Sleep, The Circadian Rhythm, and Hormones
The circadian rhythm and sleep are regulated and affected by hormones. Hormones are cyclical and are produced and secreted according to the circadian rhythm. Read on to see how the body’s 24-hour circadian clocks and hormones work together, which affect sleep, obesity and metabolic health.
In this blog, you will learn:
- Which hormones work with the circadian rhythm
- What happens if the circadian rhythm gets misaligned
- How this can impact hormones, sleep, obesity and metabolic health
HORMONES & CIRCADIAN RHYTHM
The circadian rhythm controls various hormones. Hormones also signal and regulate the circadian rhythm.
These hormones include:
- Melatonin
- Insulin
- Ghrelin and leptin
- Cortisol
Melatonin
Melatonin is the sleep hormone that regulates and synchronizes circadian rhythm and the sleep wake cycle. It promotes sleep, reduces sleep latency and increases total sleep time. Melatonin secretion occurs in response to darkness in the evening, which is the body’s signal to go to sleep at night time. Melatonin then rises during the night when it can be 30 times higher than daytime levels (Montaruli, 2021). It then decreases so that we can wake up in the morning. Read more about melatonin in our first blog on sleep here.
Insulin
As melatonin rises in the evening, the body releases less insulin. Insulin is an important hormone that helps get glucose into the cells for energy and manages blood sugar. When we eat, blood sugar, or glucose, goes up and insulin manages and regulates blood sugar. If insulin secretion is reduced due to melatonin secretion, then the ability to digest glucose is inhibited. So, eating a meal too closely to the time of melatonin release, late in the evening, means glucose won’t be handled properly and digestion may be off (Manoogian E, 2019).
Insulin secretion and sensitivity is stronger and better for digestion in the morning. Larger meals are processed better when eaten in the first half of the day.
Insulin and sleep are closely linked. Just one night of poor sleep can dysregulate insulin and increase insulin resistance. This increases sugar and food cravings the next day. After a poor night’s sleep, it is important to eat healthily and try to avoid the temptation to eat too much sugar.
Sleep fragmentation, insulin and glucose
In research, sleep fragmentation for 3 nights in a row led to a 25% decrease in insulin sensitivity and a 23% decrease in glucose tolerance (Reutrakul S, 2018). Over time, the reduced insulin sensitivity can increase hunger, leading to consuming more calories and weight gain.
Insufficient sleep is a risk factor for lower insulin sensitivity, insulin resistance, obesity, type 2 diabetes and other metabolic problems (Reutrakul S, 2018).
Hunger Hormones
Sleep and circadian rhythms influence the appetite hormones ghrelin and leptin. These hormones manage feelings of fullness, hunger, satiety, blood sugar regulation and fat storage.
Ghrelin is the hunger hormone which regulates appetite. The stomach releases ghrelin when it’s empty to signal to the brain that it’s time to eat. Ghrelin is called the hunger hormone. It has a 24-h circadian rhythm that increases over the course of the day and decreases during the night. It increases between meals and decreases after meals.
Ghrelin regulates food intake, body weight, blood sugar, food anticipatory activity and body temperature in a circadian pattern (Kulkarni SS, 2023). It also signals the pituitary gland to release growth hormones and has a role in insulin release.
Leptin is the satiety hormone. It regulates hunger by increasing the feeling of satiety or fullness. It decreases appetite and helps prevent hunger. This regulates energy balance so that the body doesn’t trigger a hunger response when it doesn’t need energy (calories). Leptin mainly acts on the brain and hypothalamus to regulate hunger and energy balance. Leptin also regulates fat tissue and energy storage. Over a 24-h period, leptin is lower during the day and higher at night (Chaput JP, 2022).
Insufficient sleep and hunger hormones
Not sleeping long enough can increase calories burned, due to being awake for a longer time. But if sleep is restricted and food is freely available, people eat far more calories than they burned during the extra time awake. This happens despite changes in appetite hormones that should promote satiety (Chaput JP, 2022).
In sleep-deprived lean adults and overweight/obese adults, the average increase in energy intake is 253 and 385 calories per day respectively (Chaput JP, 2022). The extra 24-h energy intake occurs despite the reduced ghrelin and increased leptin that should reduce hunger (Chaput JP, 2022). The extra calories are mainly eaten as after-dinner snacks and can cause weight gain if maintained over time (Chaput JP, 2022).
Poor sleep disturbs the ghrelin-leptin interaction and can lead to insulin resistance and weight gain, particularly around the abdomen. Even one night of bad sleep disrupts insulin levels. Why this happens is not yet understood. Other mechanisms in addition to changes in ghrelin and leptin are thought to be involved in the extra energy intake and obesogenic effects of chronic insufficient sleep (Chaput JP, 2022). If you do have a night or a few nights of inadequate sleep, then try to avoid eating more sugar and more calories the next day
Cortisol
Cortisol is the stress hormone which also has a circadian rhythm. It rises in the middle of the night and peaks in the early morning hours to promote waking up (Chaput JP, 2022). It is released in a pulsed manner throughout the 24 h circadian cycle (Kim TW, 2015). It stimulates wakefulness in the morning, promotes alertness throughout the day and slowly declines to help sleep drive and other hormones to rise, and then decreases which promotes falling asleep at night.
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SLEEP, OBESITY & METABOLIC HEALTH
Sleep is so crucial to good health yet insufficient sleep is so common in modern society.
- At least 33% of adults in the US sleep less than the recommended 7 hours per night (Chaput JP, 2022).
- Modern society today is active 24 h a day, 7 days a week, which promotes circadian misalignment. People work night shifts during the biological night, when the circadian clocks want to promote sleep, and sleep during the biological day, when the circadian clocks want to promote activity.
- 24-hour access to electric light can delay the timing of the central circadian clock in the brain, which can cause delayed sleep that doesn’t align with the early start times of school and work.
Metabolic health suffers from insufficient sleep and circadian misalignment. This can cause weight gain, obesity and metabolic problems.
- Too short sleep duration of less than 5-6 h per day is linked to a 38% increase in obesity compared with normal sleep duration in adults (Chaput JP, 2022).
- Type 2 diabetes, cardiovascular disease, hypertension and dyslipidemia are metabolic issues linked to insufficient sleep and/or circadian misalignment (Chaput JP, 2022).
Poor sleep, in either amount or timing, is associated with difficulty controlling appetite and can result in obesity. Being overweight or obese increases the risk of developing sleep disorders such as obstructive sleep apnea, which may further impair sleep quality (Lee JH, 2022).
- Insufficient sleep and circadian misalignment are metabolic stressors linked to weight gain and obesity.
- Insufficient sleep increases energy expenditure by ~100 kcal per day but also increases energy intake by >250 kcal per day, resulting in weight gain (Lee JH, 2022).
- Sleep restriction increases the drive to eat. This excess food intake from not sleeping enough is more related to cognitive control, will power and reward mechanisms than to appetite hormones.
- Circadian misalignment reduces 24-h energy expenditure by ~3% (~55 kcal per day), dysregulates appetite hormones and makes it easier to choose unhealthy foods (Chaput JP, 2022).
Sleep duration is associated to BMI
- In one study, people with the highest BMI (body mass index) slept less than 6 hours a day, which is not enough (Larsen SC, 2020).
- The lowest BMI was seen in people sleeping 8–9 h a day (Larsen SC, 2020).
- Similar results were found between sleep time and FMI (fat mass index) (Larsen SC, 2020).
Irregular sleep patterns lead to metabolic issues. Irregular sleep is defined as sleep duration that changes by 1 hour or more between nights.
- Insufficient sleep and changing the sleep pattern increases risk of diabetes (Kianersi S, 2024).
- People with irregular or inconsistent sleep patterns have a higher risk of developing type 2 diabetes (Kianersi S, 2024).
- People with this 1 hour or more change in sleep duration are 34% more likely to develop type 2 diabetes compared to people whose nightly sleep varies less (Kianersi S, 2024).
- The link between fluctuating sleep duration and higher diabetes risk is due to circadian disruption and disturbed sleep (Kianersi S, 2024).
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If you aren’t getting quality sleep and suspect your circadian rhythm or hormones may be misaligned, then get in touch with us at the Medicine with Heart clinic. We can help to dial in your diet, circadian rhythm and get your sleep on track!
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SUMMARY
- Hormones regulate the circadian rhythm and these circadian clocks and hormones work together, to affect sleep, obesity and metabolic health.
- Melatonin is the sleep hormone that regulates circadian rhythm and the sleep wake cycle. It promotes sleep and increases total sleep time.
- Insulin helps manage blood sugar. It has its own circadian rhythm and works in contrast to melatonin. Poor sleep and sleep fragmentation decreases insulin sensitivity.
- Sleep and circadian rhythms influence the appetite hormones ghrelin and leptin. These hormones manage feelings of fullness, hunger, satiety, blood sugar regulation and fat storage.
- Metabolic health suffers from insufficient sleep and circadian misalignment. This can cause weight gain, obesity and metabolic problems.
- Sleep restriction increases the drive to eat. Sleep duration is associated to BMI. Less sleep leads to a higher BMI.
- Irregular sleep patterns lead to metabolic issues. People with irregular or inconsistent sleep patterns have a higher risk of developing type 2 diabetes.
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