Hypovitaminosis-D has been linked to neuropsychiatric conditions, but little is known about vitamin D status in individuals with chronic tic disorders (CTD). This study sought to determine whether vitamin D levels are associated with the severity of tics and presence and severity of comorbid obsessive-compulsive disorder (OCD) and/or attention-deficit/hyperactivity disorder (ADHD). Methods: This is a cross-sectional sub-study of the European Multicentre Tics in Children Studies (EMTICS).

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... D [25(OH)D] levels (ng/ml) were obtained for 327 participants with CTD at study entry and tic severity was measured using the Yale Global Tic Severity Scale (YGTSS). An association between tic severity and presence and severity of comorbid OCD and/or ADHD symptoms was analysed using multilevel models controlling for season, site, sex, age and presence of comorbid OCD and/or ADHD. Results: The participants comprised 247 boys and 80 girls (4-16 years, mean [SD], 10.9 [2.72]). Hypovitaminosis-D ([25(OH)D] < 20ng/ml) was present in 33% of participants with CTD and/ or comorbid OCD and/ or ADHD. The authors found no association between 25(OH)D levels and tic severity or OCD symptom severity. However, lower 25(OH)D levels were significantly associated with increased severity of ADHD symptoms in participants with CTD (β = -0.25, s.e. = 0.08, 95% CI, -0.42 to -0.09; p < 0.01). Conclusion: Additional research is needed to confirm these findings and assess whether hypovitaminosis-D may represent an underlying biological vulnerability for comorbid ADHD symptoms in CTD as it may signpost novel strategies for prevention and treatment.