Fluoride exposure inversely associated with children’s IQ

A recent study links increased fluoride exposure to lower IQ in a dose-response fashion among children.

Researchers performed a systematic review and meta-analysis. They searched multiple online databases for epidemiological studies in which children’s IQ scores were examined in relation to prenatal or postnatal fluoride exposure.

A total of 74 studies, of which 64 were cross-sectional and 10 were cohort, met the eligibility criteria and were included in the meta-analysis. Most of the studies were conducted in China (n=45), while others were conducted in Canada (n=3), Denmark (n=1), India (n=12), Iran (n=4), Mexico (n=4), New Zealand (n=1), Pakistan (n=2), Spain (n=1), and Taiwan (n=1). Risk of bias was high in 52 studies and low in 22.

Of the studies, 64 showed inverse associations between fluoride exposure measures and children’s IQ. Pooled data from 59 studies with group-level measurements of fluoride in drinking water, dental fluorosis, or other measures of fluoride exposure (47 high risk of bias, 12 low risk of bias; n=20,932) indicated that fluoride exposure was associated with decreased IQ scores (pooled standardized mean difference [SMD], −0.45, 95 percent confidence interval [CI], −0.57 to −0.33; p<0.001).

Pooled data from 31 studies in which fluoride was measured in drinking water, a dose-response association was seen between fluoride exposure and IQ (SMD, −0.15, 95 percent CI, −0.20 to −0.11; p<0.001). This association remained when fluoride exposure was limited to <4 mg/L and <2 mg/L but disappeared when exposure was limited to <1.5 mg/L.

Pooled data from studies with low risk of bias showed an inverse association across fluoride exposures of <4, <2, and <1.5 mg/L in drinking water.

In 20 studies in which fluoride was measured in urine, an inverse dose-response association was also observed (SMD, −0.15, 95 percent CI, −0.23 to −0.07; p<0.001). This remained true across exposures of <4-, <2-, and <1.5-mg/L fluoride and in analysis restricted to studies with low risk of bias.

Finally, in 13 studies with individual-level measures, each 1-mg/L increase in urinary fluoride was associated with a decrease of 1.63 points in IQ score (95 percent CI, −2.33 to −0.93; p<0.001). This association held true when analysis was restricted to studies with low risk of bias (–1.14 points, 95 percent CI, –1.68 to –0.61; p<0.001).