Dietary patterns and attention deficit/hyperactivity disorder (ADHD): A systematic review and meta-analysis

Background: The Attention Deficit Hyperactivity Disorder (ADHD) is a neurobiological disorder characterized by persistent symptoms of inattention, impulsivity and hyperactivity. The diet during childhood has been investigated as a factor potentially involved in the ADHD etiology. Objective: To review systematically the evidence of the association between dietary patterns and ADHD. Methods: Two independent literature searches were carried out in PubMed, LILACS and PsycINFO databases. The studies included were only those that assessed dietary patterns and ADHD in children and adolescents. Due to heterogeneity between the studies random-effects models were used to pool the estimates. Results: We included fourteen observational studies (four cohorts, five case-control and five cross-sectional studies). In the pooled analysis, healthy dietary patterns were protective against ADHD (OR: 0.65; 95% CI: 044-0.97), while unhealthy dietary patterns were found as risk to ADHD (OR: 1.41; 95% CI: 1.15-1.74). After stratifying the studies by design (cohort/case control or cross-sectional), continent (Europe or Asia/Oceania) and sample size (>= 1000 or < 1000) the effects remained. Limitations: Absence of randomized controlled trials at the literature on this subject and scarce evidence from more robust designs, such as cohort and case-control studies. Conclusion: This study suggests that a diet high in refined sugar and saturated fat can increase the risk, whereas a healthy diet, characterized by high consumption of fruits and vegetables, would protect against ADHD or hyperactivity. Nevertheless, giving the number and the design of most of the studies available in the literature, the current evidence is weak. More studies using longitudinal design need to be performed to reinforce this evidence.