A new study in JAMA Network Open (Malin, et al.) claims to have found an association between mothers’ prenatal fluoride levels and later deficiencies in children’s executive function. This study used “spot samples” of maternal urinary fluoride (MUF) to measure a pregnant woman’s overall exposure to fluoride.
Why Spot Samples Are Not Valid for this Study
Experts in assessing exposure to fluoride have determined that MUF can be a valid way to understand exposure on a community level, but not for an individual. Why aren’t spot samples a valid measure of an individual’s fluoride exposure? Fluoride levels vary throughout the day — and from day to day, too. If fluoride concentration in urine is measured at only one point in the day, it is just that – a measure of fluoride at that moment in the day.
By definition, the information from a spot sample is incomplete. Say the urine was collected soon after someone consumed foods that are naturally high in fluoride. It would likely be high when, at a different time, it would be low. And vice versa. The same would be true in reverse.
Convenience Samples
Urine samples are routinely collected during pregnancy. For research purposes, this is known as a “convenience sample”. They are a common source of data for studies like the one from which Malin et al. drew. It may seem intuitive that MUF is both a convenient and sound way to measure a mother’s exposure to fluoride. It is not. To associate an outcome in children with an exposure during pregnancy, the total exposure and other factors must be measured properly. The scientific community is clear on this. Moreover, a convenience sample cannot be used to infer statistical significance that applies to the general population, which would be needed before suggesting any change in medical practice or policy.
Strong Evidence of No Association
In 2023, a study of children in Australia (Do, et al.) also explored the question of whether fluoride and children’s executive function were linked. It found no such association. The Australian study measured fluoride exposure using the status of water fluoridation rather than spot samples. The authors also analyzed a much larger data set, one that included 2,682 children. They studied > 90% more children than Malin et al, who relied on a sample of only 229 children. Those 229 children were from one ethnic group and came from a single city. They were not, therefore, representative of the general population of children. That means that the study’s results describe only a single and small demographic. The findings of the Australian study are more generalizable to a large and diverse population like the U.S. This is important. When public policy recommendations result from research, the data must describe the public.
What comes next? More research, properly designed, is needed on this important question in order to develop a robust body of evidence. Together with evidence on the efficacy and safety of community water fluoridation, only then can clinical recommendations and public policy be evidence-based, consistent and sound. As always, we welcome new research to broaden our understanding on the safety of fluoride when the data are valid, sufficient and purposefully derived.
