Skip to main content
Toggle Menu of ADA WebSites
ADA Websites
Toggle Search Area
Toggle Menu
e-mail Print Share

New Zealand study finds no correlation between fluoridated water and lower IQs

May 27, 2014
New research from the University of Otago’s Dunedin Multidisciplinary Study does not support claims that fluoridating water adversely affects children’s mental development and adult intelligence quotient.

The Dunedin Study has followed nearly all aspects of the health and development of about 1,000 people born in Dunedin in 1972 and 1973 up to age 38. 

In the study published online May 15 in the American Journal of Public Health, researchers examined the theory that exposure to levels of fluoride used in community water fluoridation is toxic to the developing brain and can cause IQ deficits. 

Lead author Dr. Jonathan Broadbent says the new research focused on study members’ fluoride exposure during the first five years of their lives, a critical period in brain development, after which IQ is known to be relatively stable.

Researchers compared the IQs of study members who grew up in Dunedin suburbs with and without fluoridated water, and they factored for use of fluoride toothpaste and tablets.

They examined average IQ scores between the ages of 7-13 years and at age 38, as well as subtest scores for verbal comprehension, perceptual reasoning, working memory and processing speed. Data on IQ were available for 992 and 942 study members in childhood and adulthood, respectively.

Dr. Broadbent says the team controlled for childhood factors associated with IQ variation, such as socio-economic status of parents, birth weight and breastfeeding, and secondary and tertiary educational achievement, which is associated with adult IQ.

“Our analysis showed no significant differences in IQ by fluoride exposure, even before controlling for the other factors that might influence scores. In line with other studies, we found breastfeeding was associated with higher child IQ, and this was regardless of whether children grew up in fluoridated or non-fluoridated areas.

“Our findings will hopefully help to put another nail in the coffin of the complete canard that fluoridating water is somehow harmful to children’s development,”Dr. Broadbent added. “In reality, the total opposite is true, as it helps reduce the tooth decay blighting the childhood of far too many New Zealanders.”

See the article online at