Optimal sleep is complex and poorly understood. Optimal sleep can be defined as “the daily amount of sleep that allows a subject to be fully awake (i.e. not sleepy) and able to sustain normal levels of performance during the daytime” as well as “the amount of sleep required to feel refreshed in the morning”. However, such definitions have been contested with arguments that there is “no magic number” for optimal sleep. Despite uncertainties surrounding definitions of optimal sleep, sleep duration has traditionally been used as a marker of adequate sleep, with the presence of sleep duration recommendations reinforcing this notion. Sleep recommendations however, acknowledge the complexity of optimal sleep and sleep need may be influenced by inter and intra-individual factors. For example, health authorities recognize that everyone may have different sleep requirements and other characteristics of sleep, such as sleep quality, timing, composition, day-to-day variability, and continuity also play an important role. Likewise, it is also recognized that behavioral adaptations and environmental context may also alter sleep requirements. Although efforts have been made to inform current sleep recommendations, much more work is needed in this area, particularly in order to appropriately inform public policies.1 This article mainly focuses on the importance of sleep duration, the recommended sleep duration for different age groups, variations with different professions, factors affecting the duration of sleep and its health outcomes with some tips to improve the quantity of sleep.
Importance of sleep duration
Sleep is an important fundamental biological mechanism for the physical, mental and social well-being of both children and adults. With the growing research, duration of sleep has received a lot of attention and proved to have major influence on various biological processes such as inflammation, glucose regulation, appetite, energy expenditure as well as psychological mechanisms like memory consolidation, learning and attention. Given the importance of sleep duration, concerns have risen with the continual advances in technologies such as artificial lighting, television, laptops, tablets, smartphones, internet and other screen-based devices are believed to be one of the reasons for shorter sleep at night. It is widely accepted that sleep is decreasing as the society modernizes. The seemingly decline in sleep has raised multiple health concerns. Considering the importance of sleep for physical and mental tasks, feelings of inadequate or poor sleep may reflect the need for more sleep in order to deal with increased cognitive demands of modern life.1
Sleep recommendations for different age groups:
The mission of National Sleep foundation (NSF) is to improve the health and well-being through proper sleep education and recommendations. The goal of this foundation is to provide most up-to-date scientifically proven sleep health recommendations. Following are the healthy sleep recommendations for different age groups:2
Newborns (0-3 months): Newborns spend most of their time sleeping and it is important for the development of brain and body. The appropriate sleep duration in newborns influences cognitive, physical, developmental and emotional health. The circadian rhythm of newborns is totally different from that of young adults or adults. The circadian rhythm is not fully developed in newborns, therefore sleep can happen at any time of the day. According to guidelines, the normal recommended sleep for newborns is approximately 14 to 17 hours per day. The periods of wakefulness and sleep are irregular with an average continuous period of 2.5 to 4 hours. The sleep in newborns is of three types: quiet sleep, which is similar to NREM in adults, active sleep (equivalent to REM) and intermediate sleep. Muscle movements and rhythmic breathing cycles mark quiet sleep. On the other hand, active sleep comprises of sucking motion, twitches, smiles, frowns, irregular breathing and gross limb movements. The sleep cycles in newborns are less efficient as compared to adults, resulting in easily interrupted sleep.2,3
Infants (4-11 months): The circadian rhythm begins to develop into more mature patterns between 4-11 months of age. The response to dark and light phases increases with better synchronization of wake-sleep cycle of infants. The timing and duration of sleep inclines more towards the night time hours. As the infant grows, the night time cycles increase to 6-hour long continuous sleep episodes constituting a total recommended sleep of 12-15 hours.2,3
Toddlers (1-2 years) and Preschoolers (3-5 years): As the child grows, the sleep needs changes drastically. The recommended sleep decreases to 11-14 by the age of 2, then to 12 by the age of 3 to 4 years and further reduces to 10 by the age of 5 years. The sleep duration of child not only depends on the age but also on the environment and the family schedule. Most amount of the sleep in toddlers and pre-schoolers is mostly concentrated on the night time sleep constituting to be 10-12 hours on an average.2,3
School-age (6-13 years): Nine to eleven hours of sleep is recommended per day for school aged children. Research has proved the association of short sleep durations in school going kids and lower cognitive functioning and poorer academic performance. In addition to age another factor that plays an important role in recommending sleep in ages of 12 to 13 years is the pubertal maturation. A post-pubertal adolescent typically sleeps less due to hormonal changes as compared to a prepubertal school aged kid.3
Teenagers (14-17 years): For overall health and well-being, an eight to ten hours of sleep is recommended for teenagers. Sleep in teenagers is mostly affected by the increased screen-time, delayed sleep timings and early school-start times. The short sleep durations in teenagers is associated with decreased alertness, obesity, poor hearth, increased risk of accidents, depressed moods and low academic performance.3
Young adults (18-25 years): A sleep duration of 7 to 9 hours is recommended for young adults considering the overall health, well being as well as cognitive, emotional and physical health. Sleep in young adults who just started working varies significantly from the college students. Sleep in young adults is highly affected by the school, work and social responsibilities. Insufficient sleep in young adults is commonly associated with poor physical, psychological performance and increased fatigue and mood alterations.3
Adults (26-64 years): The recommended sleep for adults is 7 to 9 hours per day. Sleep deprivation is a common problem is adults with increased responsibilities of work, home, kids. Insufficient sleep in adults generally leads to adverse effects on multitasking, weight regulation, blood pressure, heart problems, overall health disturbing the balance of work and home.3
Older adults (≥ 65 years): Several studies have reported changes in sleep with ageing. There is a decrease in REM sleep and a compensatory increase in lighter stages of sleep. The total sleep time and sleep efficiency reduces with age with increase in number of sleep stage shifts. The recommended sleep in old age is 7 to 8 hours. With all the changes in neural and physical pathways, it can lead to excessive day time sleepiness, which further changes to habitual or intentional napping.4
Effects of different professions on sleep duration
In the modern busy world, employment, odd working hours, night shifts, hectic schedules are considered as of the main reasons for decreased sleep duration and quality. Studies have reported that those who are employed, have multiple jobs and work for long hours. Jobs require lengthy commutes, and certain occupations such as managers, transport/ warehouse workers, and those in manufacturing are at higher risk of inadequate and short sleep. Health care professionals, hospital staff hospital, home nurses and care takers are also at risk for deprived sleep because of the multiple long shifts, taking care of the sick, old or disabled.1 Similarly, Pilcher JJ, et al. (2000) observed shorter sleep durations in permanent night shift workers, as compared to day shifters. Rotating shift work has also been associated with the different types of effects on sleep duration.5 Sleep is presented as an essential and most efficacious component for recovery in training athletes. Studies have reported a substantially poor quality and quantity of sleep.6 In a study on recovery modalities for athletes, sleep deprivation was indicated by either delay in sleep onset (41%) or by difficulties in waking up in the morning (60%).7 Another study by Erlacher D et al. (2011) also reported sleep deprivation and night time waking in athletes.8 The data from literature indicated that athletes may require an increased amount of sleep as compared to the general recommendations for their age groups, suggesting 7-9 hours of night time sleep for appropriate physical and psychological recovery.6
Factors affecting the duration of sleep
Environmental factors: A comfortable and peaceful environment sends a strong signal to brain to rest. The quality and quantity of sleep is highly influenced by the ambience of the room.
Temperature: Temperature of the room or the thermal changes play an important role in initiating the sleep and maintaining a good quality optimal sleep. The circadian rhythm is closely related to the core body temperature and alteration in room temperature to a range of 18° to 26 °C that influences the body temperature to lower down and induce sleep.9
Exposure of light: Day time light exposure influences the production of melatonin, the sleep inducing hormone and helps to maintain the biological clock regulating the cycles of sleep and wakefulness. On the other hand, exposure to night time artificial night or blue led light from various devices has markedly significant side effects on the circadian rhythm and the adequate quality sleep. It increases the sleep onset which could lead to sleep deprivation and adverse effects on the cognitive and physical performance.10
Noise: Noise is a key factor which influences the onset, duration and quality of sleep. A proper room acoustics with no adverse noise from traffic or outside can highly influence the microstructure of sleep. Noise reductions to minimum or a meditating or soul full music can help in early onset of sleep.11
The sleep system: Last but not the least, the sleep system which is formed by the mattress, bed, the pillows and the bedcover highly influences the quality and quantity of sleep. Sleeping on an extra firm or extra soft mattress could lead to an uncomfortable and interrupted sleep and the muscle soreness next morning. Similarly, a proper pillow support around the neck helps in obtaining an optimal quality sleep.12
Health and behavioral factors
Meal composition and timings: Having high carb meals just before bedtime could interfere with the structure of sleep. Heavy meals just before bed can be a cause for indigestion, acid reflux and interrupted sleep at night. On the other hand, it is not advisable to sleep empty stomach also. It could lead to an unsatisfactory and disturbed sleep.13
Exercise: Regular and moderate exercise helps to improve the sleep at night. Exercise or any physical activity increases the release of anabolic hormones in body, elevates core temperature of body and fastens the metabolism. Exercise during day time helps in getting a better sleep at night but exercise close to bedtime could interfere with the pattern of sleep.14
Screen time: With the advancing technology, the use of light emitting devices such as mobiles, laptops, tv for reading, communication and entertainment has increased significantly. More use of these devices cause increase in the exposure to artificial light and delay in onset of sleep leading to insufficient low-quality sleep. It delays the production of melatonin, reduces the amount of sleep and impairs the cognitive and physical activities the next day.15
Habits: There are some behavioral elements which interfere with the sleeping patterns such as consumption of stimulants like caffeine near to bed time. In low to moderate doses alcohol facilitates sleep but chronic consumption can significantly alter the sleep architecture leading to sleep disorders.16
Health issues: Several health problems can interfere with the quality and quantity of sleep. Presence of chronic nagging pain, insomnia, breathing difficulties while sleeping or use of medication for other health disorders can lead to disturbed and poor-quality sleep at night. It is important to deal with the underlying problems for better sleep and health outcomes.
Effects of sleep deprivation on human health
On sleep architecture: Several studies have reported many adverse effects of inadequate sleep or restricted sleep on physical, biological, mental and behavioral aspects of human health. The sleep architecture is affected by the timing and duration of the sleep due to its effect on the rapid eye movement (REM) and Non-Rapid eye movement (NREM) sleep. An increase in slow waves have been observed after a period of sleep restriction, which further lead to a negative correlation between the sleep at night time and the sleep latency (the time of transition from full wakefulness to light sleep stage of NREM) on the following day.16
On neurobehavioral aspects: Inadequate sleep duration can have deleterious effects on the behavioural aspects of a healthy individual which includes impaired attention i.e. reduced vigilance and increased reaction time, increase in information processing in brain, impaired memory and management of dynamic equilibrium during multitasking.16
Physiological effects: There is an increasing evidence of associations between the sleep duration and health outcomes. Sleep loss has been identified as an important factor for detrimental effects of on metabolic, immune, inflammatory and hormonal function.16
Effects on heart and blood pressure: With the increased screen time at night, watching tv, using smartphones or laptops for longer duration has led to the decrease in duration of sleep. Decreased hours of sleep have been reported to cause increased blood pressure in healthy individuals. Individuals with high blood pressure are at increased risk for the development of heart diseases. In otherwise healthy individuals, increased (more than 8 hours) and decreased (less than 7 hours) sleep duration have been associated with increased rates of mortality and coronary artery disease.17
Metabolic disorders: The possible mechanisms that link short sleep duration to hypertension and heart diseases include the increase in weight and changes in the metabolism of glucose and insulin. Observational data from sleep studies have demonstrated significant relation between sleep duration and levels of ghrelin and leptin, which regulate the satiety and hunger. Increased sleep deprivation and its relation to hormonal and metabolic changes causing increase in appetite has led to the increased risk of adverse health outcomes such as obesity, metabolic disorders and heart diseases.18
Weight gain: Over the years, the prevalence of weight gain and its health outcomes has grown to higher proportions. Short sleep duration has proven to be a high-risk factor for weight gain and obesity. The postulated mechanism is that chronic sleep insufficiency causes fatigue in otherwise healthy individuals which could lead to reduced physical activity and resultant weight gain. As discussed above, loss of sleep can have neuro-hormonal imbalances which can lead to increase in calorie intake and weight gain.19
Immunity and inflammation: Inadequate sleep promotes low levels of inflammation, elevates proinflammatory cytokine levels and interleukins (IL-6). Well, the long-term effects of sleep deprivation on inflammatory response are still unclear but one week of modest sleep restriction has been linked with increased production of inflammatory cells in blood. Chronic increase in such levels can have significant adverse effects on health.20
Diabetes type 2: With the rising cases of diabetes mellitus around the world, research is diverting towards exploring the new risk factors. Besides diet, obesity, activity levels, the sleep inducing melatonin hormone also plays a vital role in maintaining circadian rhythm and glucose-insulin function in pancreas. Several studies have reported effects of shorter and longer durations of sleep as risk factors for the chances of diabetes mellitus. In a multiethnic cohort study, short and long duration of sleep increases the risk of cardiovascular mortality by 15-25%.21
Tips for improving sleep
Good sleep habits can sometimes help in obtaining a good quantity and quality sleep. Following are few tips to improve the sleep:
- Be consistent in your schedule. Sleeping and waking up around the same time everyday can help in improving the sleep.
- Make the environment in your sleeping area comfortable with proper temperature settings, noise reduced to minimum and with comfortable mattress, pillows and bedcovers.
- Limit the screen time to at least 30 minutes before the bedtime. It will help in facilitating the sleep onset and better quality of sleep.
- Avoid taking large or heavy meals just before bedtime
- Fix your exercise schedule either in the morning or early in the evening. Avoid doing heavy workouts near to bedtime.
Q1. Is 5 hours of sleep enough?
A1. The ideal time for sleep varies with age but for a healthy adult, sleeping for 5 hours is not enough specially in long term. An adult should at least complete 7 to 8 hours of night time sleep.
Q2. How many hours of sleep a person need?
A2. The need for sleep varies with age. According to guidelines, a healthy adult need a sleep of 7-9 hours, not less than 6 also not more than 11 hours.
Q3. How much sleep do you need by age?
A3. The need for sleep changes with advancing age. According to guidelines, the recommended sleep for different age groups is as follows:
Newborns (0-3 months) – 14 to 17 hours
Infants (4-11 months) – 12-15 hours
Toddlers (1-2 year) – 11 to 14 hours
Preschoolers (3-5 years) – 10-13 hours
School- aged children (6-13 years) – 9 to 11 hours
Teenagers (14-17 years) – 8 to 10 hours
Young adults (18-25 years) – 7 to 9 hours
Adults (2-64 years) – 7 to 9 hours
Older adults (≥ 65 years) – 7 to 8 hours
Q4. How can I wake up at 5am?
A4. The best way to wake up at 5 am is to train your body by following a consistent sleep-wake cycle. This will entrain the body to follow the circadian rhythm and one can wake up at 5 am without an alarm.
Q5. What is the healthy time to wake up?
A5. Ideally waking at early mornings is considered as the healthiest time. Because you are in your lightest REM sleep cycle and mind is slightly awake. as following the guidelines of recommended sleep, one should calculate their waking time completing 7-8 hours of sleep.
Q6. How much sleep is too much?
A6. According to sleep guidelines, for healthy adults sleeping for more than 10 hours is not considered as healthy.
Q7. Do we need less sleep as we age?
A7. As we age, due to the changes in functioning of the body, the production of melatonin decreases, which is the sleep inducing hormone. This could lead to increased sensitivity to surroundings and difficulty in falling asleep. It is a myth to say that with age the need for sleep decreases, according to guidelines individuals above 65 years should sleep for at least 7 to 8 hours.
Q8. Is it healthy to wake up at 5 am?
A8. Several studies have reported that waking early helps to improve the quality of sleep and overall health. It has been reported that individuals sleeping late at night are more likely to develop sleep disorders.
Q9. Is it better to wake up naturally?
A9. It is considered as best to wake up naturally because it means you are done sleeping. On the other hand if u wake up after few hours of sleep it is better to go back to sleep to complete the recommended hours of sleep.
Optimal sleep is essential for normal growth and development, emotional health and immune function. Sleep is a reversible state of mind which is influenced by behavioral and environmental factors. The duration of sleep at night is an important marker for cognitive, physical, emotional and overall health of the individual. To conclude, insufficient or restricted sleep at night could be a high risk factor for several health problems and disturbed state of mind.
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- Pilcher JJ, Lambert BJ, Huffcutt AI. Differential effects of permanent and rotating shifts on self-report sleep length: a meta-analytic review. 2000 Mar 15;23(2):155-63. https://pubmed.ncbi.nlm.nih.gov/10737332/
- Bird SP. Sleep, recovery, and athletic performance: a brief review and Strength Cond J 2013: 35: 43–47. https://insights.ovid.com/strength-conditioning/scjr/2013/10/000/sleep-recovery-athletic-performance-brief-review/8/00126548
- Venter RE. Perceptions of team athletes on the importance of recovery modalities. Eur J Sport Sci. 2014;14 Suppl 1:S69-76. doi: 10.1080/17461391.2011.643924.
- Erlacher D, Ehrlenspiel F, Adegbesan OA, and Galal El-Din H. Sleep habits in German athletes before important competitions or games. J Sports Sci 29: 859–866, 2011.
- Lan L, Tsuzuki K, Liu YF, Lian ZW. Thermal environment and sleep quality: a review. Energy Build. 2017;149: 101– http://dx.doi.org/10.1016/j.enbuild.2017.05.043
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