Till C, Green R, Flora D, Hornung R, Martinez-Mier EA, Blazer M, Farmus L, Ayotte P, Muckle G, Lanphear BP. Environment International. 2020 Jan;134:105315. doi: 10.1016/j.envint.2019.105315
Fluoride is a mineral that can occur naturally in air, soil, and water. In some regions, it is added to drinking water to prevent tooth decay. About one-third of Canadians have fluoride added to their public water supply. Infants can be exposed to fluoride when fluoridated water is used to make formula. Some concerns have been raised that mother’s exposure to fluoride during pregnancy may affect a child’s intellectual function (their ability to reason, plan, think, and communicate).
The goal of this MIREC Biobank study was to see if there is an association between infant’s exposure to fluoride from formula and child IQ at around 3 years of age.
The researchers studied 398 mother-child pairs from the MIREC study who reported drinking tap water. About half of the children in the study were exclusively breastfed during the first six months of life, and the other half had formula introduced during their first six months. The researchers estimated the amount of fluoride in the drinking water at the families’ homes based on data from the city’s water systems. At around age 3 years, the child’s IQ was tested.
Thirty-eight percent of the MIREC mother-child pairs lived in communities which added fluoride to the drinking water. The researchers found that an increase of 0.5 mg/L in water fluoride concentration (approximately equal to the difference between fluoridated and non-fluoridated water) was associated with about a 9-point decrease in Performance IQ among formula-fed children and a 6-point decrease in breast-fed children. A child’s IQ score can be divided into Verbal IQ and Performance IQ. Performance IQ is a measure of visual-motor coordination skills and the ability to reason with visual information, such as puzzles and shapes.
One of the limitations of this study is that the researchers didn’t have any information on the level of fluoride in the infant formulas consumed in this study. They also didn’t know if the formula was mixed with tap water or bottled water, so there is uncertainty about how much fluoride the children were exposed to.
In conclusion, this study suggested that children who were exposed to higher levels of fluoride in tap water also had lower performance IQ scores and the association was stronger if the children were fed formula as infants. As there is limited benefit from fluoride consumption in the first six months of life, the researchers suggest that fluoride exposure be limited during that period by using non-fluoridated water or water with lower fluoride content when mixing with formula. Breastmilk contains very low levels of fluoride.