Effects of Sleep on our Health

Sleep is unquestionably vital and universal function for humans (1). However, sleep problems has been a growing issue in recent years to global public health. Poor sleep quality is associated with negative psychological consequences such as anxiety and depression (2), motivation (3-5), altered cognitive functioning (6), aggression (7), and attention-deficit/hyperactivity disorder (8). In addition to this, it also has a negative impact to our physical health such as higher levels of body mass index (8,9) type 2 diabetes (10), chronic pain (11) hypertension (12), cardiovascular disease and cancer (3-5).

There has been a considerable amount of evidence showing the lack of sleep duration in both children and adults that lead to the increased risk of obesity. Experimental studies done with healthy adults who were placed under sleep restriction have shown alterations in metabolic profiles (eg. cortisol, insulin, leptin and ghrelin) which are associated with sleep loss. These metabolic alterations resulted in insulin resistance, increased hunger, decreased satiety and increased sympathetic nervous system activity (13). These alterations in turn resulted in consuming a higher amount of calories and less exercise (14-17).

Indisputably, good sleep is essential to good health. Yet in our modern society, having regular good sleep is not necessarily common amongst most of us. Insomnia has became one of a common concern of health (18) and a rising concern especially during the pandemic across the globe. The definition of insomnia is characterised by the perception of poor-quality sleep caused by the difficulty to initiate sleep/stay asleep, resulting in daytime dysfunction (19).

What are some Factors that Affects Sleep?

Screen time

Shorter sleep duration has been related to our screen time (20). The most noticeable factors that contributes to this relation are night time screen use and the increase of social networking in the 21st century (21). By delaying sleep timing on weekdays and playing catch-up sleep on weekends delays the signal for the biological night (ie. Melatonin production) and depletes residual sleep pressure (22). Also, by delaying our sleep timing and waking later on weekends compared to weekdays reflects the biology of our circadian rhythm within and is a direct response of the body's insufficient weekday sleep.

Not only so, the use of multiple electronic devices contributes to the increase in sleepiness during daytime and less sleep at night (23-27). This is because the light produced by the various electronic devices may disrupt our circadian rhythms, suppressing melatonin and resulting in the inability to fall asleep at a reasonable time (21).This has been backed by recent studies that have shown circadian rhythms can be altered by exposure to relatively low-intensity light (28,29) and suppress nocturnal melatonin secretion (30).

On top of all, the use of media may also cause an increase in emotional, physiologic and mental arousal that disrupts sleep (21). One study has shown that interactive video game in the evening found a decline in prolonged sleep latency, verbal memory performance and an increase in light sleep (31) while another study showed subjects sleepiness was lower, rapid eye movement (REM) sleep was shorter and sleep latency was longer after playing video shooting games (30).

Stress

Psychosocial stress and sleep have been associated in numerous studies (32). In our busy lifestyles, the stress we shoulder on can unconsciously trigger cognitive arousal (ie. worry, anxiousness, vigilance) and physiological arousal (ie, increased blood pressure or heart rate, stomach upset), both of which disrupts sleep initiation and maintenance. Psychological stress, particularly when present at bedtime, is one of the primary mechanism that disrupts sleep as it increases psychophysiological arousal, resulting in the increase of sympathetic arousal that causes wakefulness throughout the night and less restorative sleep (33).

Caffeine

Caffeine can be a happy place in the day and a dark place at night. A single dose of caffeine has a half-life of 3-7 hours in our bodies and causes plasma levels to peak approximately 30 minutes after consumption. Caffeine also causes blockade of adenosine receptors in the basal hypothalamus and forebrain that keeps us awake (34,35). Nevertheless, these effects varies by individual differences in metabolism, sensitivity and accumulation(34,35) while the half-life of caffeine also remains active longer with age (36). Therefore, it is important to keep in check the timing of your caffeine intake well in order to allow sufficient time for caffeine to be dissipated and enjoy a well deserved quality sleep at the end of the day.

In summary, the combination of modern lifestyles and social obligations in the current society do have an impact and disrupts the opportunities to obtain adequate sleep, in a way.

How can we Improve Sleep Quality?

Create your own sleep hygiene, your way

- Regular bed and/or wake times creates maximum synchrony between circadian rhythms, physiological sleep drive and nocturnal sleep episode (37). Circadian system and homeostatic sleep drive work together to promote stable patterns of sleep and wakefulness (38). Sleep are often worsened when the primary sleep episode varies from time to time (ie. sleeping earlier or sleeping later) from rotating shift work or jet leg (39). This irregular bed and wake-times causes desynchrony between circadian rhythms and sleep-wake timing, thereby increases in inter-night variability in sleep timing.

- Regular exercise may improve sleep through its effects on arousal, adenosine levels and body temperature (40). In one study, acute exercise on adults with insomnia have showed that an acute bout of moderate-intensity aerobic exercise performed in the late afternoon did improved substantially in PSG- and diary-assessed SOL and TST on the subsequent night, whereas neither high-intensity aerobic exercise/moderate or high intensity resistance exercise altered sleep (41). Overall, amassed research do suggest that exercise can be a useful behavioral approach for reducing sleep disturbance.

Sleep for Better Performance

A large quantity of research have accumulated compelling evidence of how sleep supports the consolidation of learned information into long-term memory (42,43). Studies have shown an increase in occurrence of spindles during a period of sleep (either a full night or a daytime nap) after learning as to increased retention performance (44-48) Spindle activity have been found to have association with visual declarative memory (49), verbal (46,-48,50- 52) and motor procedural memory (53-58).

Interestingly, NREM-rich sleep which happens during the first part of the night is responsible for declarative memories, while REM-rich sleep which happens the second half of the night is responsible for non-declarative/implicit (eg.procedural) memories (59-63). More so, spindles occurring in light NREM sleep are related to procedural motor learning (64,65).

Motor learning and a reorganisation of neural activity between brain structures often happen during sleep related procedural memory consolidation. Activity recruited during training in the rostrodorsal striatum (associative area) on motor sequence tasks are shown to be subsequently transform to activity in the caudoventral subregion of the striatum (sensorimotor area) post-learning (66,67). This reorganization was associated with spindle-related reactivation of the putamen happens during sleep, of which is also related to overnight gains in performance. (66). The coherence(functional binding) of cortical and subcortical brain activity during sleep spindles was related to post-learning gains in motor learning consolidation (67).

All in all, these are just some factors that may affect or contribute to your quality of sleep. There will always be times where we'll be facing some factors that can't be controllable (ie, rotating shift work or taking care of a child at night) and that is alright.

Take control of what is controllable and let go of what you can't, work with what you have and make the best out of it.

At the end of the day, health is the work of balance.

Have a good night sleep y'all! <3

With love,

Ashley

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