The science of sleep
The science of sleep: The body's role, why we need it, and the consequences of sleep deprivation
Posted: March 2025
Author: Hannah Leech, Naturopath | Medical Herbalist | BNat, mNMHNZ
Sleep is an essential part of being human, it's a biological necessity. From restoring cognitive function and clearing toxins from the brain, to strengthening the immune system, sleep plays a crucial role in maintaining overall health and well-being. Sleep deprivation has been linked to increased risk of many diseases including Alzheimer's, cancer, depression, heart disease, and strokes.1
Several structures are involved in sleep, including the hypothalamus, suprachiasmatic nucleus (SCN), brainstem, thalamus, cerebral cortex, pineal gland, basal forebrain and the amygdala.1
Each of these brain structures works together to receive signals, gather information and promote sleep. The SCN, found in the hypothalamus, collects information from the eyes about light exposure, allowing the body to know if it is time to sleep or to be awake. It is difficult for the body to regulate sleep when this part of the brain is damaged, and people can sleep randomly throughout the day as they can’t match the light signals to their circadian rhythm (sleep/wake cycle).
The sleep cycle is controlled by our body's internal clock, known as the circadian rhythm, which is managed by the SCN. This rhythm also helps control the release of hormones including melatonin, to induce sleep, and acetylcholine (ACh), dopamine and other hormones to keep us awake during the day.
Even though we know sleep is important for humans, scientists are still unsure exactly why it's so necessary. We don’t fully understand all the functions of sleep, and it’s subject to ongoing research. Some ideas about why we sleep include:
- Helping the brain develop
- Helping us learn and remember things
- Allowing the brain to "forget" unnecessary information
- Supporting our thinking abilities
- Clearing away waste products that build up in the brain while we’re awake
- Saving energy for the body.2
Stages of sleep
While there are two main stages of sleep, REM (rapid eye movement) and non-REM, research has found there are three stages of non-REM sleep.2 The cycles are depended on the level of brain waves and neuronal activity. These cycles are constantly happening during the night with the number of cycles depending on how long an individual sleeps and average 90 minutes.2
Non-REM occurs first and is the segway from wakefulness to sleep. The first stage is a light form of sleep just after being awake, where the body is slowly slowing down your heart rate, breathing rate and brain activity. The second stage is where people stay the longest in the sleep cycle, it is still light sleep, but the body temperature drops, eye movement stops, and the body relaxes further. Stage three is deep sleep with longer periods happening in the first part of the night and it is the stage that provides the “wake up feeling refreshed and alert” in the morning.
REM sleep where an individual’s eyes move around behind their eye lids and brain activity is seen as similar to that of being awake. Breathing, heart rate and blood pressure increase. This stage is where most of dreaming occurs, with the brain stem sending out signals to relax muscles essential for body posture and limb movements, so that dreams aren’t acted out. After a period of time the cycle starts again and transitions back to non-REM.
Sleep loss
There are many causes of sleep loss that come under two categories Lifestyle such as shift work, irregular sleep cycles or jet lag, and other includes sleep disorders such as insomnia, circadian rhythm disorders and narcolepsy.3
Though the cause might differ, the symptoms are relatively the same. These include, excessive daytime sleepiness, reduced alertness, slow reaction times, reduced cognitive ability and impaired logical reasoning, mood changes, including irritability and brief daytime sleep periods, called microsleeps.3, 4
The cumulative effects of sleep loss and sleep disorders have been associated with multiple health consequences and effects on the cardiovascular, endocrine, immune, and nervous systems. The health consequences include obesity, diabetes, impaired glucose tolerance, cardiovascular disease and hypertension, anxiety, depression and substance abuse and addiction.4
Herbs to aid sleep
Common herbs to aid better sleep include Lavender (Lavandula angustifolia), Valerian (Valeriana officinalis), Chamomile (Matricaria chamomilla), Passionflower (Passiflora incarnata), Baical Skullcap (Scutellaria baicalensis) and Withania (Withania somnifera).
Lavender (Lavandula angustifolia) contains volatile oils that are known to interact with the olfactory nerve and reach the brain, helping alleviate insomnia, irritability, restlessness, and poor sleep. It can improve sleep quality in individuals with insomnia and promote deeper sleep in those without sleep disturbances.5 The weekly therapeutic dosage range is 15-30 mL.
Valerian (Valeriana officinalis) aids sleep due to the presence of valerenic acid. This increases GABA levels in the brain by preventing its reuptake and enhancing its transport. This action helps facilitate sleep and makes it easier to fall and stay asleep at night.5 The weekly therapeutic dosage range is 15-50 mL
Chamomile (Matricaria chamomilla) is a potent nervous system relaxant that helps alleviate insomnia and reduce nervous tension. It has been shown to improve sleep, particularly by decreasing the frequency of awakenings during the night and helping individuals stay asleep.5,6 The weekly therapeutic dosage range is 20-60 mL
Passionflower (Passiflora incarnata) is a mild sedative, anxiolytic, and hypnotic herb known for improving sleep quality. It helps reduce irritability and restlessness, common obstacles when trying to fall asleep.7 The weekly therapeutic dosage range is 15-40 mL
Baical Skullcap (Scutellaria baicalensis) contains a plant derived melatonin, baicalin, which has two opposite effects on sleep. It reduces deep sleep during the day and increases deep sleep and REM sleep at night. These effects might be caused by baicalin blocking the action of an immune protein, IL-1, during the day and boosting GABA receptor activity at night. 8, 9 The weekly therapeutic dosage range is 30-60 mL
Withania (Withania somnifera). Withania’s alkaloids contain sedative actions that help encourage sleep and decrease insomnia. It is also an adaptogen herb helping decrease stress levels and make it easier to sleep at night. 9 The weekly therapeutic dosage range for standardised Withania is 10-25 mL
Hops (Humulus lupulus) is known as a sedative and hypnotic herb, which is understood to be mainly due to its bitter resins. One study found it effectively reduces nighttime activity in the circadian rhythm. (10) The weekly therapeutic dosage range is 10-25 mL
References
1. National Institute of Neurological Disorders and Strokes. (n.d.). Brain basics: Understanding sleep. National Institute of Neurological Disorders and Stroke. Retrieved March 10, 2025, from https://www.ninds.nih.gov/health-information/public-education/brain-basics/brain-basics-understanding-sleep
2. Patel, A. K., Reddy, V., Shumway, K. R., et al. (2024, January 26). Physiology, sleep stages. In StatPearls [Internet]. Treasure Island (FL): StatPearls Publishing. Available from https://www.ncbi.nlm.nih.gov/books/NBK526132/
3. Colten, H. R., & Altevogt, B. M. (2006). Sleep disorders and sleep deprivation: An unmet public health problem. Institute of Medicine (US) Committee on Sleep Medicine and Research. National Academies Press. Available from https://www.ncbi.nlm.nih.gov/books/NBK19961/
4. Sleep Foundation. (2025). Sleep deprivation: Symptoms, treatment & effects. Sleep Foundation. Retrieved March 10, 2025, from https://www.sleepfoundation.org/sleep-deprivation
5. Fisher, C. (2018). Materia Medica of Western Herb. . VitalSource Bookshelf 10.1.0.
6. Kazemi, A., Shojaei-Zarghani, S., Eskandarzadeh, P., & Hashempur, M. H. (2024). Effects of chamomile (Matricaria chamomilla L.) on sleep: A systematic review and meta-analysis of clinical trials. Complementary Therapies in Medicine, 84, 103071. https://doi.org/10.1016/j.ctim.2024.103071
7. Ngan, A., & Conduit, R. (2011). A double-blind, placebo-controlled investigation of the effects of Passiflora incarnata (passionflower) herbal tea on subjective sleep quality. Phytotherapy Research, 25(8), 1153–1159. https://doi.org/10.1002/ptr.3400
8. Chang, H. H., Yi, P. L., Cheng, C. H., Lu, C. Y., Hsiao, Y. T., Tsai, Y. F., Li, C. L., & Chang, F. C. (2011). Biphasic effects of baicalin, an active constituent of Scutellaria baicalensis Georgi, in the spontaneous sleep-wake regulation. Journal of ethnopharmacology, 135(2), 359–368. https://doi.org/10.1016/j.jep.2011.03.023
9. Braun, L., Cohen, M. (2014). Herbs and Natural Supplements: An evidence-based guide Volume 2, 4th Edition. VitalSource Bookshelf 10.1.0.
10. Franco, L., Sánchez, C., Bravo, R., Rodriguez, A., Barriga, C., & Juánez, J. C. (2012). The sedative effects of hops (Humulus lupulus), a component of beer, on the activity/rest rhythm. Acta physiologica Hungarica, 99(2), 133–139. https://doi.org/10.1556/APhysiol.99.2012.2.6
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