Abstract
We examined seasonal and geographic effects on vitamin D [25(OH)D] levels, association with attention-deficit/hyperactivity disorder (ADHD) symptom severity, and effects of supplementation in 222 children age 7–10 with rigorously diagnosed ADHD. 25(OH)D insufficiency rates were 47.2 % in Ohio and 28.5 % 400 miles south in North Carolina. Nadir of 25(OH)D levels was reached by November in Ohio, not until January in NC. Thirty-eight children with insufficiency/deficiency took vitamin D (1000–2000 IU/day for a month); levels rose 52 %. Although inattention did not correlate with 25(OH)D at screen nor improve significantly with supplementation, inattention improvement after supplementation correlated with 25(OH)D increase (rho = 0.41, p = 0.012). A clinically significant proportion of children with ADHD have insufficient 25(OH)D even at summer's end, more so in the winter and north of the 37th parallel. The significant correlation of inattention improvement with 25(OH)D increase suggests further research on 25(OH)D as ADHD treatment.