Restless legs syndrome status as a predictor for lower physical function

Abstract

Objective: To examine the potential long-term impact of restless legs syndrome (RLS) and other common sleep complaints on subsequent physical function (PF), we conducted a longitudinal analysis of 12,556 men in the Health Professionals Follow-up Study.

Methods: We used a set of questions recommended by the International RLS Study Group to assess RLS in 2002. We asked questions regarding other sleep complaints--insomnia, sleep fragmentation, and excessive daytime sleepiness--in 2004. We used the Physical Function (PF-10) survey of the Short Form-36 Health Survey to characterize PF in 1996 and 2008. We examined the 2008 PF-10 scores across categories of baseline RLS (2002), adjusted for age, 1996 PF-10 score, and other potential confounders.

Results: The participants with RLS at baseline had significantly lower PF-10 score 6 years later than those without RLS (mean difference = -2.32, p = 0.01), after adjusting for potential confounders. The magnitude of difference in PF-10 score for RLS symptoms ≥ 15 times/month vs no RLS was more than that of a 5-year increase of age or moderate amount of smoking. Having daily daytime sleepiness and sleep duration ≥ 9 hours/day were associated with lower mean PF value than not having these symptoms (p < 0.05 for both).

Conclusions: RLS and other sleep complaints are associated with lower PF. Our findings need to be replicated by more longitudinal studies including women and populations of other social and cultural backgrounds. It is important to understand whether RLS is an independent risk factor or a marker for other unknown risk factors for disability.

Figure 1. Mean Physical Function–10 scores in 2008 according to other sleep parameters in 2004 and sleep duration in the Health Professionals Follow-up Study

Generalized estimating equations with a multivariate regression model were used to estimate the means, adjusting for age (<60, 60–64, 65–69, 70–74, 75–79, or ≥80 years), race (Caucasian, African American, or Asian and other), smoking status (never smoker, former smoker, or current smoker: cigarettes/d, 1–14 or ≥15), alcohol drinking (g/d: 0, 0.1–9.9, 10.0–19.9, 20.0–29.9, or ≥30), body mass index (<23, 23–24.9, 25–26.9, 27–29.9, or ≥30 kg/m²), physical activity (quintiles), the Crown-Crisp phobic anxiety index (0–1, 2, 3, or >3), living status (alone or not), Physical Function (PF)–10 score in 1996, use of antidepressant drugs, history of stroke, hypertension, Parkinson disease, myocardial infarction, renal failure, erectile dysfunction, emphysema or chronic bronchitis, chronic obstructive pulmonary disease, pneumonia, asthma, pernicious anemia, or ulcerative colitis or Crohn disease (each yes/no), and use of iron-specific supplement. (A) Frequent snoring was defined as snoring every night or most nights of the week. Daily daytime sleepiness was defined if the participant answered “most of the time” to the question “How often do you get so sleepy during the day or the evening that you have to take a nap?” Insomnia was defined if the participant answered “most of the time” to 1 of the first 3 questions on sleep patterns described in Methods. (A) *Significant decrease in mean PF score to reference group (p < 0.001). (B) *Significant decrease in mean PF score to reference group of 7 hours of sleep (p < 0.01). PF = physical function.

Figure 2. Joint effects of restless legs syndrome and other sleep complaints on Physical Function–10 score in 2008

The p for interaction = 0.96. With other sleep complaints was defined if the participant answered at least half of the maximum value of the 4 sleep-related questions described in Methods. The rest of the participants were grouped under “without other sleep complaints.” Generalized estimating equations with a multivariate regression model were used to estimate the physical function (PF) means, adjusting for age (<60, 60–64, 65–69, 70–74, 75–79, or ≥80 years), race (Caucasian, African American, or Asian and other), smoking status (never smoker, former smoker, or current smoker: cigarettes/d, 1–14 or ≥15), alcohol drinking (g/d: 0, 0.1–9.9, 10.0–19.9, 20.0–29.9, or ≥30), body mass index (<23, 23–24.9, 25–26.9, 27–29.9, or ≥30 kg/m²), physical activity (quintiles), the Crown-Crisp phobic anxiety index (0–1, 2, 3, or >3), living status (alone or not), PF–10 score in 1996, use of antidepressant drugs, history of stroke, hypertension, Parkinson disease, myocardial infarction, renal failure, erectile dysfunction, emphysema or chronic bronchitis, chronic obstructive pulmonary disease, pneumonia, asthma, pernicious anemia, or ulcerative colitis or Crohn disease (each yes/no), and use of iron-specific supplement. *Significant decrease in mean PF score to reference group who had neither restless legs syndrome (RLS) nor any other sleep complaints (p < 0.05). PF = physical function.