The analysis, published in JAMA Pediatrics on Jan. 6, found that fluoride exposure exceeding 1.5 milligrams per liter (mg/L) was associated with reduced intelligence in children. The studies reviewed in the analysis measured fluoride levels in both drinking water and urine, with urinary fluoride serving as a proxy for total fluoride exposure. Among the 74 reviewed studies, 64 found that higher levels of fluoride exposure were linked to lower IQ scores in children. The strength of this association is considered moderate to large. Thirty-one studies reviewed noticed a dose-response, such that increased fluoride levels in drinking water were linked to further decreases in children's IQ results.