Original article

Prevalence, severity and risk factors of restless legs syndrome

in the general adult population in two Scandinavian countries

Bjørn Bjorvatna,i,*, Lena Leissnerb, Jan Ulfbergc, Jens Gyringd, Merete Karlsborge,

Lisbeth Regeure, Havard Skeidsvollf,i, Inger Hilde Nordhusg,i, Stale Pallesenh,i

aDepartment of Public Health and Primary Health Care, University of Bergen, Kalfarveien 31 N-5018, Bergen, NorwaybSleep Unit, Department of Neurology, University Hospital Orebro, Orebro, Sweden

cSleep Disorders Center, Avesta Hospital, Avesta, SwedendHammel Neurocenter, Arhus County, Denmark

eDepartment of Neurology, Bispebjerg Hospital, DenmarkfDepartment of Neurology, Haukeland University Hospital, Jonas Liesvei, Norway

gDepartment of Clinical Psychology, University of Bergen, NorwayhDepartment of Psychosocial Science, University of Bergen, Norway

iNorwegian Competence Center for Sleep Disorders, Norway

Received 16 November 2004; received in revised form 11 February 2005; accepted 4 March 2005

Abstract

Background and Purpose: To estimate prevalence and severity (using the International Restless Legs Syndrome Study Group Rating Scale

(IRLS)) and to identify risk factors of restless legs syndrome (RLS).

Patients and Methods: Population-based cross-sectional study; 2005 randomly selected adults 18 years and above participated in a telephone

interview in Norway and Denmark, employing the next-birthday technique.

Results: Of the cross-section, 11.5% fulfilled the diagnostic criteria for RLS. Half of these reported the symptoms as moderate to very severe.

Mean duration of the complaint was 10 years. Prevalence was higher in females than in males (13.4 vs 9.4%) and lowest in the youngest age

group (18–29 years, 6.3%). From 30 years and above, no clear age-related difference was seen. Main predictors of RLS were insomnia

(odds ratios: 1.71–3.16) and symptoms of periodic limb movements in sleep (3.20–7.85). The response rate was 47%, making the results

less reliable.

Conclusions: This study indicates that there is a high occurrence of RLS among adults. Main predictors are insomnia and periodic limb

movements in sleep.

q 2005 Elsevier B.V. All rights reserved.

Keywords: Restless legs syndrome; Prevalence; Severity scale; IRLS; Risk factors; Insomnia; PLMS

1. Introduction

Restless legs syndrome (RLS) is a common, but often

misdiagnosed, underdiagnosed or undiagnosed neurological

movement disorder [1]. RLS can be a primary disorder, or it

can be secondary to conditions such as iron deficiency,

1389-9457/$ - see front matter q 2005 Elsevier B.V. All rights reserved.

doi:10.1016/j.sleep.2005.03.008

* Corresponding author. Tel.: C47 55 58 61 00; fax: C47 55 58 61 30.

E-mail address: bjorn.bjorvatn@isf.uib.no (B. Bjorvatn).

pregnancy, or end-stage renal disease. The syndrome is

usually a chronic condition, and in general the severity and

frequency of symptoms increase with age [2]. The syndrome

was first described and named in 1945, and in 1995 the

International Restless Legs Syndrome Study Group devel-

oped standardized criteria for the diagnosis of RLS. These

criteria were recently modified [2]. The essential criteria for

the syndrome are (1) an urge to move the legs, usually

accompanied or caused by uncomfortable and unpleasant

sensations in the legs; (2) the urge to move or unpleasant

sensations begin or worsen during periods of rest or

inactivity such as lying or sitting; (3) the urge to move or

Sleep Medicine 6 (2005) 307–312

www.elsevier.com/locate/sleep

B. Bjorvatn et al. / Sleep Medicine 6 (2005) 307–312308

unpleasant sensations are partially or totally relieved by

movement, such as walking or stretching, at least as long as

the activity continues; and (4) the urge to move or

unpleasant sensations are worse in the evening or night

than during the day or only occur in the evening or night. All

four of these criteria must be met for RLS to be diagnosed

[2]. There are several supportive clinical features in

addition, i.e. positive family history, response to dopamin-

ergic treatment, and periodic limb movements. These are

not essential to the diagnosis, but their presence can help

resolve any diagnostic uncertainty. The severity of RLS can

be measured using the recently developed and validated

International Restless Legs Syndrome Study Group Rating

Scale (IRLS) [3].

To date, there are few population-based epidemiologi-

cal studies, especially investigating risk factors. Most

studies are limited in size or use inconsistent ascertainment

tools [2]. Despite these limitations, most studies report

prevalences of RLS in the range of 5–15% [4]. There is a

need for more population-based epidemiological studies in

different countries, based on the updated diagnostic

criteria.

The aim of the present study was to estimate the

prevalence and severity of RLS in two Scandinavian

countries, Norway and Denmark. In addition, several

demographic and sleep-related variables were examined in

order to identify risk factors of RLS. The present study

utilized the recently updated diagnostic criteria and the

newly developed rating scale for severity (IRLS).

Table 1

Questions about sleep, depressive mood, etc., and their response

alternatives employed in the study

1. During the past 4 weeks, how often did you experience difficulty falling

asleep or maintaining sleep? (never, sometimes, usually, always).

2. During the past 4 weeks, how often did you experience sleep difficulties

or daytime sleepiness that interfered with your daily activities? (never,

sometimes, usually, always).

3. During the past 4 weeks, do you know (possibly through others) how

often you have had repeated rhythmic leg jerks or leg twitches during

your sleep? (never, sometimes, usually, always).

4. During the past 4 weeks, do you know (possibly through others) how

often you have had a loud and disturbing snoring? (never, sometimes,

usually, always).

5. During the past 4 weeks, do you know (possibly through others) how

often you have had breathing pauses or stopped breathing in your sleep?

(never, sometimes, usually, always).

6. During the past 4 weeks, how often have you felt depressed most of the

day, or experienced diminished interest or pleasure in activities you

usually enjoy? (never, sometimes, usually, always).

7. Are you being treated for high blood pressure? (yes, no)

8. Are you being treated for heart disease? (yes, no)

2. Materials and methods

2.1. Procedure

The study was part of a telephone interview conducted by

opinion-research institutes (Opinion in Norway, Hermelin

in Denmark), employing the next-birthday technique. In the

next-birthday technique the interviewer asks to speak to the

adult member of the household who has the next birthday.

This technique constitutes a procedure of randomly

selecting individuals within a household, preventing

potential selection bias [5]. The sample was drawn

randomly from a survey population, consisting of each

country’s register of phone numbers. All phone numbers

were called up to six times. The response rate (i.e. accepting

participation) among those who were reached was 46.7% in

Norway and 47.0% in Denmark. The study was introduced

as a nation-wide research survey by the opinion-research

institute. In general, the subjects accept or reject partici-

pation before being asked specific questions. In Norway, the

questions were part of a larger omnibus, including a total of

57 questions. In Denmark, only the reported questions were

asked. These opinion-research institutes claim that their

procedures secure that the sample matches the targeted

population.

2.2. Participants

A total of 2005 randomly selected adults, 1000 from

Norway and 1005 from Denmark, stratified by the number

of inhabitants in each county in the respective country,

accepted participation in the study. In all, the sample

consisted of 1025 females and 980 males, and the mean age

was 46.6 years (SDZ17.8, rangeZ18–99 years). The

frequency distribution in the different age groups was

21.1% in the 18–29 group, 29.1% in the 30–44 group, 24.4%

in the 45–59 group, and 25.4% in the 60 and above group.

Of the total sample, 13.2% reported no education sub-

sequent to mandatory schooling, while 29.9% reported one

to three years, 32.3% reported four to six years, and 24.5%

reported more than six years of education subsequent to

mandatory schooling. Furthermore, 18.8% of the sample

reported a household income of less than 300.000

NOK/DKK (7 NOK/DKKZ$ 1), 32.4% reported between

300.000 and 599.000 NOK/DKK, 25.2% reported 600.000

NOK/DKK or above, whereas 23.6% refused to report their

household income.

2.3. Material

In addition to demographic and other background

information (age, gender, education, place of residence,

household income), the participants were asked several

questions concerning sleep, depressive mood, etc. (Table 1).

Some of these questions were adapted from the Global

Sleep Assessment Questionnaire [6]. The participants were

questioned about RLS, using the updated diagnostic criteria,

and only those who answered yes to all four diagnostic

criteria were defined as RLS subjects. No time frame for

experiencing RLS symptoms was given. RLS subjects were

subsequently asked about severity using the International

B. Bjorvatn et al. / Sleep Medicine 6 (2005) 307–312 309

Restless Legs Syndrome Study Group Rating Scale (IRLS),

version 2.1. This subjective scale consists of ten questions,

including five items pertaining to symptom frequency and

intensity and five items addressing the impact of symptoms

on aspects of daily living and sleep. The designated time

frame for experiencing RLS symptoms is during the

previous week. We used the appropriate translation of

the severity scale into Norwegian and Danish, obtained

from Mapi Research Institute, as suggested by Hening and

Allen [7]. In addition to questions about severity,

participants were asked how long they have had RLS

(one year or less was coded as 1 year), about ‘doctor-

seeking’ behavior for RLS, and about family history of RLS.

2.4. Statistics

The data analyses were performed with SPSS version

11.5 (SPSS, Inc., 2002). The results were weighted

according to the population distribution of gender and age,

in order to correct for potential divergence between the

sample and the distribution of age and gender in the general

population of Norway and Denmark, respectively.

Differences in the prevalence of RLS between gender, age

groups and the other variables were explored using

chi-square statistics. A univariate weighted logistic

regression procedure was conducted in order to investigate

whether demographic and other variables were related to

RLS. Gender and treatment for blood pressure and heart

disease comprised dichotomous variables, whereas the rest

of the predictors (age group, education, family income,

insomnia, excessive daytime sleepiness, symptoms of

periodic limb movements in sleep, loud snoring, breathing

pauses in sleep and depressive mood) all were operationa-

lized along a four-point scale. Where the 95% confidence

interval did not include 1.00, the odds ratios were

considered as statistically significant. The significant

predictors from the univariate analysis were then entered

into a multivariate analysis in order to identify the unique

significant predictors of RLS.

3. Results

The weighted mean overall prevalence of RLS in the

general adult population was 11.5% (95% CIZ10.0–13.0).

RLS symptoms were reported for a mean duration of 10.1

years (SDZ9.8, rangeZ1–45 years; medianZ6 years).

Less than one-third reported seeking professional (medical)

help for the RLS symptoms. However, seeking medical help

was clearly related to the severity of RLS (100% of the

subjects with very severe symptoms had contacted their

doctor about RLS; 82% of subjects with severe symptoms;

46% of subjects with moderate severity; 10% of subjects

with mild severity; and 8% of subjects reporting no

symptoms during the previous week had contacted their

doctor). The reason for not seeking professional help was

examined on a three-point scale. Of the subjects, 13.7%

reported that they did not think the doctor could help with

their symptoms, 66.1% reported that the symptoms were not

severe enough to involve a doctor, and 20.3% reported

‘other reasons’. RLS was significantly more prevalent in

Norway than in Denmark (14.3% and 8.8%, respectively,

P!0.001). A family history of RLS was reported by 41.8%.

Although a family history was more commonly reported in

Norway than in Denmark (45.1% versus 35.7%), this

difference was not significant (PZ0.2).

RLS severity during the last week ranged from none to

very severe, with an average value in the moderate category.

Twenty-nine participants did not complete all ten questions

of the severity scale. Thus, RLS severity scaling was based

on the remaining 193 subjects. Very severe symptoms were

reported by 3.1%, severe symptoms by 11.6%, moderate

severity by 33.7%, mild severity by 44.8%, and no

symptoms (in the previous week) by 6.8%.

Table 2 reports the percentages of subjects with RLS in

different gender and age groups, in addition to the RLS

prevalence in the other sleep-related variables. Chi-square

tests between the different age groups showed that RLS

prevalence was significantly lower in the lowest age group

(18–29 years) compared to all other age groups, whereas no

significant difference in prevalence was seen among the

other age groups. Thus, we did not find an increasing RLS

prevalence from the 30–44 group and up. The prevalence of

RLS was not significantly related to level of education,

number of people in the household, household income, or

being treated for high blood pressure or heart disease

(data not shown).

Table 3 reports the results from the univariate logistic

regression analysis comprising 13 predictor variables and

RLS as the criterion variable. In all, eight of the 13 predictor

variables showed a significant relationship with RLS. These

were gender, age group, insomnia, excessive daytime

sleepiness, symptoms of periodic limb movements in

sleep, loud snoring, breathing pauses in sleep, and

depressive mood. These eight variables were then entered

into a multivariate logistic regression analysis. This multi-

variate analysis showed that age group, insomnia, excessive

daytime sleepiness, and periodic limb movements in sleep

maintained a significant relationship with RLS (Table 3).

4. Discussion

The overall prevalence of RLS in the general adult

population was 11.5%. Although the response rate was low,

making the results less reliable, this percentage indicates

that RLS is a very common condition. The prevalence in

these Scandinavian countries is similar to that reported in

other countries, ranging from 5 to 15% [4,8,9]. The

prevalence was higher in Norway, compared to Denmark,

but we do not have an explanation for this finding. The data

collection procedure was identical in both countries.

Table 2

The prevalence of restless legs syndrome (RLS) in different gender, age

groups, and other sleep-related variables

Total number

of respondents

RLS (%) Chi-square test

(P-value)

Gender 0.006

Male 945 9.4

Female 982 13.4

Age 0.002

18–29 years 396 6.3

30–44 years 571 12.6 0.001a

45–59 years 473 14.2 !0.001a

60 years and

above

488 11.9 0.005a

Insomnia !0.001

Never 1031 6.7

sometimes 580 14.0

Usually 193 24.4

Always 118 20.3

Excessive daytime sleepiness

Never 1174 8.1

sometimes 545 17.8 !0.001

Usually 120 17.5

Always 49 14.3

Periodic limb movements in sleep !0.001

Never 1495 8.2

sometimes 205 25.4

Usually 37 51.4

Always 18 16.7

Loud snoring 0.006

Never 986 9.5

sometimes 419 14.3

Usually 177 13.6

Always 115 18.3

Breathing pauses in sleep 0.050

Never 1584 10.7

sometimes 61 18.0

Usually 16 12.5

Always 9 33.3

Depressive mood 0.001

Never 1451 10.1

sometimes 396 15.4

Usually 58 22.4

Always 17 5.9

a Significant different from the 18–29 group. No differences were seen

between the other age groups.

Table 3

Weighted univariate and multivariate logistic regression analysis compris-

ing several predictor variables and restless legs syndrome (RLS) as the

criterion variable

Predictor Odds ratio 95% CI Odds ratio 95% CI

Univariate Multivariate

Gender

Male 1.00 1.00

Female 1.49 1.12–1.98 1.34 0.93–1.91

Age group

18–29 years 1.00 1.00

30–44 years 2.15 1.34–3.47 1.71 0.99–2.94

45–59 years 2.48 1.54–4.02 2.12 1.22–3.69

60 years and

above

2.00 1.23–3.27 1.24 0.68–2.26

Education

None 1.00

1–3 years 1.09 0.69–1.71

4–6 years 0.95 0.60–1.49

More than 6

years

0.85 0.53–1.39

People in

household

One 1.00

Two 1.21 0.81–1.79

Three–four 1.04 0.70–1.55

Five or

more

0.96 0.53–1.72

Household

income

Less than

300,000

NOK

1.00

300,000–

599,900

NOK

1.33 0.89–1.99

600,000

NOK or

above

1.07 0.70–1.65

Insomnia

Never 1.00 1.00

Sometimes 2.26 1.61–3.16 1.71 1.13–2.58

Usually 4.49 2.98–6.76 3.16 1.24–5.40

Always 3.56 2.14–5.93 2.75 1.36–5.56

Excessive daytime sleepiness

Never 1.00 1.00

Sometimes 2.46 1.82–3.33 1.84 1.24–2.74

Usually 2.46 1.47–4.10 1.78 0.93–3.42

Always 1.92 0.85–4.35 0.86 0.24–3.15

Period limb movement in sleep

Never 1.00 1.00

Sometimes 3.83 2.66–5.52 3.20 2.09–4.91

Usually 11.46 5.87–22.38 7.85 3.27–18.86

Always 2.09 0.57–7.64 3.29 0.63–17.31

Loud snoring

Never 1.00 1.00

Sometimes 1.60 1.13–2.26 1.38 0.91–2.09

Usually 1.50 0.93–2.42 1.19 0.66–2.15

Always 2.14 1.27–3.58 1.96 0.96–4.02

Breathing pauses in sleep

Never 1.00 1.00

Sometimes 1.80 0.91–3.54 1.24 0.57–2.73

Usually 0.93 0.18–4.86 0.69 0.12–4.08

Always 4.50 1.11–18.31 1.38 0.21–9.32

(continued on next page)

B. Bjorvatn et al. / Sleep Medicine 6 (2005) 307–312310

A family history of RLS was more commonly reported in

Norway, and although this finding did not reach signifi-

cance, this may possibly influence prevalence.

The newly developed International Restless Legs

Syndrome Study Group Rating Scale (IRLS) showed that

about half of the RLS sufferers reported moderate to very

severe symptoms, whereas the other half report less

symptoms, during the previous week. To our knowledge,

this is the first study to use the severity scale in an

epidemiological setting, selected on a nation-wide basis.

The quality of RLS management in the Scandinavian

countries is far from optimal. A postal study among general

practitioners in Denmark, Norway and Sweden showed that

there is a need for establishing a common strategy, both in

regards to diagnosis and treatment of RLS, based on

Table 3 (continued)

Predictor Odds ratio 95% CI Odds ratio 95% CI

Univariate Multivariate

Depressive mood

Never 1.00 1.00

Sometimes 1.62 1.17–2.23 0.99 0.65–1.51

Usually 2.50 1.31–4.77 1.01 0.40–2.53

Always 0.82 0.15–4.55 0.41 0.04–4.51

Treated for high blood pressure

Yes 1.00

No 1.09 0.71–1.68

Treated for heart disease

Yes 1.00

No 0.72 0.41–1.26

B. Bjorvatn et al. / Sleep Medicine 6 (2005) 307–312 311

internationally accepted guidelines and evidence-based

medicine (Leissner et al., unpublished data). Interestingly,

less than one-third of the RLS sufferers in the present study

reported seeking professional help and about 14% did not

think the doctor could help with their RLS symptoms.

However, our study clearly indicates that the more severe

the RLS symptoms, the more likely people are to seek

professional help.

The prevalence of RLS was higher in females than in

males, as has been reported before [4,8,10]. Many studies

suggest that RLS prevalence increases with age [4,8,10,11].

In the present study, RLS prevalence was significantly lower

in the lowest age group (18–29 years) compared to the other

age groups. There were, however, no differences in

prevalence between the other age groups. This was

surprising, even though some other studies also report no

increase with age [12,13]. One factor to consider is that

some patients suffering from severe RLS may experience

symptoms throughout the day [14], and may thus, in the

present epidemiological study, actually not fulfill the

diagnostic criteria. More than one hundred respondents

failed to answer yes to the fourth diagnostic criterion, even

though they had answered yes to the other RLS questions.

One may assume that the older the subjects are the more

likely to experience severe RLS and thus have symptoms

throughout the day. However, there was no age-related

difference in the response to the fourth diagnostic criterion.

The prevalence of RLS was higher in subjects complain-

ing of insomnia, excessive daytime sleepiness, periodic

limb movements in sleep, loud snoring, breathing pauses in

sleep, and depressive mood (Table 2). In some instances it is

likely to assume that RLS may cause these conditions, i.e.

insomnia, whereas in other instances RLS may be the result

of the disease or the treatment of the disease, i.e. depression.

Logistic regression analysis indicated that the main

predictors of RLS were insomnia, excessive daytime

sleepiness and symptoms of periodic limb movements in

sleep. Insomnia and symptoms of periodic limb movements

in sleep especially showed high odds ratios. This was not

surprising. Many studies have indicated that about 80% of

RLS sufferers have periodic limb movements in sleep [2].

More surprisingly, the multivariate logistic regression

analysis showed that gender and age group did not show

clear significant relationships with RLS. This means that

although RLS is more prevalent in females, other factors

(like having insomnia and/or periodic limb movements in

sleep) may explain the reported gender differences. We also

tested whether being treated for hypertension and heart

disease was associated with RLS, since recent studies have

reported such a relationship [8,11]. In our study, we did not

find such a relationship.

The response rate of 47% in the present study was low

and may make the data and conclusions less reliable. The

rate was, however, comparable to other epidemiological

sleep studies [15,16], and we believe that the data represent

valid estimates of RLS in the general adult population. In

these surveys, the subjects accept or reject participation

before being asked specific questions. Thus, it is unlikely

that the participants had any personal interests involved,

possibly introducing bias. One weakness with this

epidemiological study was evident concerning the question

about having worse RLS symptoms in the evening or night

than during the day. In a clinical setting, the diagnosis of

RLS can still be made in patients suffering from symptoms

throughout the day, because these patients can generally

describe an earlier phase of their disorder in which

symptoms were worse in the evening/night [14]. Although

speculative, this suggests that the overall prevalence

reported (11.5%) may actually be an underestimation of

the true rate. On the other hand, there are disorders that

mimic RLS. Fulfilling the four RLS criteria may not prove

that a subject has RLS. Thus, a possible overestimation

cannot be ruled out.

In conclusion, RLS is a frequent condition in the general

adult population, most prevalent in females. About half of

the subjects fulfilling the diagnostic criteria report

moderate to more severe symptoms. The main risk factors

of RLS are insomnia and symptoms of periodic limb

movements in sleep.

Acknowledgements

This study was supported by an unrestricted grant from

Boehringer-Ingelheim.

References

[1] Chokroverty S. Editor’s corner: restless legs syndrome, a common

disease uncommonly diagnosed. Sleep Med 2003;4(2):91–3.

[2] Allen RP, Picchietti D, Hening WA, et al. Restless legs syndrome:

diagnostic criteria, special considerations, and epidemiology. A report

from the restless legs syndrome diagnosis and epidemiology work-

shop at the National Institutes of Health. Sleep Med 2003;4(2):

101–19.

B. Bjorvatn et al. / Sleep Medicine 6 (2005) 307–312312

[3] Walters AS, LeBrocq C, Dhar A, et al. Validation of the International

Restless Legs Syndrome Study Group rating scale for restless legs

syndrome. Sleep Med 2003;4(2):121–32.

[4] Zucconi M, Ferini-Strambi L. Epidemiology and clinical findings of

restless legs syndrome. Sleep Med 2004;5(3):293–9.

[5] Salmon CT, Nichols JS. The next-birthday method of respondent

selection. Public Opin Quarterly 1983;47:270–6.

[6] Roth T, Zammit G, Kushida C, et al. A new questionnaire to detect

sleep disorders. Sleep Med 2002;3(2):99–108.

[7] Hening WA, Allen RP. Restless legs syndrome (RLS): the continuing

development of diagnostic standards and severity measures. Sleep

Med 2003;4(2):95–7.

[8] Ohayon MM, Roth T. Prevalence of restless legs syndrome and

periodic limb movement disorder in the general population.

J Psychosom Res 2002;53(1):547–54.

[9] Rijsman R, Neven AK, Graffelman W, et al. Epidemiology of restless

legs in The Netherlands. Eur J Neurol 2004;11(9):607–11.

[10] Berger K, Luedemann J, Trenkwalder C, et al. Sex and the risk of

restless legs syndrome in the general population. Arch Intern Med

2004;164(2):196–202.

[11] Ulfberg J, Nystrom B, Carter N, et al. Prevalence of restless legs

syndrome among men aged 18–64 years: an association with somatic

disease and neuropsychiatric symptoms. Mov Disord 2001;16(6):

1159–63.

[12] Rothdach AJ, Trenkwalder C, Haberstock J, et al. Prevalence and

risk factors of RLS in an elderly population: the MEMO study.

Memory and Morbidity in Augsburg Elderly. Neurology 2000;54(5):

1064–8.

[13] Nichols DA, Allen RP, Grauke JH, et al. Restless legs syndrome

symptoms in primary care: a prevalence study. Arch Intern Med 2003;

163(19):2323–9.

[14] Hening WA. Subjective and objective criteria in the

diagnosis of the restless legs syndrome. Sleep Med 2004;

5(3):285–92.

[15] Pallesen S, Nordhus IH, Nielsen GH, et al. Prevalence of

insomnia in the adult Norwegian population. Sleep 2001;24(7):

771–9.

[16] Ancoli-Israel S, Roth T. Characteristics of insomnia in the United

States: results of the 1991 National Sleep Foundation Survey. I. Sleep

1999;22(suppl 2):S347–S53.