cells is correlated with severity of PD. However, there is no reason to believe that narcolepsy patients are at increased risk of developing Parkinson's disease. According to study author Jerry Siegel, PhD, professor of psychiatry and biobehavioral sciences at the Semel Institute for Neuroscience and Human Behavior at UCLA, the cause of the hypocretin cell loss in Parkinson's is likely to be quite different from the cause of this cell loss in narcolepsy.
There may also be a connection between REM sleep behavior disorder (dream–enacting behaviors during sleep) and the subsequent development of Parkinson’s disease. In one study, researchers found that up to 75% of patients with REM behavior disorder went on to develop a Parkinsonian disorder, presumably Parkinson’s disease. In addition, people with Parkinson’s disease are at higher risk for restless legs syndrome (RLS) and periodic leg movement disorder, two conditions that may seriously disrupt sleep. However, there is no evidence that RLS or PLMD are risk factors for Parkinson’s disease.
In addition to sleep problems, people with Parkinson's disease often experience sleepiness during the daytime. In fact, one study found daytime sleepiness in 76% of Parkinson’s patients. These sleep-related symptoms can have a major impact on quality of life for Parkinson’s patients and treatment for these problems should be integrated with their therapeutic regimens.
Because of the mystery surrounding the origin of Parkinson’s disease, a great deal of research has been done on this problem. We know that the symptoms of Parkinson’s are primarily the result of the gradual loss of dopaminergic cells (neurons that release dopamine, a neurotransmitter that activates dopamine receptors) in the brain. Some Parkinson’s research has focused on the relationship between Parkinson’s and both the timing and duration of sleep. For example, a 12-year study by researchers at the National Institute of Environmental Health Sciences of the U.S. National Institutes of Health found that among nearly one million nurses, working the night shift was associated with a lower risk of Parkinson’s disease. They also found that long sleep (sleeping 9 hours or more) was associated with a higher risk.
People with Parkinson’s disease have a