Key Takeaways
There was no connection between water fluoridation and birth weight in a large cohort study that analyzed outcomes before and after the element was added to the water supply.
Analyzing more than 11 million singleton births over a 21-year period, there was no association with birth weight after fluoridation was implemented (difference-in-differences estimate ?0.53, 95% CI ?4.75 to 3.70, P=0.81), Matthew Neidell, PhD, of the Columbia University in New York, and colleagues reported in JAMA Network Open.
Changes in birth weight following community water fluoridation were small in magnitude, ranging from ?8.44 g to 7.20 g, they reported.
“What we found was there was no relationship between water fluoridation and birth outcomes — that when an area fluoridates, we don’t see any changes in birth outcomes, either measured by birth weight or gestational length,” Neidell told MedPage Today.
Nikki Zite, MD, MPH, a professor of obstetrics and gynecology at the University of Tennessee Graduate School of Medicine in Knoxville, who was not involved in the study, said it “does provide reassurance that the effective public health measure of community fluoridated drinking water does not cause poor birth outcomes.”
While the benefits of water fluoridation — particularly against dental caries — have been well documented, some studies have raised concerns about potential adverse effects, especially from prenatal and early-life exposure. Much of the research has focused on cognitive outcomes, such as IQ, but those studies have been limited in their ability to address confounding, the researchers noted.
For their study, they focused on birth weight as an alternative outcome, as it’s a widely accepted measure of infant health and has been associated with health later in life, they wrote. Neidell also noted that the in-utero period offers a unique window to “cleanly measure someone’s exposure to water fluoridation,” since fluoride crosses the placenta.
They used an event-study difference-in-differences design that analyzed the staggered rollout of community water fluoridation across the U.S. over several decades, from January 1968 to December 1988, using the CDC’s 1992 Water Fluoridation Census. Counties that didn’t fluoridate were used as controls. Birth outcomes were obtained from the National Vital Statistics System’s Natality Detail Files.
Of the 677 counties analyzed, 60.3% had community water fluoridation while 39.7% were never treated across the 21-year period. Mean gestational age was 39.5 weeks and mean birth weight was 3,337.4 g. Most mothers were between 20 and 29, and 84% were white.
In sensitivity analyses, there was no association between fluoridation and the proportion of low birth weight, gestational length, or risk of prematurity, they reported. “Consistent with the birth weight results, we found no evidence of a pretrend or any other association between [community water fluoridation] and these outcomes,” they wrote.
The study was limited because it measured fluoride exposure at the community level, rather than the individual, which carries the possibility of exposure misclassification. They also noted that other trends could have occurred simultaneous to fluoridation, such as incorporating other additives and treatment strategies.
Still, they concluded that the 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.”
Zite added that in her practice, she sees significant dental disease in populations that rely on well water.
“There are significant negative consequences to poor dental hygiene in pregnancy, so I had always been confused by the negativity around safe levels of fluoride being added to drinking water,” Zite said. “This study should be helpful to dispel the myths or fears about safe levels of fluoride being added to water.”
Original article online at: https://www.medpagetoday.com/obgyn/pregnancy/119495