A new study adds to rising concerns about the impact of fluoride in drinking water. Researchers found a link between higher levels of fluoride exposure and lower IQ scores in children, restarting the debate over the safety of fluoride in public water supplies.

The latest study, published in JAMA Pediatrics, reviewed 74 studies across 10 countries, on the effects of fluoride in water on children's IQ levels and found a statistically significant link between higher fluoride exposure and lower IQ scores in children.

Researchers at the government's National Toxicology Program who conducted the study noted that even a slight increase in fluoride levels in urine—such as an increase of 1 mg/L—was associated with a 1.63-point decrease in IQ. Measuring fluoride in urine helps assess total fluoride intake.

"This systematic review and meta-analysis found inverse associations and a dose-response association between fluoride measurements in urine and drinking water and children's IQ across the large multi-country epidemiological literature," the researchers wrote.

Even though the decrease in cognitive health may seem slight, the impact is significant on a wider scale, the researchers noted. "A 5-point decrease in a population's IQ would nearly double the number of people classified as intellectually disabled," they wrote.

However, the researchers do not recommend removing fluoride from drinking water based on their findings. Most of the 74 studies reviewed were of low quality and were conducted in countries outside the United States, such as China. Additionally, there was limited data and uncertainty regarding the dose-response relationship between fluoride exposure and children's IQ when fluoride exposure was measured solely through drinking water at concentrations below 1.5 mg/L.

"To our knowledge, no studies of fluoride exposure and children's IQ have been performed in the United States, and no nationally representative urinary fluoride levels are available, hindering application of these findings to the US population. Although this meta-analysis was not designed to address the broader public health implications of water fluoridation in the United States, these results may inform future public health risk-benefit assessments of fluoride," the researchers wrote.

The U.S. recommends a fluoride concentration of 0.7 mg/L in drinking water, which is considered a safe and effective level for preventing tooth decay.

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