Sodium Fluoride Disrupts Brain Chemistry and Behavior in Rats

Fluoride has long been celebrated as one of public health’s most effective tools against tooth decay, added to drinking water supplies and dental products across much of the world. But a growing body of research is raising uncomfortable questions about what happens when exposure exceeds recommended levels, particularly for the brain. A new study published in Discover Toxicology has now provided some of the most detailed evidence to date that prolonged sodium fluoride exposure can rewire brain chemistry, damage myelin, and alter behavior in adult animals. The work, led by Ademola Adetokunbo Oyagbemi of the University of Ibadan in Nigeria alongside a large international team, tracked Wistar rats exposed to graded doses of sodium fluoride for 30 and 60 days and found a cascade of neurological damage spanning behavior, biochemistry, and brain structure.

The experimental design was deliberately comprehensive. Eighty-four adult male Wistar rats, each weighing between 100 and 120 grams, were randomly assigned to six groups. One group served as a control and received only deionized water, while the remaining five groups received sodium fluoride dissolved in deionized water at concentrations of 25, 50, 100, 150, and 300 parts per million, equivalent to 25 to 300 milligrams per liter. These doses deliberately exceed the World Health Organization guideline value of 1.5 milligrams per liter for fluoride in drinking water, but they fall within or above concentrations actually reported in groundwater from regions where fluorosis is endemic, making the findings directly relevant to millions of people worldwide who rely on fluoride-contaminated water sources. Seven rats from each group were evaluated at the 30-day mark and seven at 60 days, allowing the researchers to distinguish short-term from longer-term effects.

Behavioral testing using the open field assay revealed striking disturbances in both locomotion and anxiety-like behavior. In the 30-day exposure groups, rats receiving 25 milligrams per liter traveled significantly shorter distances and moved more slowly than controls, while animals at 50, 150, and 300 milligrams per liter showed significant reductions in maximum speed. Perhaps most tellingly, the treated rats exhibited disrupted movement patterns: increased angular velocity and meandering, reduced ability to maintain a straight path, and elevated anticlockwise rotation. Rats at the highest dose of 300 milligrams per liter showed markedly reduced freezing latency, suggesting an anxiety profile fundamentally different from controls. At 60 days, the pattern shifted, with some doses increasing distance traveled while others decreased mobility time, altered freezing behavior, and disrupted path efficiency, indicating that the behavioral consequences of fluoride exposure evolve over time rather than simply worsening in a linear fashion.

Beneath these behavioral changes, the biochemical assays painted a picture of severe oxidative stress in two critical brain regions, the hippocampus and the striatum. Malondialdehyde, a marker of lipid peroxidation and cellular membrane damage, rose in a dose-dependent fashion after 30 days of exposure. Hydrogen peroxide levels climbed while the brain’s antioxidant arsenal collapsed: reduced glutathione, superoxide dismutase, and glutathione peroxidase all declined significantly across treated groups. The brain is especially vulnerable to this kind of oxidative assault because it consumes enormous quantities of oxygen and is packed with polyunsaturated fatty acids that are prime targets for free radical attack. The researchers note that fluoride appears to suppress antioxidant defenses both directly, through competitive inhibition of protective enzymes, and indirectly, by generating a flood of reactive oxygen species that overwhelms them.

One of the most consistent findings across every dose and every time point was a significant reduction in acetylcholinesterase activity in both the hippocampus and the striatum. Acetylcholinesterase is the enzyme responsible for breaking down acetylcholine, a neurotransmitter central to learning, memory, attention, and motor control. Its inhibition means acetylcholine lingers longer at synapses, disrupting normal cholinergic transmission. This mechanism is pharmacologically significant because acetylcholinesterase inhibition is also the mode of action of certain nerve agents and pesticides, and reduced cholinergic transmission is implicated in cognitive decline. The authors suggest that the disrupted motor function and altered emotional states observed in the open field tests may be directly linked to this cholinergic impairment, providing a mechanistic bridge between molecular chemistry and observable behavior.

The immunohistochemical analysis added structural evidence to the biochemical story. In the striatum, the researchers documented elevated immunoreactivity for glial fibrillary acidic protein, or GFAP, a hallmark marker of astrocyte activation. Astrocytes normally support neurons by secreting neurotrophic factors, but when they proliferate excessively in response to injury, a process called astrogliosis, they can obstruct neurite outgrowth and impede tissue regeneration. After 60 days of exposure, the increase in astrocyte population was particularly pronounced. Gliosis is the brain’s intrinsic response to damage, and its presence here confirms that sodium fluoride exposure registers in the brain as genuine injury rather than a transient, reversible perturbation.

Equally concerning was the fate of the myelin sheath, the fatty insulation that wraps nerve fibers and enables rapid, efficient signal transmission. Rats exposed to sodium fluoride for both 30 and 60 days showed significantly reduced immunoreactivity for myelin basic protein in the corpus callosum, the massive fiber bundle connecting the brain’s two hemispheres. Demyelination is a serious form of neurological damage, characteristic of diseases such as multiple sclerosis, and its occurrence following chemical toxicity is well documented. The loss of myelin basic protein indicates breakdown of the intact myelin sheath, which would slow or scramble communication between brain regions and could plausibly underlie the motor coordination deficits and abnormal movement patterns recorded in the behavioral tests. Previous research has shown that fluoride can induce degenerative changes across the brain and spinal cord, including axonal degradation, mitochondrial impairment, and synaptic ultrastructural changes, and this study adds region-specific myelin loss to that inventory of harm.

Integrating these findings, the authors propose a coherent mechanistic chain: sodium fluoride exposure generates reactive oxygen species, depletes antioxidant defenses, and drives lipid peroxidation; this oxidative environment damages cholinergic neurons and triggers astrocytic proliferation; the resulting neuroinflammation and myelin degradation cumulatively degrade motor function, coordination, and anxiety regulation. The study’s strength lies in this multi-level convergence, linking behavioral observation with biochemical assay and structural histology in the same animals, something many earlier single-endpoint studies could not do. The connection to human health is not lost on the researchers, who note that epidemiological studies in regions with fluoride levels far exceeding WHO standards have reported significantly lower IQ scores in children, and that both juvenile and adult subjects exposed to elevated fluoride show diminished learning capacity and memory deficits.

The authors are careful to acknowledge the limitations of their work. All experiments were conducted in male rats, and since sex-specific differences in toxin susceptibility are widely reported, the findings may not fully generalize to females. Future studies incorporating female animals will be needed to determine whether these effects are sex dependent. The doses used, while environmentally relevant to fluorosis-endemic regions, sit well above typical fluoridated municipal water levels, so the results should not be read as an indictment of water fluoridation at recommended concentrations. Nevertheless, for the substantial populations in countries including Nigeria, India, Kenya, and China who drink groundwater with fluoride concentrations matching or exceeding those tested here, the implications are sobering. The study demonstrates that fluoride at these levels compromises brain health through oxidative stress, astrocytosis, and disrupted myelination, ultimately producing measurable neurobehavioral impairment, and it provides a detailed mechanistic framework that future protective interventions, whether antioxidant, cholinergic, or anti-inflammatory, can now be tested against.

Subject of Research: Neurotoxic effects of 30- and 60-day sodium fluoride exposure on behavior, brain chemistry, and myelin integrity in adult Wistar rats

Article Title: 30- and 60-days exposure of sodium fluoride induces neurobehavioral deficits and alters neurochemical parameters in adult Wistar rats

Article References: 30- and 60-days exposure of sodium fluoride induces neurobehavioral deficits and alters neurochemical parameters in adult Wistar rats. (n.d.). https://doi.org/10.1007/s44339-026-00051-3

Image Credits: AI Generated

DOI: 10.1007/s44339-026-00051-3

Keywords: sodium fluoride, neurotoxicity, oxidative stress, Wistar rats, acetylcholinesterase, myelin basic protein, GFAP, hippocampus, striatum, corpus callosum, neurobehavioral deficits, fluoridation