66. Association Between Maternal Fluoride Exposure During Pregnancy and IQ Scores in Offspring in Canada (lay summary)

Green R, Lanphear BP, Hornung R, Flora D, Martinez-Mier EA, Neufeld R, Ayotte P, Muckle G, Till C. Journal of the American Medical Association Pediatrics. 2019 Aug 19. doi: 10.1001/jamapediatrics.2019.1729

Fluoride is a mineral found naturally in most water sources. At low concentrations, fluoride in drinking water prevents cavities and improves oral health. About one-third of Canadians have fluoride added to their public water supply to protect teeth from decay.

Some groups have raised concerns that fluoride intake during pregnancy may affect child intellectual function (ability to reason, plan, think, and communicate).  The purpose of this MIREC Biobank study was to examine the association between prenatal exposure to fluoride and child IQ.

In this study, urine from each trimester of pregnancy was analysed for fluoride.  During pregnancy, the women were asked how much water they drank, including tea and coffee.  At around 3 years of age, the child’s IQ was measured as part of the MIREC-CD Plus study.  Data on prenatal exposure to fluoride and child IQ were available for 512 mother-child pairs.  In MIREC-CD Plus, about half (41%) of participants lived in communities where fluoride was added to the tap water (Toronto, Hamilton, and Halifax); while 59% lived in communities that do not add fluoride to tap water (Vancouver, Montreal and Kingston).

The researchers found that women who lived in cities with fluoridated water had fluoride levels in their urine that were two times higher than for women who lived in communities without fluoridated water.  Higher levels of fluoride in mother’s urine were associated with lower IQ scores in boys but not girls.  This association held up after accounting for maternal education, quality of home environment, city, and other characteristics of the study population. When the researchers estimated fluoride intake per day from all beverages, they found an association between higher intake of fluoride and lower IQ score in boys and girls.

This study is one of the few that has examined prenatal exposure to fluoride and child IQ.  The results suggest that exposure to fluoride during pregnancy may be associated with lower scores on IQ tests for 3-4 year olds.  The authors conclude that these findings indicate the possible need to reduce fluoride intake during pregnancy.  Further research on fluoride exposure and child IQ is planned.