In a large, national cohort study, investigators found no evidence that community water fluoridation is associated with adverse birth outcomes, including birth weight, offering reassurance about the safety of this long-standing public health intervention during pregnancy.
The investigators analyzed nearly 11.5 million singleton births across 677 US counties between 1968 and 1988, a period marked by the staggered adoption of community water fluoridation nationwide. Using detailed birth certificate data from the National Vital Statistics System's Natality Detail Files and fluoridation records from the Centers for Disease Control and Prevention Fluoridation Census data, they examined whether prenatal exposure to fluoridated drinking water was associated with changes in infant birth weight or related outcomes.
Change in mean birth weight was the primary outcome, given its role as a widely accepted indicator of infant health as well as its association with long-term health and socioeconomic outcomes. Secondary outcomes included the incidence of low birth weight, gestational length, and incidence of prematurity.
The investigators used an event-study difference-in-differences design to compare changes in birth outcomes within the same counties prior to and following the rollout of community water fluoridation while using counties that never fluoridated or had not yet fluoridated as controls. By focusing on within-county changes over time, this study design reduced the risk that the results were driven by confounding factors or broader secular trends.
Across all analyses, the introduction of community water fluoridation wasn't associated with statistically significant changes in birth weight. The main difference-in-differences estimate showed a change of –0.53 g, a difference that was neither statistically nor clinically meaningful. Event-study analyses similarly found no evidence of changes prior to fluoridation was introduced and no detectable effects afterward, with estimates remaining small across all time periods examined.
The findings extended to secondary outcomes. The investigators noted that community water fluoridation wasn't associated with rates of low birth weight, gestational length, or prematurity. The results were consistent across multiple sensitivity analyses, including models accounting for state-specific time trends and analyses restricted to counties with high fluoridation coverage to reduce potential exposure misclassification.
Concerns about fluoride exposure during pregnancy have increased in recent years, particularly following observational studies suggesting possible links between fluoride and neurodevelopmental outcomes. Some prior studies also reported associations between maternal fluoride exposure and lower birth weight. However, many of those studies relied on cross-sectional designs that were more vulnerable to confounding.
The investigators emphasized that their quasi-experimental approach leveraged the natural variation in fluoridation adoption over time and found no evidence of harm. Even the largest negative estimates observed were less than 1% of the average birth weight, well below thresholds considered clinically relevant.
“This cohort study found that [community water fluoridation] is not associated with infant health as measured by birth weight, contributing to ongoing evaluations of the safety of [the practice], particularly with regard to potential adverse effects during pregnancy,” stated lead study author Benjamin Krebs, PhD, of the Faculty of Business and Economics at the University of Basel in Switzerland. “Our findings contribute to the broader discussion of potential adverse effects of fluoride exposure and highlight the importance of using more rigorous empirical strategies when evaluating population-level interventions,” they concluded.
Co–study author Lisa Simon, MD, DMD, of the Department of Medicine at Brigham and Women’s Hospital, received grants from the National Institute of Dental and Craniofacial Research and CareQuest Foundation as well as personal fees from the California Dental Association, Santa Fe Group, American Dental Association, and Society of Teachers of Family Medicine. The study authors reported no other disclosures.
Source: JAMA Network Open
