Sahha Research

How circadian rhythms and sleep work in Sahha

Sahha's Sleep Score, a concise measure, assesses users' sleep quality and quantity. It amalgamates multiple sleep details to derive impactful insights on rest patterns and their health implications. Here's how we think about circadian rhythms and scoring sleep in Sahha

What is a circadian rhythm?

The circadian rhythm is the human body’s natural 24-hour cycle that regulates various physiological processes, including sleep-wake patterns, hormone release, appetite, digestion, and body temperature (1). It acts as a biological clock that optimizes the timing of these processes, continuously influenced by external factors like light exposure, temperature, and social interactions (2).


The human circadian system is refers to how the human body is influenced by light stimuli and how the circadian rhythms present in humans (3). Therefore the circadian rhythm in the human body can be considered a pattern of cycles and the features of those cycles, such as phases, disruption and alignment (or misalignment)(4). For example, a circadian phase considers the patterns in rest vs activity that a human engages in within a 24 hour period.


There are several formulas (i.e. mathematical equations) that are used to calculate the human circadian system. These formulas usually consider features called “circadian variables” such as the time of day, sleep midpoint, and dim light melatonin onset (5). When these variables are collected from wearables, they result in what’s known as “proxy parameters” of circadian information. You can find more detail about circadian rhythms elsewhere, but the main thing to know is why circadian rhythms play a key role in sleep quality.


Put simply, the human body is designed to be awake during daylight (i.e. when the sun is up), and asleep when it is dark. This is due to our bodies producing a hormone called melatonin. Melatonin is produced by the pineal gland in the brain. It plays a crucial role in regulating the sleep-wake cycle and is often referred to as the “hormone of darkness” because its production is triggered by darkness. Melatonin helps signal the body to prepare for sleep and is involved in the synchronisation of the circadian rhythms to one’s environmental light-dark cycle. So, you can see that if the time you sleep and wake are not aligned with the light and dark cycles in your environment, your body will be misaligned and you’ll generally feel a little lousy. This is the key reason why capturing circadian rhythm information can help improve your sleep quality and your overall health.

How did we create the Sahha Sleep Score?

The score takes into account the following aspects of sleep: total sleep time, night time activity, sleep regularity, sleep routine and sleep debt. These aspects of sleep are called “factors” (a term we gave them) which each have their own formulas. You can find out more about the formulas behind each of these factors on our website here (link website).


Once we have the factors, we give each one a weighting depending on how important they are to determining the overall quality of one’s sleep. The way we determine the weighting is based on the existing research about each aspect of sleep. You can find out more about what the research say about these aspects of sleep here (link to website).


We then combine all the factors to produce one “score” which ranges from 0-1, where 0 is considered “minimal” and 1 is considered “high”

  • NOTE: we need to link each state (minimal, low, medium, high) to a specific numeric value - waiting on this info


But we haven’t stopped at your average sleep score data (see common sleep scores here - link to previous article). At Sahha we are at the forefront of sleep score creation which is why we have included the concept of “circadian rhythm” in our sleep score factors.

  1. Stewart, A. J., & Plotkin, J. B. (2020). From extortion to generosity, evolution in the iterated prisoner’s dilemma. Interface Focus, 10(3), 20190098. https://doi.org/10.1098/rsfs.2019.0098

  2. https://nigms.nih.gov/education/fact-sheets/Pages/Circadian-Rhythms.aspx

  3. Kronauer RE, Forger DB, Jewett ME. Quantifying human circadian pacemaker response to brief, extended, and repeated light stimuli over the phototopic range. J Biol Rhythms. 1999;14(6):500–515. doi:10.1177/074873099129001073

  4. Massimiliano de Zambotti, Cathy Goldstein, Jesse Cook, Luca Menghini, Marco Altini, Philip Cheng, Rebecca Robillard, State of the science and recommendations for using wearable technology in sleep and circadian research, Sleep, Volume 47, Issue 4, April 2024, zsad325, https://doi.org/10.1093/sleep/zsad325

  5. Cheng P, Walch O, Huang Y, et al.  Predicting circadian misalignment with wearable technology: validation of wrist-worn actigraphy and photometry in night shift workers. Sleep. 2021;44(2). doi:10.1093/sleep/zsaa180

Sahha Research

How circadian rhythms and sleep work in Sahha

Sahha's Sleep Score, a concise measure, assesses users' sleep quality and quantity. It amalgamates multiple sleep details to derive impactful insights on rest patterns and their health implications. Here's how we think about circadian rhythms and scoring sleep in Sahha

What is a circadian rhythm?

The circadian rhythm is the human body’s natural 24-hour cycle that regulates various physiological processes, including sleep-wake patterns, hormone release, appetite, digestion, and body temperature (1). It acts as a biological clock that optimizes the timing of these processes, continuously influenced by external factors like light exposure, temperature, and social interactions (2).


The human circadian system is refers to how the human body is influenced by light stimuli and how the circadian rhythms present in humans (3). Therefore the circadian rhythm in the human body can be considered a pattern of cycles and the features of those cycles, such as phases, disruption and alignment (or misalignment)(4). For example, a circadian phase considers the patterns in rest vs activity that a human engages in within a 24 hour period.


There are several formulas (i.e. mathematical equations) that are used to calculate the human circadian system. These formulas usually consider features called “circadian variables” such as the time of day, sleep midpoint, and dim light melatonin onset (5). When these variables are collected from wearables, they result in what’s known as “proxy parameters” of circadian information. You can find more detail about circadian rhythms elsewhere, but the main thing to know is why circadian rhythms play a key role in sleep quality.


Put simply, the human body is designed to be awake during daylight (i.e. when the sun is up), and asleep when it is dark. This is due to our bodies producing a hormone called melatonin. Melatonin is produced by the pineal gland in the brain. It plays a crucial role in regulating the sleep-wake cycle and is often referred to as the “hormone of darkness” because its production is triggered by darkness. Melatonin helps signal the body to prepare for sleep and is involved in the synchronisation of the circadian rhythms to one’s environmental light-dark cycle. So, you can see that if the time you sleep and wake are not aligned with the light and dark cycles in your environment, your body will be misaligned and you’ll generally feel a little lousy. This is the key reason why capturing circadian rhythm information can help improve your sleep quality and your overall health.

How did we create the Sahha Sleep Score?

The score takes into account the following aspects of sleep: total sleep time, night time activity, sleep regularity, sleep routine and sleep debt. These aspects of sleep are called “factors” (a term we gave them) which each have their own formulas. You can find out more about the formulas behind each of these factors on our website here (link website).


Once we have the factors, we give each one a weighting depending on how important they are to determining the overall quality of one’s sleep. The way we determine the weighting is based on the existing research about each aspect of sleep. You can find out more about what the research say about these aspects of sleep here (link to website).


We then combine all the factors to produce one “score” which ranges from 0-1, where 0 is considered “minimal” and 1 is considered “high”

  • NOTE: we need to link each state (minimal, low, medium, high) to a specific numeric value - waiting on this info


But we haven’t stopped at your average sleep score data (see common sleep scores here - link to previous article). At Sahha we are at the forefront of sleep score creation which is why we have included the concept of “circadian rhythm” in our sleep score factors.

  1. Stewart, A. J., & Plotkin, J. B. (2020). From extortion to generosity, evolution in the iterated prisoner’s dilemma. Interface Focus, 10(3), 20190098. https://doi.org/10.1098/rsfs.2019.0098

  2. https://nigms.nih.gov/education/fact-sheets/Pages/Circadian-Rhythms.aspx

  3. Kronauer RE, Forger DB, Jewett ME. Quantifying human circadian pacemaker response to brief, extended, and repeated light stimuli over the phototopic range. J Biol Rhythms. 1999;14(6):500–515. doi:10.1177/074873099129001073

  4. Massimiliano de Zambotti, Cathy Goldstein, Jesse Cook, Luca Menghini, Marco Altini, Philip Cheng, Rebecca Robillard, State of the science and recommendations for using wearable technology in sleep and circadian research, Sleep, Volume 47, Issue 4, April 2024, zsad325, https://doi.org/10.1093/sleep/zsad325

  5. Cheng P, Walch O, Huang Y, et al.  Predicting circadian misalignment with wearable technology: validation of wrist-worn actigraphy and photometry in night shift workers. Sleep. 2021;44(2). doi:10.1093/sleep/zsaa180