Second Opinion: A look at the recent fluoride and IQ study

2016 10 12 14 41 06 881 Dr B Second Opinion 400

A study published in JAMA Pediatrics on August 19 has reported an association between fluoride exposure during pregnancy and IQ scores of Canadian children. Researchers measured fluoride exposure for 512 Canadian mothers through urine samples collected during each trimester of their pregnancy. About 40% of the mothers lived in fluoridated communities, and the remaining 60% lived in nonfluoridated communities.

IQ scores were collected in two areas of intelligence:

  • Verbal IQ includes verbal reasoning and comprehension.
  • Performance IQ represents nonverbal reasoning, spatial processing, and visual motor skills.

The American Fluoridation Society (AFS) welcomes robust research on fluoride and fluoridation. However, we are concerned that the JAMA Pediatrics study may produce headlines that do not accurately reflect the study's data and methodology.

Recent research

Before taking a closer look at this study, it's essential to consider the context. In recent years, multiple studies have found no link between fluoride exposure and intelligence/cognitive skills.

Johnny Johnson Jr., DMD, president of the American Fluoridation Society.Johnny Johnson Jr., DMD, president of the American Fluoridation Society.

A 2018 animal study from the National Toxicology Program reported that no fluoride exposure-related differences in motor, sensory, or learning and memory performance were seen (Neurotoxicity Research, February 5, 2018).

The American Journal of Public Health (January 2015, Vol. 105:1, pp. 72-76) published a study from New Zealand that tested subjects' IQs over 30 years. This study found no link between IQ scores and whether someone grew up living in a fluoridated community.

Like the U.S., New Zealand is a nation where fluoridation programs are common.

Swedish health economists examined the long-term effects of fluoride exposure on people's outcomes in the labor market in an unpublished 2016 study. Although Sweden doesn't have local fluoridation programs, the economists compared labor market outcomes with varying concentrations of fluoride in tap water across the country. The study authors concluded that there was no effect on cognitive ability, noncognitive ability, or education.

When the JAMA Pediatrics study was released, the American Academy of Pediatrics reaffirmed its support for community water fluoridation.

"There are thousands of articles pointing to the safety of community water fluoridation, and we need to continue to look at the impacts, but this study doesn't change the benefits of optimally fluoridated water and exposure to fluoride," stated Patricia Braun, MD, MPH, professor of pediatrics at the University of Colorado and and chair of the academy's Section on Oral Health Executive Committee.

Caution required

Let's consider some of the reasons why leading health officials are viewing this study with appropriate caution:

1. Data

Grainne McAlonan, PhD, a professor of translational neuroscience at the Sackler Institute for Translational Neurodevelopment at King's College in London, reviewed the study and told the Science Media Centre that caution was needed when looking at the data.

"If you look at average IQ in the children from fluoridated and nonfluoridated groups, these are virtually the same: 108.07 vs. 108.21, respectively. I was, therefore, surprised that the study went on to look for a relationship between fluoridation and IQ, given these figures."

2. Reliable exposures

“The American Fluoridation Society welcomes robust research on fluoride and fluoridation.”

The fluoride exposures which the JAMA Pediatrics study relied on are not very reliable. It was based on "spot urine samples" instead of 24-hour samples, which most scientists consider the most reliable type of urine sample.

Alastair Hay, PhD, an emeritus professor of environmental toxicology at the University of Leeds, told the Science Media Centre that the use of spot samples was a "crucial failure" of the study.

"For a substance with a short half-life, such as fluoride, urine concentrations vary hugely and are really only representative of the last drink," Hay added. "Validation of intake is something you must do before looking at associations."

3. Gender

The gender differences have no clear explanation. Higher fluoride exposure among Canadian boys was associated with lower IQ scores, but higher exposure for girls was linked to slightly higher IQ scores.

The study authors were unable to explain why such a gender difference would exist. With a neurotoxicant, the expectation is that both sexes would be affected, Hay stated.

"I find these sex differences difficult to explain," he told Science Media Centre.

4. Additional factors

Other factors could have skewed the study's results. When designing and conducting an IQ study, it is crucial to consider all the other factors (confounders) that could have affected the results. This is particularly challenging for the topic of human intelligence because a wide range of factors can shape a child's IQ.

Other potential confounders include lead, the mother's educational achievement, and socioeconomic status.

Tooth decay is the most common chronic disease for children and teens, according to the U.S. Centers for Disease Control and Prevention. Additionally, tooth decay is a lifelong disease that affects adults and our aging population. Fluoride in drinking water, toothpaste, and other modes helps to prevent tooth decay and reduces the severity of it. People and communities should not be scared into making a decision that will harm their oral health and overall health.

Johnny Johnson Jr., DMD, is the president of the American Fluoridation Society.

The comments and observations expressed herein do not necessarily reflect the opinions of, nor should they be construed as an endorsement or admonishment of any particular idea, vendor, or organization.

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