Comparing Fluoride Exposures in Pregnant Canadian Women: Fluoridated versus Nonfluoridated Drinking Water

Fluoridated water is piped to more than one-third of the Canadians and nearly three-quarters of the Americans who use public water systems. Although fluoride helps prevent dental cavities, some studies have suggested that higher prenatal exposures may affect neurodevelopment.34 Those findings make it important to understand exposure levels in general populations. Research published in Environmental Health Perspectives now sheds light on fluoride levels in pregnant women in Canada. As part of the Maternal–Infant Research on Environmental Chemicals (MIREC) Study, researchers measured urinary fluoride concentrations in 1,566 pregnant women from 10 Canadian cities. Seven of the cities add fluoride to public drinking water, while three don’t. After adjusting for urine dilution and potential confounders— including maternal age, pre-pregnancy body mass index, smoking status, water and tea consumption, education, and income—mean fluoride concentrations were found to be about twice as high in the urine of women living in cities with fluoridated water, compared with the urine of women in cities with nonfluoridated water. The study also found that, among all the mothers, average fluoride concentrations increased between the first and third trimesters. The authors speculated that this increase may be due to increased fluoride uptake by the fetus earlier in pregnancy, when bone tissue is forming. This study offers important insight into previous studies linking adverse neurodevelopmental outcomes to relatively high fluoride exposures. A 2012meta-analysis of 27 studies conductedmostly in China reported an association between higher fluoride exposure and lower IQ scores in children. None of the studies reported water fluoride levels at or below the “optimal” concentration of 0:7 mg=L recommended by Health Canada and the U.S. Public Health Service. Concentrations in nearly half the studies were within the maximum contaminant level goal (MCLG) of 4 mg=L, which the U.S. Environmental Protection Agency (EPA) set as the maximum amount of fluoride allowed in drinking water. Far fewer levels were within the Canadian version of the MCLG, known as themaximum acceptable concentration, which is set at 1:5 mg=L. “It’s often stated that [the 2012 meta-analysis] is not applicable to North America because the studies included were based on areas with endemic fluorosis, meaning that the drinking water in