The women who drank the most fluoridated water had boys who, by the age of three, were scoring an average of four points lower on several IQ tests. Girls were also affected, but slightly less so, with IQ scores that were three points lower than girls whose mothers had drunk less, or no, fluoridated water while pregnant.
Researchers from York University in Toronto tested fluoride levels of 512 pregnant women in six Canadian cities, 41 per cent of which had fluoridated its public water, and then tested the IQ levels of the children when they were between three and four years old.
The researchers tested levels of fluoride in the women when they were pregnant, and, not surprisingly, those who lived in fluoridated cities had higher levels of the mineral in their blood and urine—and also had children scoring lower in IQ tests.
They discovered a clear correlation between fluoride levels in the mother, and IQ scores in the child, with a 1 mg/L increase in fluoride levels in the mother's urine associated with a 4.49-point lower IQ score in boys and 3.66 lower score in girls.
Fluoride started to be added to public water in the US in the 1950s to protect children from developing bad teeth—but there have been several health alarms in recent years. The latest study isn't the first to suggest it affects IQ levels of children, and recent research has found it could damage children's kidneys and liver and disrupt thyroid function.