Meta-analysis of attention-deficit/hyperactivity disorder or attention-deficit/hyperactivity disorder symptoms, restriction diet, and synthetic food color additives

Abstract

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.

FIGURE 1

Restriction dietary crossover studies: homogenous results. The size of the square indicates the study weight, and the width of the diamond is the 95% confidence interval (CI).

FIGURE 2

Food colors results for parent report: all studies, teacher/observer reports of high quality studies, and psychometric tests of attention. The size of the square indicates the study weight, the line for individual studies indicates the 95% confidence interval (CI). The summary effects are shown for parent, teacher/observer, and test results by the diamond; the center of the diamond is the effect size and the width of the diamond is the 95% confidence interval. Comparison across studies using the graph metrics can only be done within domain.