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Meta-Analysis of Attention-Deficit/Hyperactivity Disorder or Attention-Deficit/Hyperactivity Disorder Symptoms, Restriction Diet, and Synthetic Food Color Additives

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Objective

The role of diet and of food colors in attention-deficit/hyperactivity disorder (ADHD) or its symptoms warrants updated quantitative meta-analysis, in light of recent divergent policy in Europe and the United States.

Method

Studies were identified through a literature search using the PubMed, Cochrane Library, and PsycNET databases through February 2011. Twenty-four publications met inclusion criteria for synthetic food colors; 10 additional studies informed analysis of dietary restriction. A random-effects meta-analytic model generated summary effect sizes.

Results

Restriction diets reduced ADHD symptoms at an effect of g = 0.29 (95% CI, 0.07–0.53). For food colors, parent reports yielded an effect size of g = 0.18 (95% CI, 0.08–0.24; p = .0007), which decreased to 0.12 (95% CI, 0.01–0.23; p < .05) after adjustment for possible publication bias. The effect was reliable in studies restricted to food color additives (g = 0.21, 95% CI = 0.06–0.36) but did not survive correction for possible publication bias and was not reliable in studies confined to Food and Drug Administration–approved food colors. Teacher/observer reports yielded a nonsignificant effect of 0.07 (95% CI = −0.03 to 0.18; p = .14). However, high-quality studies confined to color additives yielded a reliable effect (g = 0.22, 95% CI = 0.10–0.41, p = .030) that survived correction. In psychometric tests of attention, the summary effect size was 0.27 (95% CI = 0.07–0.47; p = .007) and survived correction. An estimated 8% of children with ADHD may have symptoms related to synthetic food colors.

Conclusions

A restriction diet benefits some children with ADHD. Effects of food colors were notable were but susceptible to publication bias or were derived from small, nongeneralizable samples. Renewed investigation of diet and ADHD is warranted.

Section snippets

Method

Studies were identified through a literature search using the PubMed, Cochrane Library, and PsycNET electronic databases. We initially used the following combination of terms: behavior or ADHD or hyperactivity or impulsivity and food coloring; behavior or ADHD or hyperactivity or impulsivity and diet; behavior or ADHD or hyperactivity or impulsivity; and the name of each individual food coloring by either its formal or generic name (listed in parenthetical statement earlier), as well as the

Open-Label Trials

Before evaluating the effects of food colors, we examined the evidence regarding dietary restriction, in which synthetic food colors and/or other additives were eliminated as a component of the restrictive diet and ADHD symptoms were evaluated. Our literature review identified 14 open-label trials of hyperactive children that offered an operational definition of a “responder” (e.g., 25% improvement in symptoms), with aggregated N = 2025.20, 24, 26, 27, 28, 29, 30, 31, 32, 33, 34 (Note that

Discussion

The relation of food color additives to ADHD has provoked periodic controversy for nearly 40 years, but has gained renewed currency with review by European and American authorities recently taking different policy actions. The present meta-analysis provides new clarification and nuance, and overturns some previous conclusions. It is important to note that we emphasized randomized controlled trials, because these provide prima facia evaluation of causality. We began by examining whether a

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    This study was supported by the North American Branch of the International Life Sciences Institute (ILSI) Technical Committee on Food and Chemical Safety. ILSI North America is a public, nonprofit foundation that provides a forum to advance understanding of scientific issues related to the nutritional quality and safety of the food supply by sponsoring research programs, educational seminars and workshops, and publications. ILSI North America receives support primarily from its industry membership. The Life Sciences Research Organization Inc and Dr. Nigg received a grant from the organization for their work reviewing, analyzing, and summarizing the information contained in this article. Partial funding for this project was also received from the National Confectioners Association.

    The opinions and conclusions expressed herein are those of the authors and do not necessarily represent the views of either funding organization.

    Disclosure: Drs. Falk and Lewis are employees of the Life Sciences Research Organization, Inc. (LSRO). LSRO has received research support from numerous federal government agencies (including the U.S. Food and Drug Administration), trade associations, and corporations (including food and dietary supplement manufacturers and distributers). Drs. Nigg, Lewis, Edinger, and Falk report no biomedical financial interests or potential conflicts of interest.

    Supplemental material cited in this article is available online.

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