Recent studies, however, have shown that several factors can interrupt this neurogenesis.[29] These include stress and prolonged sleep deprivation (more than one day).[29] The sleep disturbances encountered in AD could therefore suppress neurogenesis and thus impairing hippocampal functions.[29] This would therefore contribute to diminished memory performances and the progression of AD.[29] And progression of AD would aggravate sleep disturbances.[29] It is a second vicious circle.  
The neurodegenerative conditions are commonly related to brain structures impairment, which might disrupt the states of sleep and wakefulness, circadian rhythm, motor or non motor functioning.[22][24] On the other hand, sleep disturbances are also frequently related to worsening patient's cognitive functioning, emotional state and quality of life.[24][27][28] Furthermore, these abnormal behavioural symptoms negatively contribute to overwhelming their relatives and caregivers.[24][27][28] Therefore, a deeper understanding of the relationship between sleep disorders and neurodegenerative diseases seems to be extremely important, mainly considering the limited research related to it and the increasing expectancy of life.[22][28]
Interestingly, the glymphatic cleanrance occurs during the NREM sleep, and more specifically the NREM SWS sleep.[29][30][32] As seen previously, it is a sleep stage that decreases in normal aging.[30] So there is less glymphatic clearance and an increase in AB burden that will form the AB plaques.[32][29][30] Therefor, in AD sleep disturbances will amplify this phenomenon.
There are many possible causes of restless legs syndrome, including kidney failure, nerve disorders, vitamin and iron deficiencies, pregnancy, and some medications (such as antidepressants). Recent studies have shown a strong genetic link and researchers have been able to isolate a gene that may be responsible for at least 40% of all cases of the disorder.

Chronic sleep disorders in childhood, which affect some 70% of children with developmental or psychological disorders, are under-reported and under-treated. Sleep-phase disruption is also common among adolescents, whose school schedules are often incompatible with their natural circadian rhythm. Effective treatment begins with careful diagnosis using sleep diaries and perhaps sleep studies. Modifications in sleep hygiene may resolve the problem, but medical treatment is often warranted.[35]
Sleep apnea, obstructive sleep apnea, obstruction of the airway during sleep, causing lack of sufficient deep sleep, often accompanied by snoring. Other forms of sleep apnea are less common.[10] Obstructive sleep apnea (OSA) is a medical disorder that is caused by repetitive collapse of the upper airway (back of the throat) during sleep. For the purposes of sleep studies, episodes of full upper airway collapse for at least ten seconds are called apneas[11]

Neurodegenerative diseases have been often associated with sleep disorders, mainly when they are characterized by abnormal accumulation of alpha-synuclein, such as multiple system atrophy (MSA), Parkinson's disease (PD) and Lewy body disease (LBD).[21][22][23][24][25][26][27] For instance, people diagnosed with PD have often presented different kinds of sleep concerns, commonly regard to insomnia (around 70% of the PD population), hypersomnia (more than 50% of the PD population), and REM sleep behavior disorder (RBD) - that may affect around 40% of the PD population and it is associated with increased motor symptoms.[21][22][23][24][25][27] Importantly, RBD has been also highlighted as a strong precursor of developing dementia in PD patients over several years in prior, which seems to be a great opportunity for improving the treatments of the disease.[22][24]


In addition, an evidence-based synopses suggests that the sleep disorder, idiopathic REM sleep behavior disorder (iRBD), may have a hereditary component to it. A total of 632 participants, half with iRBD and half without, completed self-report questionnaires. The results of the study suggest that people with iRBD are more likely to report having a first-degree relative with the same sleep disorder than people of the same age and sex that do not have the disorder.[19] More research needs to be conducted to gain further information about the hereditary nature of sleep disorders.
There are many possible causes of restless legs syndrome, including kidney failure, nerve disorders, vitamin and iron deficiencies, pregnancy, and some medications (such as antidepressants). Recent studies have shown a strong genetic link and researchers have been able to isolate a gene that may be responsible for at least 40% of all cases of the disorder.
In addressing sleep disorders and possible solutions, there is often a lot of buzz surrounding melatonin. Research suggests that melatonin is useful in helping people to fall asleep faster (decreased sleep latency), to stay asleep longer, and to experience improved sleep quality. In order to test this, a study was conducted that compared subjects that had taken Melatonin to subjects that had taken a placebo pill in subjects with primary sleep disorders. Researchers assessed sleep onset latency, total minutes slept, and overall sleep quality in the Melatonin and placebo groups to note the differences. In the end, researchers found that melatonin decreased sleep onset latency, increased total sleep time, and improved quality of sleep significantly more than the placebo group.[49][50]
^ Jump up to: a b c Cao, Xiao-Lan; Wang, Shi-Bin; Zhong, Bao-Liang; Zhang, Ling; Ungvari, Gabor S.; Ng, Chee H.; Li, Lu; Chiu, Helen F. K.; Lok, Grace K. I. (2017-02-24). "The prevalence of insomnia in the general population in China: A meta-analysis". PLoS ONE. 12 (2): e0170772. doi:10.1371/journal.pone.0170772. ISSN 1932-6203. PMC 5325204. PMID 28234940.

Insomnias This type of sleep disorder involves the inability to fall asleep or stay asleep. MORE>>Hypersomnias Hypersomnias are a group of sleep disorders that causes a person to be excessively sleepy. People with a hypersomnia may fall asleep at times that are inconvenient or even dangerous, such as at work or while driving. MORE>>Sleep Related Breathing Disorders Sleep disorders that involve difficulty breathing during sleep are classified as sleep related breathing disorders. Obstructive sleep apnea is the most common disorder of this type, however there are a number of variations of sleep apnea. MORE>>Circadian Rhythm Sleep-Wake Disorders Conditions in which the sleep times are out of alignment. A patient with one of these disorders does not follow the normal sleep times at night. MORE>>Parasomnias Parasomnias are a group of sleep disorders that involve unwanted events or experiences that occur while you are falling asleep, sleeping or waking up. MORE>>Sleep Movement Disorders This classification of sleep disorders includes conditions that cause movement during or prior to sleep. These disorders can make it difficult to fall asleep or stay asleep, or to get restful sleep. MORE>>
Delayed sleep phase disorder is a condition where your biological clock is significantly delayed. As a result, you go to sleep and wake up much later than other people. This is more than just a preference for staying up late or being a night owl, but rather a disorder that makes it difficult for you to keep normal hours—to make it to morning classes, get the kids to school on time, or keep a 9-to-5 job.
Some of the biggest differences between the 2nd and 3rd editions are how the various sleep disorders were divided into categories. The 2005 edition used 3 broad categories to organize all of the sleep disorders under either dysommnias (disorders making getting to sleep or staying asleep difficult), parasomnias (disorders that intrude into the sleep process), and sleep disorders associated with a mental, neurologic, or other medical disorders (disorders whose symptoms are not primary unto themselves but caused by other conditions).
Combining results from 17 studies on insomnia in China, a pooled prevalence of 15.0% is reported for the country.[60] This is considerably lower than a series of Western countries (50.5% in Poland, 37.2% in France and Italy, 27.1% in USA).[60] However, the result is consistent among other East Asian countries. Men and women residing in China experience insomnia at similar rates.[60] A separate meta-analysis focusing on this sleeping disorder in the elderly mentions that those with more than one physical or psychiatric malady experience it at a 60% higher rate than those with one condition or less. It also notes a higher prevalence of insomnia in women over the age of 50 than their male counterparts.[61]

Histamine plays a role in wakefulness in the brain. An allergic reaction over produces histamine causing wakefulness and inhibiting sleep[37] Sleep problems are common in people with allergic rhinitis. A study from the N.I.H. found that sleep is dramatically impaired by allergic symptoms and that the degree of impairment is related to the severity of those symptoms [2]s[38] Treatment of allergies has also been shown to help sleep apnea.[39]
At the same time, it has been shown that memory consolidation in long-term memory (which depends on the hippocampus) occurs during NREM sleep.[29][33] This indicates that a decrease in the NREM sleep will result in less consolidation and therefore poorer memory performances in hippocampal-dependent long-term memory.[29][33] This drop in performance is one of the central symptoms of AD.[29]  
Idiopathic hypersomnia: a chronic neurological disease similar to narcolepsy in which there is an increased amount of fatigue and sleep during the day. Patients who suffer from idiopathic hypersomnia cannot obtain a healthy amount of sleep for a regular day of activities. This hinders the patients' ability to perform well, and patients have to deal with this for the rest of their lives.[15]

A catch-all term for the inability to fall or stay asleep, sleeplessness is -- as sufferers know -- a very serious problem. It's sleeplessness whenever something, whether it's physical pain, anxiety, or an underlying condition, prevents you from falling asleep within a reasonable amount of time or staying asleep long enough to achieve a good night's sleep.
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