To contrast vitamin D25-OH levels among MTHFR C677T genotypes in children with ADHD.

Vitamin D deficiency in ADHD patients has been well documented in the literature, but there is no consensus as to the explanation for this association. There has also been conflicting evidence regarding the association between MTHFR C677T gene status and ADHD. Given recent reports of a correlation between low MTHFR C677T prevalence and regions with high ultraviolet radiation (UVR), we sought to examine MTHFR status and vitamin D25-OH levels, which themselves are directly influenced by UVR exposure. 

Serum vitamin D25-OH levels and MTHFR C677T genotype (wild type (CC), heterozygous (CT), and homozygous (TT) polymorphisms) were determined for 50 children with ADHD.  ANOVA was used to contrast vitamin D25-OH levels among MTHFR C677T genotypes.

Serum vitamin D25-OH differed significantly among the three genotypes [F_2,42 = 5.02; p=0.01; n= (CC 18; CT 21; TT 11)]. The CC variant had lower vitamin D levels than the TT variant, and the CT variant had intermediate levels that did not differ from the other two genotypes.

Existing literature does not suggest a genetic predilection for vitamin D deficiency in children with ADHD. However, an interaction between folate and vitamin D levels regulated by UVR intensity as a mechanism that preserves both nutrients has been suggested. The TT variant of MTHFR is thermolabile and unable to process folic acid efficiently at high UVR exposure, which is typically necessary for vitamin D formation.  As such, individuals with MTHFR TT may manufacture and/or maintain vitamin D more efficiently due to their genetic need to avoid prolonged UVR exposure.  Hence, vitamin D levels may be higher at baseline in children with MTHFR TT status. In either case, our findings suggest a possible yet unelucidated interaction between MTHFR C677T status and vitamin D and children with ADHD.