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* From the Division of Pulmonary, Critical Care and Sleep Medicine (Drs. Phillips and Mannino), University of Kentucky College of Medicine, Lexington, KY; National Sleep Foundation (Mr. Britz), Washington, DC; and Department of Neurology (Dr. Hening), UMDNJ-Robert Wood Johnson Medical School, New Brunswick, NJ.
Correspondence to: Barbara Phillips, MD, MSPH, FCCP, Fifth Floor, Kentucky Clinic, Division of Pulmonary, Critical Care and Sleep Medicine, UKMC, 800 Rose St, Lexingon, KY 40536-0028; e-mail: Bphil95{at}aol.com
Abstract
Purpose: The purpose of this analysis was to investigate the prevalence and correlates of restless legs syndrome (RLS) symptoms in the 2005 National Sleep Foundation (NSF) Sleep in America 2005 Poll. The NSF poll is an annual telephone interview of a random, representative sample of US adults.
Methods: The NSF 2005 poll included 1,506 adults. Their mean age was 49 years, and 775 were women.
Results: Symptoms of RLS that included unpleasant feelings in the legs for at least a few nights a week, which were worse at night, were reported by 9.7% of individuals in this poll, including 8% of men and 11% of women. Those from the northeast United States were much less likely to be at risk than those from other regions of the country (p < 0.05). Those who were unemployed (p < 0.05) or smoked daily (p < 0.5) were more likely to be at risk for RLS, as were those with hypertension, arthritis, gastroesophageal reflux disease, depression, anxiety, and diabetes (p < 0.05 for all). Adults who were at risk for RLS appeared to also be at increased risk for sleep apnea and insomnia (p < 0.05), and were more likely to stay up longer than they planned, to take longer than 30 min to fall asleep, to drive when drowsy, and to report daytime fatigue than those who were not at risk (p < 0.05 for all). They were also more likely to report being late to work, missing work, making errors at work, and missing social events because of sleepiness than other respondents in the poll (p < 0.05 for all).
Conclusions: RLS is significantly associated with medical and psychiatric conditions, other sleep disorders, unfavorable lifestyle behaviors, and adverse effects on daytime function. Chest physicians who practice sleep medicine need to be able to identify and manage RLS, which is prevalent and is associated with considerable morbidity.
Key Words: anemia • arousals • cigarette smoking • dyssomnias • geography • insomnia • iron • neurological/sleep movement disorder • poll • sleep • sleepiness • twitching
Restless legs syndrome (RLS) is a common, debilitating condition. The prevalence of RLS is estimated to be about 10% and increases with age.1234 Women appear to be at increased risk,4 as do individuals with certain chronic conditions, including renal failure and anemia.3456 The pathophysiology of RLS is incompletely understood, but it probably results from derangements in dopamine and iron metabolism,789 and has a genetic component.51011 It appears likely that a majority of individuals with RLS do not seek or receive medical attention.12 Because RLS is a prevalent sleep disorder, it is likely to be encountered by pulmonologists who are practicing sleep medicine.
The diagnosis of RLS is based on clinical grounds and requires an uncomfortable urge to move the legs that is worse with activity, is relieved by inactivity, and is worse at night.13 Supporting evidence for the diagnosis includes a response to dopaminergic agents, a family history of the disorder, and periodic limb movements (PLMs). PLMs are repetitive, highly stereotypical movements occurring during sleep that are frequently associated with RLS. However, the significance of PLMs is very controversial; PLMs are very prevalent and nonspecific, and are not necessary or sufficient to make the diagnosis of RLS.14 The aims of this analysis were to report the prevalence and correlates of symptoms of RLS in the 2005 National Sleep Foundation (NSF) poll.
Materials and Methods
NSF Poll
Data pertaining to the prevalence of RLS in this report are from the 2005 NSF annual Sleep in America poll. The NSF is an independent nonprofit organization that is dedicated to improving public health and safety by achieving an understanding of sleep and sleep disorders, and by supporting education, sleep-related research, and advocacy (www.sleepfoundation.org). Established in 1990, the NSF relies on voluntary contributions as well as grants from foundations, corporations, government agencies, and other organizations to support its programs. The NSF conducts Sleep in America polls annually, with the release of the results timed to coincide with National Sleep Awareness Week, which is the week before the change to Daylight Savings time in the spring. The topics and questions included in the poll are selected by a subset of volunteers and board members, and there is no commercial or industry influence on this poll. Since the diagnosis of RLS is made on the basis of a history of uncomfortable leg sensations that are worsened with inactivity and occur at night, it is possible and appropriate to learn about the prevalence and risks of this cluster of symptoms in a survey of sleep habits. To date, no random sample of RLS prevalence specifically in the US population has been undertaken.
A random sample of telephone numbers was purchased, and quotas were established by region and age, based on US Census household data. The total sample size was designed to be 1,500 participants. Telephone interviews were conducted between September 20 and November 7, 2004, resulting in a random sample of 1,506 adults. The interviews averaged 20 min in duration. In order to qualify for inclusion in the survey, participants had to be community-dwelling (ie, not residing in institutions), 
18 years of age, and living within the continental United States. Interviewers explained the poll to participants by reading a script, which stated, "I am calling on behalf of the National Sleep Foundation to conduct a survey about sleep among Americans. This is not a sales call; it is a national research survey. It will take a few minutes of your time and your responses will be kept strictly confidential." Respondents gave verbal consent to participate in this voluntary study, and their consent was further demonstrated by their willingness to answer the questions asked. Participants were told that they could refuse to answer any question. A total of 26,847 households were called; 4,343 households did not answer repeated phone calls, and 4,168 potential participants refused. Thus, the participation rate calculated by taking the number of completed interviews divided by the number of completed interviews plus the number of contacted households who refused participation or did not qualify was 23%. Institutional review board approval was not required to conduct or publish the results of a poll without any individual identifying information that is conducted by a nonprofit independent organization. There was no compensation for participation.
Approximately 80% of the interviews were conducted on weekdays between 5:00 PM and 8:00 PM, on Saturdays between 10:00 AM and 4:00 PM, and on Sundays between 4:00 PM and 8:00 PM by professional interviewers from WB&A Market Research (Annapolis, MD) on behalf of the NSF.
To address the prevalence of those at risk for RLS, we chose to use one of the standard questions developed by The International Restless Legs Syndrome Study Group to assess RLS prevalence in surveys: "In the past year, according to your own experiences or what others tell you, how often did you have unpleasant feelings in your legs like creepy, crawly or tingly feelings at night with an urge to move when you lie down to sleep?" The possible responses were as follows: every night or almost every night; a few nights a week; a few nights a month; rarely; and never.
Those who answered that they had these feelings at least a few nights a week were asked the following question: "Would you say these feelings in your legs are worse, about the same as, or better at night or in the evening compared to other times of day?" The response choices were as follows: worse at night; about the same as; or better at night. Individuals were designated as being likely to have RLS if they endorsed unpleasant feelings at least a few nights a week and said that those feelings were worse at night.
Participants were also asked "In the past year, according to your own experiences or what others tell you, how often did you move your body frequently or have twitches often during the night?" In addition, they were queried about usual bedtimes and wake times on weekdays vs weekends and their usual number of hours of sleep on those days. Respondents were also asked how often in the past year they had difficulty falling asleep, were awake a lot during the night, woke up too early and could not get back to sleep, woke up feeling unrefreshed, snored, had pauses in breathing during sleep, or how often they feel tired or fatigued or not up to par during wake time. Frequency responses for these items were every night or almost every night, a few nights a week, a few nights a month, rarely, or never. Persons reporting these symptoms a few nights a week or more were labeled as having the particular sleep problems/disorder.
The risk of having sleep apnea was estimated by use of the Berlin Questionnaire,15 which was embedded into the poll and which correlates reasonably well with polysomnography findings. Similarly, respondents were asked whether they had ever been told by a doctor they had the following medical conditions (yes, no): heart disease or high BP; arthritis; diabetes; lung disease; heartburn or gastroesophageal reflux disease; or anxiety disorder or depression. Demographic data were also gathered. Regions of residence were defined as follows: Northeast (Connecticut, Massachusetts, Maine, New Hampshire, New Jersey, New York, Pennsylvania, Rhode Island, and Vermont); Midwest (Iowa, Illinois, Indiana, Kansas, Michigan, Minnesota, Missouri, North Dakota, Nebraska, Ohio, South Dakota, and Wisconsin); South (Alabama, Arkansas, Washington, DC, Delaware, Florida, Georgia, Kentucky, Louisiana, Maryland, Mississippi, North Carolina, Oklahoma, South Carolina, Tennessee, Texas, Virginia, and West Virginia); and West (Arizona, California, Colorado, Idaho, Montana, New Mexico, Nevada, Oregon, Utah, Washington, and Wyoming).
Analysis of NSF Poll
Statistical analyses included 
2 tests of associations for age and sex group differences in the percentage for each sleep problem. Those who endorsed symptoms of uncomfortable leg sensations every night, almost every night, or a few nights a week or more and who reported that these symptoms were worse at night were designated as being "at risk for RLS." Stepwise multiple logistic regression models were used to predict the odds for each sleep problem according to significantly associated medical conditions after adjusting for age, gender, and an existing diagnosis of a sleep disorder. A multidimensional multiple logistic regression for the odds of reporting one or more sleep problems was derived from the various indexes for diseases, health, and behavioral characteristics. Analyses were performed with a statistical software package (SAS; SAS Institute; Cary, NC).
Results
In the total poll sample, a similar number of women (n = 775) and men (n = 731) were interviewed, and their mean age was 49 years. Sixty-two percent were married, 33% were single, and 5% were living with someone ("partnered"). Consistent with the US population, 36% lived in the south, 21% in the west, 24% in the midwest, and 19% in the northeast; 84% were white/white and 16% were minorities; and 52% were employed full-time and, of those, 80% worked regular day shifts.
Fifteen percent of respondents reported an uncomfortable urge to move their legs a few nights a week, and 8% reported these sensations every night or almost every night. Of those reporting having the sensations at least a few nights a week, 65% reported that the feelings were worse at night. Thus, 9.7% of individuals in this poll satisfied the criteria for RLS that have been used in previous population-based surveys. Of these individuals, 8% were men and 11% were women. Of those who met the more stringent criteria of reporting the leg sensations every night or almost every night, and whose sensations were worse at night, 5% were men and 6% were women. A striking finding of the poll results was the marked regional variation in prevalence of RLS symptoms (Fig 1 ). Those patients from the northeastern United States were statistically less likely to be at risk for RLS than those from other areas (p < 0.05). Those from the south were about twice as likely to have frequent or occasional symptoms of RLS than those from any other region; when we analyzed the data comparing those patients who had uncomfortable leg sensations every night or almost every night, those from the south were statistically significantly more likely than those from other geographic areas to be in this group (p < 0.05).
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We identified persons at risk for sleep apnea in this survey by use of the Berlin questionnaire.15 Overall, 26% of respondents were at risk for sleep apnea. Of those who were at risk for RLS, 52% were at risk for sleep apnea, compared with 23% of those who were not at risk for RLS (p < 0.05).
There were also striking associations for those patients who were at risk for RLS and sleep behaviors; those who were at risk for RLS were more likely to sleep < 6 h a night, to endorse symptoms of insomnia, and to have body twitches/movements (p < 0.05). In addition, they were more likely to stay up longer than they had planned more than a few nights a week, to take > 30 min to fall asleep, and to report daytime fatigue than those who were not at risk for RLS (p < 0.05).
Those patients who endorsed RLS symptoms appeared to experience significantly more daytime problems (Fig 2 ), including being late to work, making errors at work, or missing work because of sleepiness. They also reported missing events and driving drowsy more frequently than did other respondents in the poll (p < 0.05 for all). Fifty-five percent of men and 45% of respondents reported twitching or moving their bodies frequently at night, and those who did so were more likely to be from the south.
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New findings in this study are a reduced risk of RLS symptoms for those in the northeastern United States, and the association of the risk of RLS with the risk for sleep apnea and impaired daytime performance.
The NSF 2005 poll shows that, consistent with other studies, about 10% of the US adult population reports RLS symptoms. In addition, this study also demonstrates interesting regional variations in the prevalence of RLS symptoms; we think that this is the first time this has been reported. Specifically, RLS symptoms are less prevalent in the northeastern United States than in other parts of the country. There are several possible explanations for this, including that several of the factors that increase the risk of RLS (eg, obesity or cigarette smoking) are more prevalent in other areas of the country. Another possibility, however, is regional variation in the prevalence of iron deficiency. Iron deficiency is strongly associated with RLS symptoms.1617 A brief review of the Third National Health and Nutrition Examination Survey18 demonstrated a prevalence of anemia of 8.2%, 6.9%, 5.8%, and 5.6% for the south, northeast, west, and midwest, respectively. Obviously, these data are not comparable, for many reasons, including that the NSF survey is a poll with a low response rate and is subject to significant sampling errors. It is also very current, having been conducted in late 2004, while the data from the Third National Health and Nutrition Examination Survey were collected more than a decade ago. The age ranges and definitions of geographic areas covered by each study are different. Yet, the findings are striking, since both anemia and RLS symptoms appear to be more prevalent in the south. While this association can be considered hypothesis-generating at best, it supports the biological basis of iron deficiency as a factor in the pathogenesis RLS.
We found a tendency for the endorsement of RLS symptoms to increase with age until the age of 65 years, as has been reported by others,419 and we noted a trend toward increased prevalence in women compared with men. We also confirmed the association between RLS symptoms and both cigarette smoking and being overweight.2 There was a strong association between physical and mental health problems and RLS symptoms, as has consistently been reported by others.34
Our findings both differ from and support the results from the RLS Epidemiology, Symptoms, and Treatment (REST) study,19 which reported a 5% prevalence of weekly symptoms and a 2.7% prevalence of at least twice weekly symptoms that were moderately or severely distressing. The REST study involved 15,391 completed questionnaires from several western European countries and the United States. The REST study employed six questions relative to RLS (in addition to prescreening and postscreening questions), so the resulting RLS prevalence estimate is, not unexpectedly, more conservative. On the other hand, the prevalence of about 10% that we found in the current study is very similar to that reported in other large-scale population studies.1234 The findings of the NSF 2005 poll in comparison to the REST study highlight the importance of frequency criteria. If RLS risk is defined to include a requirement for symptoms every night or almost every night, as well as for symptoms being worse at night, the prevalence is lower. Most clinical definitions of RLS do not have specific frequency criteria, which has probably contributed to some variance in prevalence estimates. This may also be part of the reason that RLS has been diagnosed and treated in far < 10% of the population, as it is likely that many physicians and patients are unwilling to undertake long-term treatment for symptoms that are not frequent.
The REST study included 6,014 US participants, but information about regional variation in symptoms is not included in the report. Although the REST study included some information about quality of life based on the Medical Outcomes Study 36-item short form, most participants did not complete this part of the survey; the REST investigators were not able to extensively correlate RLS symptoms with health or lifestyle.
The endorsement of twitching or frequent body movements in the current study was so frequent as to render it a nonspecific finding. We cannot draw any conclusions based on this reported symptom in this study, other than to suggest that asking about body twitching may not be useful in the clinical evaluation of patients.
This NSF survey confirmed the 10% prevalence of RLS that has been frequently reported in the literature, using a definition that requires uncomfortable leg sensations a few nights a week or more that are worse at night. These findings confirm that RLS symptoms are associated with impaired daytime function, with sleep apnea and other sleep complaints, and with unhealthy lifestyles. Identifying and treating RLS may improve sleep quality and daytime function.
Footnotes
Abbreviations: NSF = National Sleep Foundation; PLM = periodic limb movement; REST = Restless Leg Syndrome Epidemiology, Symptoms, and Treatment; RLS = restless legs syndrome
Received for publication May 22, 2005. Accepted for publication September 12, 2005.
References
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