Introduction - Investigation of seasonal differences in serum 25-hydroxy vitamin D (25(OH)D) in Scottish resident children with epilepsy(CWE) on antiepileptic drugs(AEDs)> 1year compared to those without epilepsy.

Method - CWE were enrolled via Royal Hospital for Sick Children(RHSC), Edinburgh, epilepsy clinics. Controls were from previously healthy children attending RHSC's outpatient/emergency departments. At enrollment, volunteers completed standardised questionnaires on bone pain, quality of life, diet, clinical and demographic details, had 25(OH)D, parathyroid hormone, bone profile, liver assays taken. Volunteers were invited for reassessment six months post-baseline. If children did not return, additional children were recruited aiming to achieve case:control of 1:1. 25(OH)D levels (nmol/l) were considered: Deficient <25; Insufficient 25-49; Sufficient >50.

Results - 25 CWE enrolled; all had reassessments. 35 controls enrolled; 6 had summer and winter assessments, 19 winter only, 10 summer only. In winter, 13(52%) CWE were deficient, 7(28%) insufficient compared to 10(40%) controls who were deficient, 8(32%) insufficient. In summer, 2(8%) CWE were deficient, 11(44%) were insufficient vs zero(0%) controls deficient and 4(25%) insufficient.

Conclusion - A high proportion of Scottish children are generally deficient/insufficient in 25(OH)D in winter. Most children without epilepsy have sufficient levels over the summertime whereas a substantial propoprtion of CWE on AED's continue to have deficient/insufficient 25(OH)D. Consideration should be given to provide year-long vitamin D supplementation in all children on AED's and to all Scottish children during wintertime.