Twenty-seven studies were included in the meta-analysis with sample sizes that ranged from 60 to 956 children.
Fluoride exposure reduced intelligence test scores in the meta-analysis (SMD -0.45, 95% CI -0.56 to -0.34; Ι²=80%). The effect was slightly smaller in studies reporting only CRT-RC scores (SMD -0.36, 95% CI -0.48 to -0.25; Ι²=78%; 16 studies) and in studies of drinking water fluoride exposure only (SMD -0.29, 95% CI -0.44 to -0.14; Ι²=82%; nine studies). More recently published studies gave smaller effect sizes (SMD 0.02 per year, 95% CI 0.006 to 0.03), but child age had no impact on the results.
Fluoride exposure increased the risk of low or marginal CRT-RC scores (RR 1.93, 95% CI 1.46 to 2.55; Ι²=59%; 16 studies); results were similar for studies that included only drinking water fluoride exposure (RR 1.75, 95% CI 1.16 to 2.65; Ι²=71%; nine studies).
There was no evidence of publication bias.