We humans are active during the day and rest at night. Our good physical and mental functioning is very dependent on this alternation of periods of daytime activity and nighttime recovery.
However, although essential to our health, this sleep/wake rhythm is not immutable: as we age, sleep, like any other physiological function, changes .
How ? How to ensure despite everything to keep a quality rest?
We now know that sleep is involved in many physiological processes . For example, it is involved in the functions of cell and tissue regeneration, brain and immune development. It also plays a role in memory consolidation processes.
When it is degraded, we observe a progressive deterioration of these different processes , which has a negative impact on the quality of life: increased daytime sleepiness, disturbance of cognitive functioning, such as memory or attention problems. Chronic poor sleep will make us more irritable, more anxious, more easily ill, and more prone to weight gain .
Sleep is broken down into several phases, which constitute a cycle: light slow sleep, deep slow sleep and paradoxical sleep. Light slow-wave sleep corresponds to an intermediate stage between calm wakefulness and sleep, and accounts for approximately 50% of total sleep time. Slow-wave sleep accounts for about 25% of total sleep time; it is the most physically restorative sleep. Finally, paradoxical sleep is driven by our dreams and represents 20 to 25% of total sleep time. It owes its name to the contrast between intense brain activity, comparable to that observed during wakefulness, associated with an absence of muscle tone.
Each of these phases plays a specific role in the process of recovery and preparation for the upcoming wakeful period . However, with advancing age, the temporal organization of sleep changes, and its quality decreases are observed.
Sleep is not immutable
While in young adults, the different stages of sleep follow one another in a stable fashion during the night, in the elderly, sleep is fragmented.
Among other things, we note an increase in the time it takes to fall asleep, a reduction in the time spent in deep slow-wave sleep and an increase in nocturnal awakenings associated with difficulties in falling back to sleep . The amount of deep slow-wave sleep and REM sleep decreases, meaning sleep is lighter and less restorative.
Therefore, it is not surprising that more than half of the elderly report at least one sleep disorder , which translates into a tendency to sleepiness during the day. Accumulated fatigue is not without consequences on cognitive functions, mood and physical condition , and it can also have a deleterious effect on autonomy.
The possible consequences of a chronic lack of sleep should therefore not be ignored. They can be diverse: permanent fatigue, concentration problem, gloom, melancholy, irritability or even reduced immune resistance.
Why does sleep get harder with age?
Every sleep problem is different, and several factors may explain the higher frequency of occurrence of sleep difficulties with aging.
The existence of health problems may be one explanation. Indeed, taking certain medications can cause sleep disturbances. The emotional state can also be involved: anxiety, stress, depression or ruminations degrade the quality of sleep. At the time of retirement, the change in lifestyle and social references can also have consequences.
Furthermore, it should be noted that “normal” aging is accompanied by a desynchronization of the biological clock linked to the reduction in the plasticity and adaptive capacities of the body of the elderly subject . This disorder can result in an earlier bedtime and an earlier awakening in the morning. The decrease in the level of physical activity and the increase in sedentary lifestyle can also degrade the quality of sleep. Finally, as we get older, the risk of the onset of sleep pathologies (such as obstructive sleep apnea syndrome) increases.
Light, a solution to maintain quality sleep?
Complaints associated with age-related sleep decline often result in the prescription of sleeping pills. However, their side effects can alter the quality of life of the elderly, by reducing mental abilities, deteriorating motor coordination and increasing the risk of falls .
To limit these effects and improve sleep, non-drug therapies can be put in place, such as light therapy , which can be associated with the practice of physical activity .
Light is indeed considered the most powerful synchronizer for the biological clock and allows us to maintain and reset our rhythms, for example to set our bedtimes and wake up times . It also regulates cycles that we don’t think about or that most people ignore: the rhythms of mood and cognitive performance, including thinking and attention skills. Thus, depending on the time of day and the quality of our previous night, we are more irritable, or on the contrary, more attentive and efficient in tasks requiring intense thought .
These rhythms vary from one individual to another, but one thing is common: when our clock is out of order, for example due to aging, these rhythms are disturbed and alter our mood and our intellectual capacities. To combat this process, studies have shown that exposure to sunlight or artificial light can be beneficial. The light improves the sleep/wake rhythm while reducing the symptoms of depression . It can also improve the cognitive performance and emotional state of the elderly .
Exposure to light also has positive effects on the immune system and stimulates the production of our body’s defences. In general, to improve these parameters, it is recommended to expose yourself to at least half an hour in the morning every day at an intensity of 10,000 lux . As an indication, in direct sunlight the light intensity varies from 50,000 to 100,000 lux and that of a cloudy sky is between 500 and 25,000 lux. For artificial lighting, it will be necessary to ensure that you have the appropriate equipment , such as a light therapy lamp.
Light therapy is a treatment for sleep-wake rhythm disorders and can be used in situations such as jet lag, night or shift work, advanced phase syndrome, or blindness. Concretely, it is a question of exposing oneself to the light of high intensity lamps for a recommended period . Be careful though: if the exposure period is not practiced at the right time (too early or too late in the day), sleep disturbances may occur. Furthermore, this type of therapy may not be recommended for patients with an ocular pathology or treated with photosensitive drugs. Therefore, the opinion of an ophthalmologist is recommended.
The benefits of physical activity also extend to sleep
Physical activity is known for its many benefits: improved physical condition and cardiovascular health, prevention of chronic pain, improved immune function, anxiolytic and antidepressant effects. But we know perhaps less that it also improves the quality of sleep .
Indeed, physical activity plays the role of synchronizing the sleep-wake rhythm: it reinforces the contrast between periods of wakefulness, when one is supposed to be active, and periods of rest and sleep, when one is supposed to sleep. In addition, exercise increases “good” fatigue, while decreasing the anxiety that tends to fuel nighttime ruminations at bedtime.
In general, elderly people who practice a rather predominantly aerobic physical activity – that is to say an activity inducing an increase in heart rate and respiratory rate – such as Nordic walking, hill climbing, cycling, hiking, etc. – report that they fall asleep faster, sleep longer and have better quality sleep . The World Health Organization also recommends that older people practice at least 150 to 300 minutes of moderate aerobic physical activity per week.
Other tracks being evaluated
Research is progressing and other non-drug treatments are developing. One of them in particular deserves our full attention, it is vestibular stimulation.
The vestibular system is located in the inner ear and allows us to feel the accelerations experienced by our head. It allows us to know how it is tilted, what tells us about our position (standing, lying, on one side, etc.), as well as how it moves, and with what intensity.
Exposing the inner ear to a mild electrical current stimulates the vestibular system artificially. This vestibular stimulation has already shown beneficial effects on balance , mood (Pasquier, 2019) and sleep , which are three functions that are altered with advancing age. Although this track still requires in-depth research, it could quickly become an essential new therapy.
While waiting for this confirmation, to have a good sleep, it is already strongly recommended to expose yourself to enough light and to practice regular physical activity, whatever your age! If ever this proves to be insufficient, do not hesitate to consult a doctor, who will determine the relevance of resorting to other approaches, such as psychotherapy, or will consider analyzes to detect possible pathologies.
Author Bios: Emma Milot is a PhD student in Sciences and Techniques of Physical and Sporting Activities – COMETE U1075 INSERM/Unicaen Laboratory and Marc Toutain is also a PhD student in Sciences and Techniques of Physical and Sports Activities – COMETE U1075 INSERM/Unicaen Laboratory both at the University of Caen Normandy