A large study released Tuesday found no connection between fluoridation in the United States and lower birth weight or premature births, important measures of infant health.
Public health authorities have long recommended adding fluoride to the nation’s water to strengthen teeth and prevent cavities. The Centers for Disease Control and Prevention listed fluoridation as one of the 10 great public health wins of the 20th century.
But Health Secretary Robert F. Kennedy Jr. has called fluoride “neurotoxic and carcinogenic,” tying the mineral to I.Q. loss and neurodevelopmental problems, and urged states to ban its use in drinking water. Last year, Utah and Florida each passed a ban, and at least 19 other states considered similar measures. In October, the Food and Drug Administration issued new recommendations against prescribing fluoride supplements to some children.
The new analysis did not examine if fluoride affected I.Q. scores. “That’s the question everyone is freaking out about,” said Dr. F. Perry Wilson, the director of the Yale Clinical and Translational Research Accelerator.
But it did provide the most robust research around birth weight, a predictor of long-term health and educational attainment, among other things, said Dr. Scott Tomar, a public health dentist and oral epidemiologist at the University of Illinois Chicago, who was not involved with the study. “It’s hard to imagine a larger, more comprehensive look at the association between fluoride exposure and birth weight,” he said.
The study, published in JAMA Network Open, analyzed birth records for more than 11 million infants born in the United States from 1968 to 1988. The researchers compared the birth weights of babies born in counties before and after any water fluoridation began, and found no difference. To account for broader changes over time, like improvements to maternal and newborn care, the researchers also compared birth weights in counties that began fluoridating drinking water with birth weights in those that didn’t.
No matter how the data was sliced, there was no change in birth weight after water fluoridation began, said Matthew Neidell, an economist at Columbia University Mailman School of Public Health and the senior author of the new study.
Previous studies found that fluoride was tied to lower birth weight. But they were smaller than the new study, and did not follow communities over time.
Last year, a large analysis tied high fluoride levels to lower I.Q., but it did not include any research conducted in the United States, where fluoride levels are generally very low. The researchers also didn’t find any definitive association between low amounts of fluoride and I.Q. Many of the studies didn’t account for other important factors that shape a child’s development either, like parental income and home environment.
I.Q. scores are also a complicated endpoint since not every child is tested and results can swing from one test to the next, particularly in young children.
Birth weight is a more standardized measure, and because it is almost always measured immediately after birth, Dr. Neidell and his team could focus on only the window of pregnancy, not years of environmental influences on children.
Some scientists have proposed that fluoride might affect a child’s I.Q. through a mother’s thyroid function. But that mechanism is hard to square with the new results, Dr. Tomar said, because thyroid problems in pregnancy also tend to influence birth weight.
“In general, birth weight and brain weight are aligned,” said Dr. Patricia Braun, a pediatrician at Denver Health.
The new research doesn’t prove causation and didn’t settle every question. For example, it didn’t assess if water boards made other upgrades when starting fluoridation, like changing disinfectant procedures or adding anti-corrosive agents during treatment, Dr. Wilson said. If those changes affected birth weight, they could have masked any potential harm or benefit from fluoride itself, he added.
And counties don’t always fluoridate all their water at once, so not every pregnant woman would immediately have access to treated water, Dr. Braun said. The researchers tried to address this by also comparing counties with nearly universal fluoridation — at least 90 percent coverage — with counties that had no fluoridated drinking water.
Still, they found no difference in birth weights.
Even if the results can’t rule out health risks from water fluoridation, Dr. Wilson said, the unproven harms need to be weighed against the well-documented benefits, especially for children who do not have regular dental care.
“I’m never going to come out and be like, ‘There’s absolutely no risk of fluoride,’” Dr. Wilson said. “But I am quite confident that the risk is very small, if it exists at all.”
Simar Bajaj covers health and wellness for The Times.
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