Chronotype is influenced by differences in circadian rhythm, which refers to the fundamental 24-hour physiological cycle essential for various molecular and behavioral processes. It helps regulate sleep patterns.
The timing of circadian rhythms varies across individuals and is influenced by both environmental and genetic factors. People with earlier rhythms tend to rise early in the morning and feel sleepy earlier in the night. If your body sides with the “morning clock” then you are a “morning person.” The other end of this spectrum has people with delayed rhythms. They tend to sleep and wake up late and are often referred to as an “evening person” or a “night owl.”
Research has shown that morning people are more focused, persistent, agreeable, plan their future better, and are less likely to smoke and drink or get depressed. They may exhibit characteristics like:
- Waking up early
- Being more active during the morning hours
- Being more focused and happy
- Being more productive during the day
Similarly, night owls enjoy a burst of strength during the night and may exhibit characteristics like:
- Waking up late
- Being more active during the evening hours
- Being more creative and adventurous
- Being more productive during the night
A GWAS study of self-reported chronotype (morning/evening person) of UK Biobank data identified 22 regions in the circadian rhythm and photo-reception genes associated with morningness. This was also replicated in a 23andMe study.
One of the strongest associations was seen in the rs516134 SNP located near the RGS16 gene.
The RGS16 gene encodes a protein that belongs to the regulator of G protein signaling. This protein is responsible for turning off certain signal communications between cells in the body.
Microarray studies and gene expression analysis have demonstrated that the RGS16 gene exhibits circadian variations. According to a study, mice lacking this gene have a longer circadian period.
The rs516134 is a C>T polymorphism located in the RGS16 gene. The C allele is found to be strongly associated with morningness.
Non-genetic Influences On Circadian Rhythm
A study found that morningness is significantly associated with gender, with a prevalence of 39.7% in males and 48.4% in females.
Also, people over 60 were more likely to prefer mornings than people under 30 - meaning people’s sleep preferences may change over time.
Circadian rhythms affect day-to-day bodily functions such as sleep, eating habits, hormones release, and body temperature.
Many studies have documented that irregular rhythms are linked to various chronic conditions such as sleep disorders, obesity, depression, diabetes, hypertension, bipolar, and schizophrenia.
It is known that the vast majority of patients with depression have sleep abnormalities; either they sleep too much or have insomnia and can’t sleep at all.
Several genetic variants are correlated with how circadian rhythms function and their association with health conditions.
The interplay between genetics and non-genetic factors (such as sunlight, eating habits) with circadian rhythm is clear.
Maintaining a routine with a balanced lifestyle may help to stabilize the internal biological clock and health.
Sleep is a critical component of optimal health. A healthy sleep comprises various aspects, including adequate duration, good quality, and the absence of sleep disorders. Inadequate sleep at night is generally associated with:
- Daytime sleepiness
- Daytime fatigue
- Depressed mood
- Poor functioning
- Other health issues
Sleep duration refers to the total amount of sleep obtained either during the nighttime sleep event or across the 24-hr period.
Importance of An Adequate Sleep
Getting enough sleep at night is very important for several reasons. Sleep is linked to your mental and physical health and quality of life. When you get adequate sleep at night, you can be more productive and concentrate better during the day. It reduces your risk of heart disease and prevents depression. Your immune system becomes stronger as sleep helps the body to repair and recover. Your athletic performance can also be improved because of a good night’s sleep. Not getting enough sleep can make you gain weight faster.
RDA: What Is The “Ideal” Sleep Duration?
National Sleep Foundation guidelines recommend 7-9 hours of sleep per night for healthy adults. Babies, young children, and teens need even more sleep to enable their growth and development. People over 65 should also get 7 to 8 hours of sleep per night.
How Does Genetics Affect Sleep Duration?
Studies have shown that certain genetic variants influence habitual sleep duration, which explains why some individuals need more sleep than others.
Twin studies have shown that the heritability estimation of sleep duration is around 10 - 40%.
A GWAS study of self-reported chronotype and sleep duration of UK Biobank data identified several genetic regions associated with sleep duration. This study documented that people with genetic variants for longer sleep duration reported an average of 22 minutes more sleep.
The PAX8 gene encodes a member of the paired box (PAX) family of transcription factors involved in thyroid follicular cell development and the expression of thyroid-specific genes.
Variations in the PAX8 gene may affect different functions, including DNA binding, gene activation, and protein stability.
Research studies have found that the sleep-wake cycle may be influenced by regulating thyroid hormone levels. Individuals with hypothyroidism (a condition in which the thyroid gland does not produce enough thyroid hormones) are prone to excessive sleepiness. People with hyperthyroidism (in which the thyroid makes too much of the hormone), on the other hand, may have insomnia.
The rs62158211 is a G>T polymorphism located in the PAX8 gene. The T allele is associated with longer sleep duration.
A study documented that the rs62158211 was associated with an average 2.6-minute per-allele change in sleep duration.
Non-genetic Influences On Sleep Duration
Some risk factors that lead to shorter sleep duration include alcohol consumption, smoking, and physical inactivity.
Effects of Sleep Duration on Health
Few epidemiological and genetic studies have demonstrated a strong biological link between abnormal sleep duration, risk of schizophrenia, type 2 diabetes, fetal growth, and Crohn's disease.
Sleep duration is also associated with cardiovascular diseases, type 2 diabetes, depression, automobile and workplace accidents, learning and memory problems, and prospective mortality.
TipsTo Become An Early Riser
Snoring is the loud or harsh sound from the nose or mouth that occurs when breathing is partially obstructed. The sound is produced when the soft palate and other soft tissues (such as uvula, tonsils, nasal turbinates, and others) in the upper airway vibrate.
Affecting nearly 90 million Americans, it can lead to disturbed, unrefreshing sleep, ultimately resulting in poor daytime function. Snoring is caused due to obstruction of air passage, resulting in the vibration of respiratory structures and the production of sound during breathing while asleep.
Snoring is more prevalent in males than in females. Certain risk factors such as genetic predisposition, throat weakness, obesity, mispositioned jaw, obstructive sleep apnea, sleep deprivation, alcohol consumption, and mouth breathing are associated with snoring.
How Does Genetics Influence Snoring Risk?
Twin and family studies have identified the association between genetic factors and snoring risk, with heritability ranging between 18 to 28%.
A recent study published in 2019 leveraged data from a large U.K. Biobank study consisting of the Australian adult population to identify the molecular mechanisms associated with snoring.
MSRB3 is associated with protein and lipid metabolism pathways, which are related to hippocampal volume (a region in the brain) and lung function. Such genetic associations are consistent with the findings that severe bouts of snoring may be due to:
- Nocturnal oxygen desaturation (temporary drop in oxygen levels in hemoglobin)
- Lowered neuropsychological functions, with reduced ability to consolidate memory.
The rs10878269 is G>A polymorphism located in the MSRB3 gene. A study by Jones, Samuel E., et al.2016 showed that variant rs10878269 was significantly associated with reduced snoring risk.
Non-genetic Influences On Snoring
Effects Of Snoring
Snoring is not often considered a serious health concern except in some conditions. Snoring can usually be cured through simple home remedies. Light and infrequent snoring is completely normal. Snoring that is linked to obstructive sleep apnea (OSA) is, however, worrisome and needs to be treated.
Tips For A Snore-free Sleep
Insomnia (also known as sleeplessness) is a common sleep disorder that is characterized by the inability to fall asleep or stay asleep at night, resulting in tired or unrefreshing sleep.
According to the American Psychiatric Association (APA), insomnia is the most common sleeping disorder.
Approximately 30% to 40% of adults in the United States report symptoms of insomnia.
A diagnosis of insomnia needs to meet the following two categories:
- Difficulties in sleep for at least three nights a week for a minimum of three months
- Difficulties in sleep that results in functional distress in the individual’s life
This can be caused by variations in biological, psychological, and social factors, which most often result in a reduced amount of sleep.
How Does Genetics Influence Insomnia Risk?
A research study published in 2019 found an association between certain variants in genes like DLG4, LRRK2, DNM1, CRH, GRIN1, DRD1, DRD2, SNCA, DRD4, NTSR1, CNTN2, and CALB1, and insomnia. DNM1 gene codes for the synaptic neuronal protein dynamin 1, which is associated with pre-sleep arousal, a characteristic feature among people with insomnia.
According to a research study, the heritability of insomnia is between 38 to 59%. This suggests a role of genetic factors in insomnia.
Tissue-specific gene-set analyses showed that insomnia might have higher genetic signals among genes that are usually expressed in the brain. The functions of these regions of the brain are of relevance to insomnia.
The genetic correlations between insomnia and psychiatric traits were stronger than the genetic correlations between insomnia and other sleep-based characteristics. According to the study, this suggests that genetically, insomnia resembles neuropsychiatric traits more closely than other sleep-related characteristics.
The MEIS1 gene is a transcription factor that plays a key role in hematopoiesis, endothelial cell development, and vascular patterning.
It also plays a role in neurodevelopment.
Research studies have shown that the reduced MEIS1 levels and function of the gene may contribute to the pathogenesis of sleep-related disorders.
The rs113851554 is a G>T polymorphism located in the MEIS1 gene, which is found to be correlated with multiple sleep disorders.
A study found that the T allele of rs113851554 is associated with [an increased risk of developing insomnia symptoms] (https://pubmed.ncbi.nlm.nih.gov/27992416/). Also, functional study analysis suggested that the rs113851554 in the MEIS1 locus is most strongly associated with insomnia disorder.
Non-genetic Influences On Insomnia Risk
Insomnia is more common in women than in men. In fact, women are twice as likely to fall asleep than men. One in four women has some insomnia symptoms.
Insomnia is more common in older people more than men and younger ones. As many as 50% of older adults complain about difficulty initiating or maintaining sleep.
Effects Of Insomnia On Health
TipsTo Prevent And Manage Insomnia
Caffeine is a central nervous system stimulant, which is widely used for its psychoactive effects. It is commonly used to alleviate behavioral, cognitive, and emotional deficits caused by sleep deprivation.
Regardless of its beneficial effects, caffeine may have adverse sleep-related consequences that might lead to sleep disruption and insomnia symptoms. This is because caffeine consumption is associated with lower levels of 6-sulfatoxymelatonin. 6-sulfatoxymelatonin is a substance produced during the metabolism of melatonin. It is involved in the regulation of circadian rhythm. Lower levels of 6-sulfatoxymelatonin can result in increased alertness (wakefulness).
CYP1A2 encodes cytochrome P-450 group of enzymes. These enzymes influence the absorption and metabolization of caffeine. Caffeine is absorbed rapidly and completely from the gastrointestinal tract. After absorption, the P-450 enzymes help with the metabolization. Variation in the CYP1A2 activity represents a major source of variability in the pharmacokinetics (drug absorption, distribution, metabolism, and excretion) of caffeine.
While the CYP1A2 gene is responsible for caffeine metabolism, another gene, ADORA2A, influences how your sleep is affected by caffeine intake. This gene encodes the adenosine receptor. When an adenosine molecule binds to this receptor, it inhibits all the processes that are associated with wakefulness. Caffeine acts as an adenosine receptor antagonist - it mimics adenosine and goes and binds to the adenosine receptor. This results in increased levels of free adenosine, leading to a boost in neuronal activity and wakefulness.
The adenosine A2A receptor (ADORA2A receptor) plays a role in the effects of caffeine on arousal. Mice lacking functional A2A receptors do not show increased wakefulness in response to caffeine administration, indicating that the A2A receptor mediates the arousal response.
The rs5751876 is a T>C polymorphism located in the ADORA2A gene, which modulates the sleep-wake cycle, and contributes to individual sensitivity to caffeine effects on sleep.
Studies have documented that in caffeine consumers (less than 300mg), rs5751876 - T allele is associated with a decreased risk of sleep complaints and insomnia as compared to the C allele.
If caffeine consumption is not wisely regulated, it could lead to delayed sleep and sleep deprivation. Sleep deprivation is associated with lapses in attention, lowered alertness, and reduction in cognitive function. Scientific studies have shown that a reduction in sleep time of 90 minutes could reduce objective alertness during the day time by one-third.
Obstructive Sleep Apnea (OSA) is a common, serious, and potentially life-threatening sleep disorder. It is characterized by frequent episodes of partial or complete upper airway obstruction during sleep.
This results in intermittent hypoxemia (low level of oxygen in the blood) and arousal.
Here, the throat muscles relax at irregular intervals and fail to keep the airway open. This results in inadequate breathing for 10 seconds or longer. Thus, the oxygen levels lower, and carbon dioxide levels build up. The brain interprets this as a need to open the airway and wakes you up in the process. This awakening is usually too brief to be remembered. A very noticeable sign of OSA is snoring.
More than 18 million American adults have been estimated to have sleep apnea.
How Does Genetics Influence the Risk of Obstructive Sleep Apnea?
Genes thought to be associated with the development of obstructive sleep apnea are involved in many body processes. They include:
- Communication between nerve cells
- Breathing regulation
- Control of inflammatory responses by the immune system
- Development of tissues in the head and face (craniofacial development)
- The sleep-wake cycle
- Appetite control
African-Americans and Pacific Islanders have more genetic variants associated with sleep apnea than Europeans. Variations in genes such as TNF, CRP, PLEK, PTGER3, LPAR1, HTR2A, and GDNF are associated with the risk of obstructive sleep apnea. Studies suggest that variations in multiple genes, each with a small effect, combine to increase the risk of developing the condition.
The TNFA gene encodes a proinflammatory cytokine (a molecule released by the T-immune cells) that belongs to the tumor necrosis factor (TNF) superfamily. It regulates various biological processes, including cell proliferation, differentiation, apoptosis, lipid metabolism, and coagulation. Studies have shown that TNF is involved in the regulation of sleep by influencing the adenosine receptor expression.
The rs1800629 is G>A polymorphism located in the TNFA gene associated with increased transcriptional activity and higher TNF levels. This SNP has been studied to contribute to the pathogenesis of sleep disorders. Studies have shown that the rs1800629 - A allele carriers are associated with an increased risk of developing obstructive sleep apnea when compared to G allele carriers.
Non-genetic Influences On OSA Risk
Some non-genetic risk factors for OSA are:
- Narrowed airway
According to a 2013 study, people with type 2 diabetes have nearly a 50% chance of being diagnosed with OSA. Both of these often coexist because of shared risk factors.
Effects Of OSA on Health
Some effects of OSA that could interfere with everyday functioning include:
- Difficulty in concentrating
- Excessive daytime sleepiness
- Irritability, sexual dysfunction
- Nighttime sweating
- Learning and memory difficulties
Tips for Managing Obstructive Sleep Apnea
Excessive daytime sleepiness (also known as hypersomnia) refers to the inability to stay awake and alert during the normal waking hours that results in unexpected lapses of sleep or drowsiness. It can even occur after long stretches of sleep.
There are two types of hypersomnia; primary and secondary.
Primary hypersomnia occurs without an underlying medical condition. The only symptom is excessive fatigue.
Secondary hypersomnia, on the other hand, occurs due to a medical condition.
Some symptoms of hypersomnia include:
- Low energy
- Loss of appetite
A 2019 study in Nature Communications documented that nearly 10–20% of people deal with excessive sleepiness to some degree.
How Does Genetics Influence the Risk of Excessive Daytime Sleepiness?
Studies have shown that certain genetic variants influence daytime sleepiness, which explains why some individuals need more sleep than others. Twin study results have estimated a 38% genetic variance in daytime sleepiness.
Studies have found an association between excessive daytime sleepiness and certain variations in the HCRTR2, PATJ, AR-OPHN1, KSR2,, and PDE4D genes.
The HCRTR2 gene encodes a protein that belongs to the G-protein coupled receptor, involved in the regulation of appetite, energy balance, neuroendocrine functions, and wake promotion.
Latest research studies suggest that variations in the HCRTR2 gene may influence the sleep-wake process.
Non-genetic Influence on EDS Risk
The most common causes of excessive sleepiness include:
- Low sleep duration
- Poor quality sleep
- Sleep deprivation
- Obstructive sleep apnea
- Medications with sedative properties
Research has also indicated that other health conditions can increase the risk of excessive sleepiness. Some of them include:
- High BMI (Obesity)
- Type 2 diabetes
Effects Of Excessive Daytime Sleepiness (EDS) on Health
Studies have shown that EDS is associated with an increased risk of developing coronary heart disease and stroke. However, the risk can be managed by improving the quality of sleep.
People with EDS also have poorer health than comparable adults.
According to a study, EDS is associated with negative effects on cognitive function. In fact, EDS is a common symptom in neurological conditions like Parkinson’s and psychiatric conditions like depression.
Tips for Managing Obstructive Sleep Apnea
Narcolepsy is a sleep disorder that is characterized by five symptoms:
1. Excessive daytime sleepiness
2. Cataplexy (sudden muscle weakness that occurs without any 'warning')
3. Sleep paralysis (a state of awareness with an inability to speak or move - usually occurs during waking up or falling asleep)
4. Hypnagogic hallucinations (vivid dreamlike experiences),
5. Disturbed nocturnal sleep
It affects approximately 1 in 2000 individuals and usually appears during childhood or early puberty.
There are two major types of narcolepsy:
Type 1 narcolepsy (NT1) : It is characterized by excessive daytime sleepiness as well as cataplexy. People with NT1 have lower levels of a brain hormone called hypocretin.
Type 2 narcolepsy (NT2) : Nt2 is a type of narcolepsy without cataplexy. People with NT2 have normal levels of hypocretin.
How Does Genetics Influence the Risk Of Narcolepsy?
The heritability among monozygotic twins for NT1 was found to be 20-30%.
If a first-degree family member has NT1, your risk for NT1 increases by 10-40 times. This shows that there are some genetic and environmental factors that play an important role in narcolepsy.
There are multiple genes that are associated with NT1, but almost all patients with NT1 carry a specific variant of the human leukocyte antigen (HLA).
HLA system regulates immune functioning in the body.
The currently identified genetic factors do not fully reveal the heritability of narcolepsy.
However, narcolepsy has been associated with a significant reduction in orexin producing neurons in the brain. Orexin is a neurotransmitter that is considered the master regulator of the sleep-wake cycle. A deficiency of orexin-producing neurons can cause narcolepsy.
The P2RY11 gene is a member of the G-protein coupled receptors family, expressed by the immune cells. It plays an essential role in immune functioning and cell death regulation.
Variations in the P2RY11 gene might dysregulate the functioning of certain immune cells like CD8+T-cells and contribute to the development of narcolepsy.
The rs2305795 is a G>A polymorphism located in the P2RY11 gene on chromosome 19.
A study documented that the rs2305795 A allele is associated with a reduced immune response to infectious triggers, thereby contributing to narcolepsy risk.
Non-genetic Influences On Narcolepsy Risk
Some risk factors for narcolepsy include:
- Autoimmune effects
- Upper airway infection
- Head injury
- Age (10-30 years)
Effects of Narcolepsy on Health
TipsTo Manage Narcolepsy
There is no cure for narcolepsy, but certain lifestyle changes and treatments can help you manage it.
1. Try to stick to a sleep schedule, including short naps for about 20 minutes during the day.
2. Avoid alcohol, nicotine, and caffeine consumption, especially at night, and eat healthily.
3. Include some exercise in your daily routine to make you feel more awake during the day and tired at night.
4. Try to avoid activities that may be dangerous if you fall asleep suddenly, like driving or get enough sleep before you do that activity if necessary.
5. Talk to everyone you work with about your condition. They need to be informed so that they can help you if needed and know how to react.
6. Your doctor may prescribe stimulant medicines to help you stay awake during the day and antidepressants to help with the nightmares and hallucinations.
7. Counseling and support groups can help you relieve your emotions and deal better with the condition.
Sleep efficiency refers to the percentage of time a person sleeps to the amount of time a person spends in bed. It is calculated by the ratio of the total time spent asleep (TST) in a night compared to the total amount of time spent in bed. An efficient sleep leads to a deeper sleep of better quality with lesser disturbances that may result in good stamina and sufficient rest upon waking, while an inefficient sleep may lead to uneasiness and fatigue.
Sleep Efficiency Rates
Sleep efficiency rates tend to vary from person to person. Normal sleep efficiency is considered to be 80% or greater. For example, if an individual spends 8 hours in bed, at least 6.3 hours or more should be spent sleeping to achieve 80% or greater sleep efficiency. Most healthy and young adults have sleep efficiencies above 90%.
How Does Genetics Influence Sleep Efficiency?
UFL1 is one of the genes in the ubiquitin pathway - the principal mechanism behind protein breakdown.
This pathway has also been implicated in schizophrenia, a condition in which poor sleep efficiency is a common symptom.
The relevance of this pathway in sleep disturbances was further explored in another study.
The study indicated that the expression of a protein UFM1, a part of UFL1, increased after partial sleep restriction.
A GWAS analysis found a significant correlation between a variant (rs75842709) near the UFL1 gene and sleep efﬁciency.
The T-allele was associated with a 5.7% decreased sleep efﬁciency.
Non-genetic Influences Of Sleep Efficiency
Some factors that lower sleep efficiency:
- Higher fatigue
- Less activity during the day
- Light at night
- Jet lag
- Sleep environment
Tips To Improve Sleep Efficiency
Sleep latency (also known as sleep onset latency) refers to the amount of time it takes for a person to fall asleep. Usually, normal sleep latency is 5-15 minutes. If sleep latency is less than five minutes, it may suggest some level of excessive sleepiness, and if it is greater than 15 minutes, it may be due to sleep initiation issues.
Sleep latency varies from person to person. An ideal sleep latency period lays the foundation for a solid night's sleep. Sleep latency directly affects sleep efficiency, because if a person is able to fall asleep quickly, they are more likely to have an efficient sleep.
How Does Genetics Influence Sleep Latency?
Research studies have demonstrated the association between certain variants in RBFOX3 and DRD2 genes and sleep latency. The RBFOX3 gene plays a key role in neuron-specific alternative splicing (a process that removes the "unwanted" portions from the DNA and connects useful portions to form a functional gene).
RBFOX3 also influences the release cycle of neurotransmitters, including GABA (gamma-aminobutyric acid) and various monoamines, vital to the human circadian clock.
The DRD2 gene encodes a dopamine receptor. Dopamine is a 'happy hormone' that is crucial for signaling pleasure and reward. Dopamine and its receptors also play a part in controlling the sleep-wake cycle. Mainly, dopamine can help keep you awake and alert. The DRD2 gene variations may affect this wake/sleep switch, leading to a tendency for shorter sleep duration and sleep onset latency.
The rs17601612 is a G>C polymorphism located in the DRD2 gene, which might affect the wake/sleep cycle. A study, Cade, Brian E., et al.2016, has shown that the rs17601612 C allele was strongly associated with shorter sleep latency than the G allele.
Non-genetic Influences on Sleep Latency
A variety of other factors influence sleep latency. They include:
- Dietary intake
- Sedentary life
- Consumption of stimulants
- Illness such as depression
Effects of Delayed Sleep Latency on Health?
Prolonged sleep latency may shorten sleep duration and lead to a variety of problems, including depression, loss of productivity, irritability, cognitive impairment, poor academic performance in children, and adolescents. Persistently increased sleep latency is also a key indicator of delayed sleep phase syndrome, insomnia, sleep deprivation, and narcolepsy.
Tips To Improve Sleep Efficiency