enough. If you have obstructive sleep apnea, losing weight and avoiding alcohol usually helps. Otherwise, a special sleep mask can help. Effective medications are now available for restless legs syndrome. In addition, people with sleep problems should avoid coffee, tea, cola, and alcohol as much as possible, but especially after 5 p.m. And in general, you should only drink a little a few hours before going to bed so that the bladder does not press too hard during the night.
You can also help your internal clock, which is ticking ever more silently, by getting outdoors on a regular basis. Getting outside for an hour every day, regardless of the weather, is not only good for your cardiovascular system: brightness and activity stimulate the SCN to swing the bat a little harder. Because light slows the release of melatonin, it helps combat daytime sleepiness. Sleep is thus more concentrated in the night hours. Those who are less mobile can help themselves to a light shower, i.e. a strong daylight lamp. It works best when mounted on the wall above your head – the light-sensitive photoreceptors are located primarily at the bottom of the eye and are most stimulated by light coming from above.
An age-old home remedy has also proven effective: a warm foot bath in the evening. Warm water stimulates blood circulation. The extremities then release heat into the environment through the blood, lowering the body temperature. From a physiological point of view, this is the strongest sleep stimulus we have. On the other hand, it is difficult to fall asleep with cold, poorly circulated feet.
Adequate sleep pressure is also important for a good night’s sleep: people who are physically active during the day sleep better at night. Mentally challenging situations have a similar effect. Therefore, it is important to keep the mind active, for example by meeting other people.
In some circumstances, medication is appropriate. In the case of insomnia, however, I advocate the use of cognitive behavioral therapy. It is simple, effective, and most importantly, it helps you sleep better in the long run. There are only a few rules to follow. These are
Many people have exaggerated ideas about what their sleep should be like. Behavioral therapy can help with that, too. The fact that sleep becomes more restless with age is not a surprise – nor is it a catastrophe. If we wake up once or twice during the night, that’s as it should be. After all, the aging process is not only visible in the hair.