Fluoride in Drinking Water Linked to Type 2 Diabetes

Fluoride in the drinking water – put there to protect from dental cavities – has been linked to type 2 diabetes (T2D), according to research recently published in the Journal of Water and Health.

The paper, authored by Kyle Fluegge, PhD, when he was a post-doctoral fellow in the Department of Epidemiology and Biostatistics at Case Western Reserve University School of Medicine, points out that fluoridation with sodium fluoride could be a contributing factor to skyrocketing diabetes rates in the U.S., since the chemical is a known preservative of blood glucose. For this study, Fluegge uses mathematical models to analyze publicly available data on fluoride water levels and diabetes incidence and prevalence rates across 22 states. He adjusts for obesity and physical inactivity collected from national telephone surveys to help rule out confounding factors. Two sets of regression analyses suggested that supplemental water fluoridation was significantly associated with increases in diabetes between 2005 and 2010.

“The models indicate that natural environmental fluoride has a protective effect from diabetes. Unfortunately, natural fluoride is not universally present in the water supply.”

“The models look at the outcomes of [diabetes] incidence and prevalence being predicted by both natural and added fluoride,” says Fluegge.

Fluegge reports that a one milligram increase in average county fluoride levels predicted a 0.17% increase in age-adjusted diabetes prevalence. Digging deeper revealed 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. The positive association between fluoridation and diabetes was discovered when Fluegge 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,” says Fluegge. “Only using the concentration [of added fluoride] does not produce a similarly robust, consistent association.” For this reason, Fluegge adjusted his calculations to incorporate tap water consumption, instead of sticking to calculations that rely on “parts per million” measurements of fluoride in the water.

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

Fluegge used several estimations in his study, including calculations of county-level water fluoride levels; per capita county tap water consumption; and county measures of poverty, obesity, and physical inactivity. Although he doesn’t suggest the study should trigger policy changes, he does indicate it should serve as a call for additional research on the important association between fluoridation and diabetes. “This is an ecological study. This means it is not appropriate to apply these findings directly to individuals,” says Fluegge. “These are population-level associations being made in the context of an exploratory inquiry. And water is not the only direct source of fluoride; there are many other food sources produced with fluoridated water.”

In addition to being found in food like processed beverages or produce exposed to specific pesticides, fluoride is found naturally in water in the form of calcium fluoride. Supplemental fluoride was first added to community water supplies in the 1940s. “The models indicate that natural environmental fluoride has a protective effect from diabetes,” Fluegge says. “Unfortunately, natural fluoride is not universally present in the water supply.”

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