Context Attention deficit/hyperactivity disorder (ADHD) is a neurological disorder associated with iron dysregulation in children. Although previous focus was on examining systemic iron status, brain iron content may be a more reliable biomarker of the disorder. Objective This systematic review examines whether children with ADHD have lower serum as well as brain iron concentrations, compared with healthy control subjects (HCS). Data sources A systematic literature search was conducted in Medline via PubMed, the Cochrane Library, Web of Science, Embase. and Ovid for papers published between 2000 and June 7, 2019. Data extraction Studies were included if the mean difference of iron concentration, measured as serum iron, serum ferritin, or brain iron, between children with ADHD and HCS was an outcome measure. Data analysis Preferred Reporting Items for Systematic Reviews and Meta-Analyses guidelines were followed. Risks of bias within and between studies were assessed using the quality assessment tools of the National Institutes of Health. Of 599 records screened, 20 case-control studies met the inclusion criteria. In 10 of 18 studies in which serum ferritin concentration was assessed, and 2 of 10 studies that assessed serum iron, a significant difference between children with ADHD and HCS was observed. Results of systemic iron levels were inconsistent. In 3 studies in which brain iron concentration was assessed, a statistically significant, lower thalamic iron concentration was found in children with ADHD than in HCS. Conclusion The evidence, though limited, reveals that brain iron rather than systemic iron levels may be more associated with the pathophysiology of ADHD in children. Larger, longitudinal, magnetic resonance imaging studies are needed to examine any correlations of iron deficiency in specific brain regions and symptoms of ADHD.

Recent evidence suggests that vegetarian and vegan diets may increase the risk and symptoms of depression, a mental health condition affecting 350 million people globally. We aimed to systematically review the literature on the associations between vegetarian and/or vegan diets and the risk or symptoms of depression using evidence from both observational and intervention studies. We followed the Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines, with pre-specification of all methods. A systematic search for relevant papers was performed on Medline and Embase, Web of Science and the Cochrane Library for cohort, case-control, cross-sectional studies or randomised controlled trials examining associations between a vegetarian or vegan diet and depression in adults. Three independent reviewers extracted data and assessed risk of bias using the National Heart, Lung, and Blood Institute of the National Institutes of Health for Quality Assessment of Observational Cohort and Cross-Sectional Studies and Controlled Studies. Evidence was tabulated according to the type of diet analysed as vegetarian, vegan or both and narratively synthesised. A total of 23 studies (18 cross-sectional, three prospective cohort and two randomised controlled trials) with 25 study outcomes were eligible for inclusion in this review. Conflicting evidence was found on the association between vegetarian or vegan diets and depression. Eleven (44%) of the outcomes indicated that vegetarian and vegan diets were associated with higher rates of depression, while seven (28%) outcomes revealed beneficial effects of the diets on depression. Seven (28%) outcomes found no association between vegetarian and vegan diets and depression, although two of these studies found a higher risk of depression in some groups. The quality of evidence was rated as good for four of the studies with the remaining 19 studies rated as fair. The evidence on the effect of vegetarian and vegan diets on depression is contradictory, possibly due to the heterogeneity of the studies analysed. Further research, including longitudinal and intervention studies, is required to resolve this observation.

Depression is a mental health condition, affecting 350 million people globally (1). Recent evidence has found diet to be a novel approach to reduce depressive symptoms (2). This study aimed to systematically review the literature on the associations between vegetarian and/or vegan diets and the risk or symptoms of depression and compare these with that of omnivorous diets. A systematic search for relevant papers in Medline via PubMed, EMBASE, Web of Science and Cochrane Library databases was implemented using the following Medical Subject Heading (MeSH) and free text terms: "depression" or "depressive disorder" or "depressive disorder, major" or "postpartum depression" or "bipolar depression" and "vegetarian" or "vegetarian diet" or "vegetarianism" or "vegan" or "vegan diet" or "veganism". Studies were included if they examined the association between vegetarian/vegan diets and depression or depressive symptoms in individuals aged 18 or older. Cohort, cross-sectional, and case-control studies, as well as randomized controlled trials (RCT), published from January 1 st , 2000 to May 31, 2019, were explored. Studies not published in English; investigating lifestyle patterns or other diets rich in fruits and vegetables but not vegetarian/vegan diets specifically; examining individual dietary nutrients or components rather than diet as a whole; investigating quality of life rather than depression specifically; investigating mental health disorders other than depression; animal studies; systematic reviews; meta-analyses; intervention studies that are not RCTs; conference abstracts; case reports; surveys or letters, were excluded. The systematic review followed Preferred Reporting Items for Systematic Reviews and Meta-Analyses (PRISMA) guidelines. Risks of bias within and between studies were assessed using the quality assessment tools of the National Heart, Lung and Blood Institute of the National Institutes of Health for Case-Control Studies and for Observational Cohort and Cross-Sectional Studies. Out of 861 articles screened, 19 studies met the inclusion criteria. Fifteen of these studies looked at vegetarian diets specifically, 2 looked at vegan diets specifically, and the remaining 2 looked at both vegetarian and vegan diets. Of the 17 studies investigating associations between vegetarian diets and depression, 5 found vegetarian diets to lower rates of depression, 10 studies found it to increase depression/depressive symptoms, and the remaining 2 found no association. Of the 4 studies investigating associations between vegan diets and depression, 2 studies found the diet to be beneficial against depression, whilst the other 2 found it to increase depression. Overall, the findings revealed conflicting evidence on the association between vegetarian/vegan diets and depression. Due to the heterogeneity of these data, meta-analyses were not performed. Conflicting evidence was revealed in this systematic review: some studies suggested vegetarian diets had higher rates of depression, whereas others suggested this dietary...

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