Scientists from Finland conducted an experiment: four thousand volunteers were monitored for seven years. Specialists recorded the relationship between changes in the work of the organism and the duration of sleep. It turned out that the most resistant to disease men who sleep at least 7 hours 42 minutes/day, and the optimal duration of sleep for women was 7 hours 38 minutes/day. In another experiment, researchers from Arizona (USA) deprived volunteers of access to clocks and light: their body itself had to determine the time of going to bed and the duration of sleep. As a result, the participants went to bed two hours earlier than they were used to in “civilised” life, and the average sleep duration was 7 hours and 20 minutes. Thus, the average recommended sleep duration for an adult is 7-8 hours per night. The amount of sleep needed depends on age. According to generally recognised norms, a one-year-old baby should sleep 12-15 hours, a 10-year-old child – 9-11 hours, a 15-year-old teenager – 8-10 hours. At the same time, modern research shows that there is a genetic predisposition to sleep duration. Scientists from the University of Munich have identified two variants of the ABCC9 gene carrying information about the SUR2 protein, which is responsible for energy processes in cells. The owners of the first variant of the gene needed long sleep much more than the “owners” of the second variant. It also turned out that not only the body’s need for sleep, but also the risk of cardiovascular and metabolic disorders such as diabetes mellitus are associated with the SUR2 protein. According to scientists, this may explain the link between sleep disorders and the development of diseases.

Research conducted in the Edinburgh Sleep Centre with the participation of two thousand British couples has shown how the colour of the walls in the bedroom affects the duration of sleep. It turned out that the longest (7 hours and 52 minutes) sleep people who have decorated their bedroom in blue colours. Yellow (7 hours 40 minutes), green (7 hours 36 minutes), silver (7 hours 33 minutes) and orange (7 hours 28 minutes) colours also have a positive effect on sleep. Those who chose red (6 hours 58 minutes), gold (6 hours 43 minutes), grey (6 hours 12 minutes) and brown (6 hours 5 minutes) wall colours sleep worse. The researchers named lilac as the most inappropriate colour for bedroom walls – it reduces sleep duration to an average of 5 hours and 56 minutes. According to experts, the colour of the walls affects the duration of sleep due to the effect on retinal neurons, and through them – on the brain. In other studies it has been proven that the blue colour does have a positive effect on the nervous system and the body as a whole: it helps to relax, calm down, slow down the heartbeat and reduce blood pressure. Another important aspect is the temperature of the air in the bedroom. According to researchers at the Johns Hopkins University Sleep Centre, the optimal temperature for a good night’s sleep is 18-20 °C.

Sleep experts say that choosing a mattress is very important, as we will spend a third of our lives on it. The degree of mattress hardness/softness in a healthy person depends on individual preferences and does not affect the quality of sleep. If there are any problems, first of all, with the spine, it is better to buy a special orthopaedic mattress. Special orthopaedic pillows can also help with back pain: their choice depends on which part of the spine has problems. It is recommended to change the mattress every 10 years or more often – if you feel that the mattress is “worn out” and does not fulfil its supporting functions. It is recommended to change pillows every two years. Also, according to experts, a good night’s sleep is promoted by clean bed linen. It is important both for the subjective feeling of “freshness” and to reduce the risk of allergic diseases – dander, dust and skin particles quickly accumulate in linen. Therefore, it is recommended to change the linen at least once a week and vacuum the mattress regularly.

Pajamas, nightgowns, underwear – experts believe that any clothing is suitable for sleeping, but it is important that it does not restrict movement and is made of natural fabrics. If you sweat at night, it is better to prefer things made of cotton or linen, if you are cold – from fleece or flannel. Another important rule is that clothes should be intended for sleeping only and should be put on before you go to bed. It should be a kind of ritual that helps your brain to get into the mood for sleep.

Specialists from the University of Surrey (England) believe that it is much more useful to sleep alone. Their research proves that people sleeping together “miss” up to 47 minutes of sleep every night, which is associated with the movements of the partner in sleep, snoring and so on. At the same time, according to other studies, co-sleeping is two per cent more qualitative than sleeping alone – it reduces stress levels, especially in women – but for this to happen there must be a trusting relationship between the partners. According to experts, it is important to organise the right place for co-sleeping. Thus, in some cases it is worth considering buying separate mattresses: for example, if the partners have significantly different body weights, have various health problems, etc., and if they have different health problems. There is no consensus among sleep experts about sleeping together with pets. Among the arguments “against” – the risk of allergic reactions, as well as the increase in body temperature associated with the proximity of the pet, which negatively affects the quality of sleep. At the same time, a number of studies show that despite the fact that people in the company of a four-legged friend can fall asleep longer, sleep efficiency (the ratio of time spent sleeping to time spent in bed) is 81%, while the norm is 80%. It also found that the sleep quality of small dog owners was 0.3% worse than that of a pet weighing more than 50kg.

Does sleep posture matter? Experts from Johns Hopkins University believe that healthy young people can get a good night’s sleep in any body position. At the same time, some postures can aggravate a number of problems. Thus, sleeping on your back is not recommended for neck pain, as well as snoring and a tendency to apnoea (spontaneous stopping of breathing in sleep) – this position contributes to even greater narrowing of the airways. At the same time, sleeping on your back is a way to avoid early wrinkles: when your face comes into contact with the pillow, your face looks “wrinkled” in the morning, and over time the deformation of facial tissues can become permanent. Sleeping on the right side is not recommended for people suffering from gastroesophageal reflux (gastric reflux into the oesophagus) – sleeping on the left side is preferable for them.

People fall into two categories: those who find it easy to fall asleep before midnight and get up at first light, and those whose body resists such a regime in every possible way. What distinguishes the “early birds” from those who love night vigils and late awakenings? Scientists from California conducted a study, which involved more than 89 thousand people. Specialists analysed the data obtained by questionnaires, as well as the results of genetic tests. It turned out that the older people are, the more larks among them: among people under 30 years old only 24% preferred early rising, and among participants over 60 years old – already 63%. It was also found that “owls” among the stronger sex are found 9% more often than among women. The study showed that “larks”, in general, are healthier and happier than “nocturnal predators”. They are 18 per cent less likely to suffer from insomnia, sleep more soundly and often get seven hours of sleep a night. Morning people are also less likely to suffer from depression and weight problems, both overweight and underweight. Another study by Austrian oncologists found that women who prefer to get up early have a lower risk of developing breast cancer. Genetic analysis revealed 15 areas in the genome, in one way or another affecting the time of greatest activity of their carriers. Almost half of the identified areas are related to the regulation of daily biorhythms. Among them were, for example, genes responsible for converting the light signal that arrives in the eyes into an impulse that affects the activity of the brain. Scientists believe that it is the presence of certain combinations of genes that doubles the likelihood that a person will easily get up in the morning hours. However, despite the genetic and biochemical predisposition to a nocturnal lifestyle, experts believe that “owls” have the opportunity to “adjust” their biorhythms: Start getting up an hour earlier than usual, gradually increasing the “shift” to three hours; Stay awake during the daytime hours, and go to bed, respectively, an hour, two or three earlier than usual; Maintain the regime not only on weekdays but also on weekends; For the “transition from owls to larks” is very important dietary regime: breakfast immediately after waking up, lunch at the same time and dinner no later than seven o’clock – a fixed meal will help in the formation of biological rhythms.