How Sleep Changes with Age
Did you know that our sleep changes over the course of our lives? A mis-understanding of normal age-related changes in sleep can lead to over use of sleeping medications and unnecessary worry. Read on to learn what types of changes to our sleep are normal as we age.
Over the course of our lives, from infancy to old age, every aspect of our physiology changes. For instance, let’s look at what happens to our hair as we age: the hair on a newborn baby may fall out a few weeks after birth, then slowly grow back, then darken as the child ages, thin out a bit as he or she reaches adulthood, then slowly turn gray, then white and increasingly thin. Our joints change with age, as does our metabolism, our fat to muscle ratio and our skin. Sleep, of course, is no exception.
Changes in the Composition of Sleep
Figure 1, above, shows how our total sleep duration and percentages of each sleep stage change over our lifespan. The total duration of sleep is the combined amounts of stages 1, 2, SWS (slow wave sleep, also called “deep sleep”) and REM (rapid eye movement) sleep. The first thing to notice is that our total sleep duration declines over time. The most dramatic decline is from childhood to our mid-30s, but there continues to be a slow decline in sleep duration over the rest of our lifespans. Nevertheless, the total amount of time that most of us spend in bed (total sleep duration plus WASO and sleep latency), remains roughly stable once we reach our mid-30s, only declining slightly in our 80’s. Taken together, these changes mean older people will spend the same amount of time in bed as when they were younger, but more of that time will be spent awake and in lighter stages of sleep.
Changes in Sleep Structure
Figure 2 helps us to better understand how these changes actually look across the night. Figure 2 shows a typical “hypnogram” (sleep graph) at 3 different points in our lives. Humans sleep in cycles lasting around 90 minutes, with a brief awakening occurring after each sleep cycle. Each 90-minute sleep cycle starts with our brain being awake. Then we progress through the different stages of sleep: Stage 1, Stage 2, Stage 3, Stage 4 (stages 3 and 4 are also known as slow wave sleep, which is the deepest stage of sleep) and REM (Rapid Eye Movement sleep, the stage of sleep where we tend to have vivid dreams). After each sleep cycle we wake up briefly (we may or may not be aware of this awakening), then fall back to sleep and into the next cycle.
In childhood the awakenings between sleep cycles are extremely short and typically not remembered. Additionally, large amounts of slow wave sleep occur, even towards the end of the night. The net result is that children sleep very deeply with very little time spent awake during the night.
As we reach our mid-30’s, we start to have more wakefulness during the night and the deepest parts of sleep typically only occur in the first half of the night. This means that an adult may be aware of waking up once or twice during the night. An adult may also notice that their sleep feels less deep in the second half of the night, particularly just before their natural wake up time.
As we move into old age, we spend a larger and larger percentage of the night awake and our sleep is also significantly less deep than earlier in our lives. The net result is that an older person may feel that they only obtained a few hours of real sleep and were awake the rest of the night. If you look at the hypnogram labeled “elderly”, you can see that this impression is not exactly correct: the older individual is sleeping until the end of the night and does still have all the stages of sleep, but the sleep overall is much more fragmented than when that person was younger. The sleep during last portion of the night in an older individual is often a mixture of wakefulness, dreams and light sleep during which that individual will have some awareness of their surrounding environment. Most people think of sleep as a state where we lose all awareness of our surrounding environment, but more and more research is suggesting that it is actually possible for a small part of the brain to be awake with some awareness of its thoughts and surroundings while the rest of the brain is asleep. Additionally, when our sleep is repeatedly disrupted by environmental sounds or frequent natural awakenings, our brain only remembers the times when it woke up and erroneously jumps to the conclusion that we were continuously awake. Reassuring an older person that they are actually getting sleep in the second half of the night is often helpful in reducing their worry about their sleep.
Changes in Sleep Timing
Figure 3 shows how our preferred timing of sleep changes with age. Children and older adults naturally go to bed earlier and wake up earlier than teenagers and young adults. We see this change in sleep timing over the lifespan not only in cultures that use artificial lighting and electronic screens, but also in cultures living without electricity or modern technology. The theory behind these age-related changes in sleep timing is that for a tribe of humans living together it would have been advantageous to have someone in the tribe awake at every time of night. Additionally, the “fittest” individuals should naturally be able to stay awake at the highest risk time of night (the first half of the night) to protect the rest of the tribe. In the time of our ancestors, the “fittest” individuals were the people in their teens and 20s. In the second half of the night, the oldest individuals would be lightly asleep and then wake up early and they would be able to alert the rest of the tribe of any potential threats. The net result of these age-related changes in sleep timing is that teenagers find it difficult to go to sleep early and older adults find it difficult to sleep in. In a study looking at preferred sleep timing over the lifespan in modern Europeans, the average preferred timing of sleep in at age 20 was 2 hours later than at age 50 (Figure 3, above).
Implications of Age-Related Sleep Changes
Is the lighter sleep of older individuals inferior to the deeper sleep of younger individuals? There is some debate amongst sleep researchers and clinicians about whether artificially deepening sleep in old age can improve cognition, but so far this has not been proven. We know for sure that artificially deepening sleep in old age with sleeping medications does not prevent dementia and actually seems to worsen memory and balance compared to individuals who do not use sleeping medications. The latest research attempts to artificially deepen sleep are therefore trying to do so without medications, using techniques such as pink noise and gentle rocking of the bed. We know that even cognitively intact older individuals have lighter, more fragmented sleep than when they were younger. Older individuals are also more resilient to the effects of a night without sleep, showing less of a decline in their cognitive performance the following morning compared to younger individuals.
In summary, sleep, like everything else in the human body, changes profoundly across our lifespan. It can be completely normal for an older individual to get tired earlier in the evening and wake up early in the morning. It can also be normal for an older individual to be aware of being awake for a much larger percentage of the night than when they were younger and to feel that their sleep is much lighter than when they were younger. I hope understanding these normal age-related sleep changes can reassure both physicians and patients and reduce the prescribing of unnecessary and potentially harmful sleeping medications.
Regardless of your age, there are things that you can do to maximize your sleep quality. These include exercising regularly, getting sunlight (particularly in the morning), eating a healthy diet that minimizes added sugars and processed foods, keeping active socially and continuing to engage in activities that stimulate the mind. Keeping a regular sleep schedule that allows for 7–9 hours in bed each night is also important. Remember as you age that those 7–9 hours in bed will not all be spent asleep and this is ok.
