Sleep is a cyclical, complex and active vital condition. It consists of several stages having a characteristic pathway due to an interrelation between hormonal and nervous systems. Characterized by reduced consciousness, diminished recognition of environment and reduced movement, sleep is an essential physiological process for survival and proper functioning of the body.

For humans, sleep is the longest activity performed throughout life with an average duration of 8 hours usually distributed in a single night episode, which generally represents about a third of life span. Sleep is an essential physiological process for the renewal of mental and physical functions. Scientifics studies have demonstrated the importance of sleep on vital functions, such as: memory, cognitive development, metabolism, immune system and many others.

Sleep is a process consisting of several phases which are determined through the use of instruments capable of recording the behavior and changes of physiological parameters. A complete sleep cycle takes an average of about 90 minutes and can be repeated 4-6 times during the night. Each cycle consists of phases that are presented in two groups called:

  1. No REM: Are the phases of relaxation and rest during which the body passes from wakefulness to a state of slow activity and deep sleep
  2. REM: Is the phase where it is observed a high brain activity and characterized by rapid eye movements during which the dream function is activated (…is when a person is dreaming) and the physical and vegetative functions are reset, except the motor activity that is inhibited by the cerebral trunk.

    REM: Rapid Eye Movement



Sleep is essential for the survival of the organism. The correct functioning of many organic systems such as immune, metabolic, nervous, cardiovascular and endocrine, are dependent of sleep. Some scientific studies have highlighted the enormous importance of sleep in the regeneration process of organic functions, in the restoration of body energy and some cognitive processes such as memory, thinking and language.

The physiological need of each person for sleep is variable and depend on many factors (age, sex, daily activity, sleep quality …), but in general it is recommended 7-8 hours sleep a day . People who do not rest well or don’t get enough sleep, may be affected in their daily routine and health:

  • Immune system: Lack of sleep affects the immune system, weakening it, putting our body vulnerable to many diseases. Lack of sleep not only affects the ability our immune system to work properly, but also has negative consequences in the healing of wounds.
  • Metabolism: Scientific studies have linked the lack of sleep with the onset of obesity. This relationship is due to the increased concentration of Ghrelin (hormone responsible for the appetite sensation) and decreased production of leptin (appetite inhibiting hormone) in people with lack or deprivation of sleep.
  • Cardiovascular system: Some data has shown that lack of sleep is linked with high blood pressure and other cardiovascular problems such as heart failure.
  • Endocrine system: Many hormones such as growth hormone, cortisol or sexual hormones (FSH and LH) are synthesized during sleep. Thus, the lack of sleep produces alterations in the secretion as well as the function of these hormones.
  • Nervous system: During sleep the Lymphatic system (cleaning system of NCS) has an activity 10 times higher when compared to the wakening state, which gives sleep a key role in the mental health. It is well demonstrated that lack of sleep is associated with impaired cognitive functions, and increased risk of mental illnesses such as Alzheimer’s.