BACKGROUND: Restless legs syndrome (RLS) and attention-deficit hyperactivity disorder (ADHD) are disorders with virtually unknown etiologies. Several studies suggest that these disorders are comorbid. However, previous findings may have been influenced by study participants undergoing medical treatments. Thus, the association between RLS and ADHD needs to be investigated in a large population of individuals, not in continuous medical treatment.
MATERIALS AND METHODS: This was a cross-sectional study of 25,336 participants enrolled in the Danish Blood Donor Study from May 1, 2015, to February 1, 2017. Study participants completed the Cambridge-Hopkins RLS questionnaire, reported experience of involuntary leg movements during sleep (ILMS), completed the Adult ADHD Self-Report Scale v.1.1 (ASRS), and provided information on sex, age, body mass index, smoking status, alcohol consumption, whole blood donation history, and self-appraised quality of sleep. Associations between RLS and ADHD symptoms, including subtypes, were examined using multivariate linear- and logistic regression analyses.
RESULTS: Of the 25,336 participants with complete data, 1,322 (5.2%) were classified with RLS, and 653 (2.6%) experienced ADHD symptoms. RLS sufferers were more prone to classify with ADHD according to the full ASRS (OR = 3.57, 95% CI: 3.14-4.0), and they were also more likely to experience ADHD-subtype symptoms (inattention, OR = 1.66, 95% CI: 1.43-1.90; hyperactivity-impulsivity, OR = 1.90, 95% CI: 1.66-2.14). Finally, RLS sufferers with ILMS had increased odds for ADHD symptoms compared with RLS sufferers without (OR = 2.15, 95% CI: 1.30-3.55). This was also observed for the hyperactivity-impulsivity subtype (OR = 5.57, 95% CI: 2.14-14.5).
CONCLUSIONS: RLS and ADHD are associated and may be comorbid disorders.