Fluoride has long been an effective tool in fighting tooth decay. But research from Case Western Reserve University (CWRU) investigated whether it has added to the growing rates of diabetes in the United States since it is a known preservative of blood glucose.

Kyle Fluegge, PhD, used mathematical models to analyze publicly available data on fluoride water levels and diabetes incidence and prevalence rates in 22 states. He also included adjustments for obesity and physical inactivity collected from national telephone surveys to rule out confounding factors.

“The models look at the outcomes of [diabetes] incidence and prevalence being predicted by both natural and added fluoride,” said Fluegge, who performed his research as a post-doctoral fellow at the CWRU School of Medicine.

Now, Fluegge is a health economist with the Division of Disease Control for the New York City Department of Health and Mental Hygiene and co-director of the Institute of Health and Environmental Research in Cleveland, Ohio.

Two sets of regression analyses suggested that supplemental water fluoridation was significantly associated with increases in diabetes between 2005 and 2010. A 1.0 mg increase in average county fluoride levels predicted a 0.17% increase in age-adjusted diabetes prevalence.

Also, Fluegge found differences between the types of fluoride additives used by each region. The additives linked to diabetes in the analyses included sodium fluoride and sodium fluorosilicate. Fluorosilicic acid seemed to have an opposing effect and was associated with decreases in diabetes incidence and prevalence.

Counties that relied on naturally occurring fluoride in their water and did not supplement with fluoride additives also had lower diabetes rates. Fluegge found the positive association between fluoridation and diabetes when he adjusted fluoride exposure levels to account for estimated per capita tap water consumption.

“The models present an interesting conclusion that the association of water fluoridation to diabetes outcomes depends on the adjusted per capita consumption of tap water,” said Fluegge. “Only using the concentration [of added fluoride] does not produce a similarly robust, consistent association.”

As a result, Fluegge adjusted his calculations to incorporate tap water consumption instead of sticking to parts-per-million measurements of fluoride in the water. He also used several estimations, including calculations of county-level water fluoride levels, per capita county tap water consumption, and county measures of poverty, obesity, and physical activity.

Fluegge doesn’t suggest that his work should trigger policy changes. However, he does indicate that it should serve as a call for additional research on the association between fluoridation and diabetes.

“This is an ecological study. This means it is not appropriate to apply these findings directly to individuals,” said Fluegge. “These are population-level associations being made in the context of an exploratory study. And water is not the only direct source of fluoride. There are many other food sources produced with fluoridated water.”

Furthermore, Fluegge noted, his models indicate that natural environmental fluoride has a protective effect from diabetes, though it is not universally present in water supplies.

The study, “Community Water Fluoridation Predicts Increase in Age-Adjusted Incidence and Prevalence of Diabetes in 22 States from 2005 and 2010,” in the Journal of Water and Health.

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