Li HH, et al. - Since the serum 25-hydroxyvitamin D [25(OH)D] level in children with chronic tic disorders (CTDs) was lower than that of the healthy controls and lower serum 25(OH)D level was correlated with increased severity of the tic disorder, researchers sought to further examine this phenomenon and analyze the impact of vitamin D3 on CTDs. Participants in the study were 120 children with CTDs and 140 normal controls (mean age was 9 ± 2 years). The Yale Global Tic Severity Scale (YGTSS) and Clinical Global Impression of Severity of Illness (CGI-SI) were used to assess the tic severity, respectively. To measure serum 25(OH)D level, high-performance liquid chromatography and tandem mass spectrometry were utilized. Following supplemental vitamin D3 treatment, serum 25(OH)D level and scores of YGTSS total, motor tics, phonic tics, total tic, impairment, and CGI-SI improved significantly in children with CTDs without adverse reactions. Because of its low cost and excellent safety, vitamin D3 supplementation can be an effective way to improve symptoms in some children with CTDs.