"ADHD [attention-deficit hyperactivity disorder] patients were overrepresented in the group with low levels of some vitamins, possibly indicative of inadequate dietary intake of these micronutrients in a subgroup of patients. It is important to identify these patients in dietary intervention trials of ADHD."
So said the study findings reported by Elisabeth Toverud Landaas and colleagues  (open-access) providing some potentially important data on how nutritional factors might intersect with the diagnosis of ADHD. So: "Owing to the important and neurologically relevant functions of vitamins and the lack of studies exploring this topic in ADHD, we measured serum levels of the major vitamin classes in a sample of adult ADHD patients and controls to determine whether vitamin levels are associated with ADHD diagnosis and psychiatric symptoms." Said participants (n=133) were young adults and most were listed as having ADHD according to a "Norwegian national registry of adult ADHD patients." Vitamin levels were assessed from blood samples and compared with results for 131 control participants as per other studies on this cohort from this authorship group . It's worth pointing out that samples were in deep freeze storage for between 2-9 years between collection and thawing for analysis.
Various vitamins were measured in those samples (vitamins A, B6, , B9, B12 and D to name a few) alongside levels of cotinine "to assess [tobacco] smoking status." The analytical assay(s) of choice was, in the most part, a familiar one to this blog: liquid- or gas chromatography-tandem mass spectrometry.
Results: "The concentrations of vitamins B2, B6 and B9 were all significantly lower in the ADHD group." When results were analysed according to percentiles based on blood levels of the various vitamins results similarly showed that those with ADHD were 'over-represented' in the lower levels bandings of those previously described vitamins. Smokers, as defined by a "widely used cut-off of 80 nmol/L" of blood cotinine, were also over-represented in the ADHD group (66%) compared with control participants' samples (12%). The authors reported that: "vitamin B6 and B9 levels were significantly higher in non-smoking ADHD patients compared with smokers" suggesting that lifestyle choices may play a role in some of the results obtained. Finally, when it came to looking at any possible association(s) between measured vitamin levels and behaviours pertinent to ADHD (derived from responses to the Adult ADHD Self-report Scale (ASRS), the authors report some preliminary observations but I'd like to see a little more data before anything further is made of this.
These are interesting results (aren't they always!). I note that the authors make reference to the findings reported by Julia Rucklidge and colleagues on a vitamin-mineral mix for ADHD (see here) and the idea that correcting vitamin deficiencies might have effects beyond just the somatic. There are however caveats to the latest results: "The reason why we observed association between lower levels of some vitamins and ADHD is uncertain and probably multifactorial. Regrettably, we do not have information on lifestyle and nutrient intake from the participants to help in the interpretation of our observations. It is reasonable to think that differences in dietary factors may partly be responsible for the differences." Indeed.
There is also one final observation to touch upon in the Landaas results concerning the vitamin/hormone of the hour: vitamin D. Although there was no overall difference in vitamin D concentrations in the ADHD and not-ADHD group samples, the authors did observe that: "for vitamin D, ADHD patients were significantly overrepresented both in the lowest and highest 10th percentile groups." Bearing in mind past research has suggested that ADHD might be yet another diagnosis/label where vitamin D deficiency might be a feature (see here) it is pertinent that the authors suggest: "One reason for the overabundance of ADHD patients in the highest 10th percentiles of vitamin D may thus be that relatively more ADHD patients take vitamin D supplements, either as part of an experimental treatment of symptoms or as a consequence of a diagnosed vitamin D deficiency."
Finally: "It is possible that low levels of certain vitamins may contribute to ADHD symptoms. Dietary intervention trials have shown promising effects in ADHD. Thus, identification and correction of low vitamin levels could be beneficial in treatment of ADHD. Further studies are warranted for replication and for examination of the underlying mechanisms."
 Landaas ET. et al. Vitamin levels in adults with ADHD. BJPsych Open. 2016 Dec 13;2(6):377-384.
 Aarsland TI. et al. Serum concentrations of kynurenines in adult patients with attention-deficit hyperactivity disorder (ADHD): a case-control study. Behav Brain Funct. 2015 Nov 5;11(1):36.
Landaas ET, Aarsland TI, Ulvik A, Halmøy A, Ueland PM, & Haavik J (2016). Vitamin levels in adults with ADHD. BJPsych open, 2 (6), 377-384 PMID: 27990293