Some studies do seem to suggest that certain vitamin deficiencies (such as Magnesium, Vitamin D, Zinc and certain Vitamin B’s) correlate with ADHD and externalising behaviour problems. Further research suggests that supplementing such deficiencies can lead to a reduction in symptoms. While not a treatment on its own, this appears to be somewhat useful as a supplement to therapy and/or medical treatment.
http://www.ncbi.nlm.nih.gov/pubmed/16846100
http://www.ncbi.nlm.nih.gov/pubmed/24610453
http://www.ncbi.nlm.nih.gov/pubmed/25373528
