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Sleep undergirds every aspect of our physical and mental health, which we need to support now more than ever. Cultivating healthy sleep behaviors during this nightmarish time can get you closer to the sleep of your dreams.
Healthy sleep behaviors support the two physiological processes that interact to foster consolidated episodes of sleep at night and wakefulness during the day: the homeostatic drive (which regulates pressure to fall asleep) and the circadian drive (which determines our daily rhythm of feeling alert).
The two-process model
As the drive for sleep increases during the day, our circadian drive for alertness also increases, which stimulates wakefulness during the day despite the rising pressure to fall asleep. At night, when the circadian drive for alertness falls but the homeostatic drive for sleep rises, we can fall asleep. In the morning, awakening occurs when the rising circadian drive for alertness surpasses the homeostatic drive for sleep. Alignment between these two processes promotes proper functioning during the day and aids sleep onset and maintenance at night.
The homeostatic sleep drive: Your body’s “hunger” for sleep
The homeostatic sleep drive refers to the increased propensity to sleep with more time spent awake (sleep-wake homeostasis). Increased time spent awake means more accumulated “sleep pressure” to fall asleep. You can think about this process like hunger: The longer you go without eating, the hungrier you get, the more you need to eat, and the more you will eat when given the chance.
Homeostatic sleep drive works similarly: The longer you stay awake, the sleepier you get, the more you need to sleep, the longer and deeper you will sleep given the opportunity.
Practical ways of supporting healthy sleep homeostasis:
1. Exercise. If you had $100 and spent $50, you wouldn’t have those $50 later. You can think about energy expenditure and sleep similarly: The more energy you expend throughout the day, the less energy you’ll have later, which typically translates into better sleep. Exercising during the day may promote sleep by acting on the homeostatic sleep drive via sleep-promoting compounds (e.g., adenosine) and other physiological processes.
2. Restrict your time in bed. Limiting time in bed helps to build sleep pressure. The longer you stay awake and out of bed, the “hungrier” your body gets for sleep.
3. Avoid napping. Daytime napping can reduce the homoeostatic buildup of sleepiness. If you must take nap, keep it brief (15-20 minutes) and consistent.
4. Limit afternoon caffeine. Caffeine opposes sleepiness because it binds to receptor sites involved in accumulating sleep pressure. It also has a half-life of about 5 hours, meaning that even after 5 hours, 50% of the dose remains active. For healthy sleep homeostasis, consider having your last cup in the afternoon.
The circadian drive: The body’s biological clock
The circadian drive refers to the variations in biological processes that the internal clock regulates to promote arousal at certain times of day. It activates or inhibits our urge to sleep throughout the roughly 24-hour cycle (circa diem = “about a day”). Without this process, we would sleep haphazardly according to the duration of our wakefulness.
Trying to initiate sleep at a suboptimal circadian time, such as in the case of shift workers who sleep during the day when the circadian drive for arousal increases, produces objective and subjective impairments in sleep quality, architecture, and consolidation that may adversely affect overall health.
Factors that influence the circadian drive
External and endogenous cues known as zeitgebers, a German word meaning “time-givers," work to synchronize our biological clock:
1. Light. In humans, darkness promotes sleep, light promotes wakefulness. Light signals sent from the eye to the brain help to regulate our biological rhythms. Sunlight plays a big role in entraining the circadian rhythm, so consider starting your day with 10-15 minutes of sunlight. The light emitted from artificial sources (e.g. phones, tablets, televisions) can also impact our circadian system.
2. Hormones. Consider ending your day by reducing face time with blue light-emitting devices one to two hours before bed. Sleep coincides with a natural dip in cortisol and the peak of melatonin, a drowsiness-promoting hormone. Darkness promotes melatonin’s production, light interrupts it —but blue light especially may hijack deep sleep.
3. Temperature. A nocturnal decline in core body temperature helps the body to initiate and maintain sleep. Combined with keeping the bedroom cool (somewhere between 60-67 F), passive body heating 60-120 minutes before bed may hasten sleep onset because it reduces core body temperature. Refraining from other thermogenic activities before bed, such as eating heavy meals, drinking alcohol, or exercising vigorously can also help support the circadian drive.
4. Other cues. The body rewards regularity. Keeping a regular, daily wake time (even on weekends) synchronizes our body clock and can optimize our physical, psychological, and cognitive health. Worried about follow-through? Consider setting an alarm clock and placing it across the room so that when it sounds, you have to get (and stay out) of bed to turn it off.
Take-home messages
Sleep happens when increasing sleep pressure, as regulated by sleep homeostasis, coincides with a reduction in the endogenous physiological drive for arousal, as regulated by the biological clock.
Changing waking behaviors to align the homeostatic and circadian drives facilitates sleep onset, promotes sleep consolidation, and optimizes sleep quality and daytime functioning. Behavioral treatments for insomnia, including Brief Behavioral (BBTI) and Cognitive Behavioral (CBT-I) therapies aim to impact and align these processes.
Talk to your healthcare provider if you experience any impairment or distress during wakefulness because of your sleep concerns.
This piece also appeared as an infographic created alongside Ari Shechter, Ph.D., of Columbia University.
