Reexamining An Unquestioned Staple: Fluoride

In 1901, the research of fluoride began: college graduate Frederick McKay arrived in Colorado Springs, Colorado, to open his own dental practice. However, he found something unexpected: the Colorado natives had grotesque brown stains on their teeth; some teeth were even entirely the color of chocolate candy. This phenomenon came to be known as Colorado Brown Stain, but, as McKay soon learned, there was no mention of the brown-stained teeth condition in any literature. Residents blamed it on arbitrary factors, such as eating too much meat, consuming inferior milk, etc. But McKay was skeptical. After a few experiments, McKay and local practitioners found that the brown teeth were resistant to decay. The mystery gained traction in 1923 when McKay met with a couple whose children's teeth were stained. They explained that the stains began appearing shortly after the town had started construction of a communal water pipeline. McKay analyzed the water from the pipeline but found nothing alarming in it; just to be safe, though, he advised town leaders to abandon the pipeline altogether. And within a few years, the children of the town were sprouting healthy secondary teeth without any stains. And after 30 years of research, he had finally found the answer: high levels of fluoride in drinking water had caused the discoloration of tooth enamel (“The Story of Fluoridation”). McKay’s research started a frenzy for scientists around the nation, who eventually came to the conclusion that only the small amounts of fluoride in water could protect teeth from decay. Because of this groundbreaking discovery, by the early 1950s, long before the early trials to test the effects had been completed, most dentists, doctors, and biochemists agreed that water fluoridation would save children’s teeth without harming anyone else (Carstairs). 

Looking back, some scientists note that the evidence used to show that community water fluoridation (CWF) protects against tooth decay was conducted before the use of fluoridated toothpaste and was largely based on observational or “association” studies; smoking, air pollution, and asbestos were also all observational studies early on (“Controversy: The Evolving Science of Fluoride: When New Evidence Doesn’t Conform With Existing Beliefs”). In fact, none of the studies found ever tested the effects of ingested fluoridated water on gut health before water was artificially fluoridated in the U.S. (Moran et al.). Not only that, but the studies at that time likely included bias and uncontrollable variables (Iheozor-Ejiofor et al.). Therefore, the research that deemed it “safe” to put in public water was not legitimately substantial enough for scientists to distribute it on a national scale. The lack of studies even today, 80 years after water was first fluoridated, shows that the scientific community needs to rethink its values. Even with new evidence uncovering the potentially detrimental effects on the human microbiome, scientists refused to adapt their current beliefs, as evidenced by article titles like “Fluoride won’t make you dumber, but the ‘debate’ about its safety might” (Moran et al.). The evidence that scientists use to support their beliefs is based on loose observational studies only examining a small part of the human body. New discoveries are made every day in the science field, and theories change constantly; scientists attempting to hang on to a 100-year-old theory are hurting children around the globe. For what? So don't they have to admit they made a mistake by adding fluoride to water without doing proper research? For marketing it as perfectly safe and adding it to every American's daily life? The purpose of this paper is to change one mind at a time. To spread the word and, hopefully, in the future, make a change. 

Nevertheless, despite the questionable research practices, fluoride is still in drinking water in many countries like the U.S., Brazil, Canada, Chile, China, and more to prevent tooth decay (Moran et al.). According to the CDC’s 2022 Water Fluoridation Statistics, 63% of people in the U.S. receive fluoridated water (“2022 Water Fluoridation Statistics”). Many of the studies used in this paper are from China, India, etc., to show the toxic effects of fluoride at high levels; most of these waters are naturally fluoridated or polluted, with little to no government regulation. The sources of fluoride in daily life all over the world include water, food (milk and salt are all commonly fluoridated (CHE)), dental products, and air sources that come from coal burning, oil refining, steel production, brick-making industries, phosphatic fertilizer plants, pesticides, and sewage (AD HOC SUBCOMMITTEE ON FLUORIDE). The fluoride put into tap water in the U.S. is usually a byproduct of phosphate fertilizer factories (Jha et al.). It's worth noting that the FDA regulates fluoride amounts in dental aspects such as toothpaste, composite fillings, and dental cements; as well as in bottled water; water used in food processing, infant formula, dietary supplements, and more. However, the FDA does not regulate fluoride in drinking water (AD HOC SUBCOMMITTEE ON FLUORIDE). The U.S. Environmental Protection Agency (EPA), the U.S. Public Health Service (PHS), and the Centers for Disease Control and Prevention (CDC) all play a part in the regulation of fluoride in tap water. For context, in the late 1960s, fluorine pollution was damaging crops, killing fish, and causing harmful skeletal fluorosis in cattle. This was caused by factories dumping concentrated chemicals like fluoride into Tampa Bay’s waterways. The EPA became concerned and started to enforce regulations on these toxic facilities (Fluoride and the Phosphate Connection). At the time this took place, the full effects of fluoride were widely unknown, and it was assumed that these harms to the environment were due to all the chemicals combined. However, skeletal fluorosis is just one example of an effect of fluoride, not all of the pollutants combined—just one. A toxic one.

 The positive effects of fluoride are well known, even in spite of using fluoride toothpaste, and this study in particular highlights the effect quite well (Brito Marques et al.). In April 2025, 2,649 second-graders, around seven years after fluoridation ended in their town, were surveyed in Canada; they have never been exposed to fluoridated water before. Of those children, 65% had tooth decay. Meanwhile, in a different town that had continued fluoridating their water, only 55% of surveyed children had experienced tooth decay (Viveros). This study focuses on the positive effect on teeth, a common support to current scientists’ theories. In a study investigating the harmful fluoride levels on teeth, scientists discovered that levels of up to 1 mg/L of fluoride in water did not cause dental fluorosis in most people (Strunecka and Strunecky).

An evaluation by the National Research Council (NRC) in 2006 found an “association between consumption of high levels of naturally occurring fluoride in drinking water and adverse neurological effects in humans and recommended further investigation” (National Toxicology Program). Estimates in 1990 provided by the CDC showed that approximately 132 million people in the U.S. received drinking water with fluoride levels higher than 0.7 mg/L (the CDC recommendation to prevent cavities) (AD HOC SUBCOMMITTEE ON FLUORIDE). This means that even studies that advocate that fluoride is safe under .5mg/L, are not relevant to the 132 million Americans drinking over 0.7mg/L. Toothpaste can account for up to 25% of the total systemic dose for children aged between 2 and 6 years, depending on the amount of toothpaste swallowed during brushing (Guth et al.). Between 1994 and 2011, accidents where young children swallowed fluoride happened seven times more often. Younger children generally ingest a higher proportion of toothpaste than older children, ingesting over half of the toothpaste per brushing, which results in the child having 5.56 times more of a chance at developing fluorosis (more on this later) (Nakamoto and Rawls). In 2018-2020, 1700 drinking water samples were taken in 29 cities of Fars Province. The results showed that the concentration of fluoride in the water was in the range of 0.086 to 2.61 mg/L (the WHO’s maximum fluoridation level is 1.5 mg/L). In 48.27% of the cities, fluoride was below international standards; 34.48% of the cities were in the permissible range of 0.5 to 1.5 mg/L, and 17.24% of the areas had fluoride contents above the safe range. Hazard quotient index determined that 27.58% of children, 17.24% of teenagers, and 10.34% of adults had the risk of diseases from excessive fluoride intake (Ghanbarian et al.). 

In 2016, the National Toxicology Program published a review of the results from experimental testing on animals on the effects of fluoride. A low to moderate amount of the evidence showed that deficits in learning and memory were caused by the effects of fluoride, and around 70 studies have been performed assessing the relationship between fluoride exposure and children’s IQ (National Toxicology Program). More memory effects research arose, assessing around 30 studies and finding an average IQ decrease of around seven points in children exposed to raised fluoride concentrations (Choi et al.). So far, over 63 studies have found an association between elevated fluoride exposure and reduced IQ in over 23,872 children (Strunecka and Strunecky). In addition to IQ deficits, animal studies have shown impairment of concentration, new learning ability, and short-term memory (EFFECTS OF HIGH FLUORIDE AND ARSENIC ON BRAIN  BIOCHEMICAL INDEXES AND LEARNING-MEMORY IN RATS). Fluoride is commonly used as a pesticide, as it kills insects and plants; it’s no surprise that toxic results were found when properly examined. Almost all studies examining the effects of fluoride were performed in poor, rural communities in China, Iran, Mongolia, etc., where the drinking water contains higher levels of fluoride than the control populations, who often had access to water that was fluoridated at the recommended level (Guth et al.). This discrepancy in the studies may have led to false reports and skewed effects since the control group isn’t without fluoride. The guidelines of these studies also prevent the results of accurate research on the effects of fluoride at the recommended levels in contrast with absolutely no fluoride intake. Even though these studies do not provide enough backing to declare fluoride toxic at levels deemed by the WHO as “safe,” these studies still prove that fluoride is toxic at high levels. 

Infants are the most at risk, as they may intake even a grown adult's recommended level set by the government. Infants obtain fluoride through the mother’s breast milk and/or infant formula with boiling water, which increases the concentration of fluoride as the water evaporates (AD HOC SUBCOMMITTEE ON FLUORIDE). Fluoride intake among infants younger than six months may exceed the tolerable upper limits if they are fed exclusively with formula reconstituted with fluoridated tap water. Researchers in China found that the fetal brain is highly susceptible to fluoride poisoning since the fetal blood-brain barrier is not fully developed and readily permeable to fluoride. The daily fluoride intake should be no more than 0.05 mg/day for infants. Evidence found of fluoride exposure during infancy predicts delayed brain development and thus diminished non-verbal intelligence in children (Nakamoto and Rawls) (Strunecka and Strunecky). A 1-mg higher daily intake of fluoride among pregnant women was associated with a 3.66 lower IQ score in boys and girls. In the study, maternal exposure to higher levels of fluoride during pregnancy was associated with lower IQ scores in children aged 3 to 4 years (Green et al.). 

Although fluoride has been seen to have some beneficial effects on teeth and bone, higher exposure levels to fluoride can result in structural defects such as dental and skeletal fluorosis (AD HOC SUBCOMMITTEE ON FLUORIDE). Dental fluorosis appears in 43–63% of children in certain areas of China with total fluoride intake ranging from 2.7–19.8 mg/day. And while the U.S.’ water doesn’t reach as high of fluoride levels, fluorosis is an issue in the U.S. The symptoms of fluorosis vary from effects on tooth enamel, migraines, and loss of appetite to severe pathological disturbances. These include dental and skeletal fluorosis; hypothyroidism, which 47% of children living in a New Delhi neighborhood with an average water fluoride level of 4.37 mg/L have; sleep disorders; inflammations; IQ deficits; and possibly autism, which has been associated with oxidative stress (Susheela et al.) (Strunecka and Strunecky). Studies have shown that peak fluoride absorption is achieved within 30-60 minutes after ingestion, and absorption ranges from 90-100%. Approximately half of the fluoride absorbed each day will be deposited in the calcified tissues, which have 99% of the fluoride in the body (AD HOC SUBCOMMITTEE ON FLUORIDE). In muscles, a high concentration of fluoride over a long term causes loss of muscle proteins, leading to atrophy (Nagendra et al.). In bones, fluoride alters osteogenesis by replacing calcium, thus resulting in bone deformities associated with skeletal fluorosis. The effects of severe skeletal fluorosis may include severe stiffness and pain, calcification of the spine, osteosclerosis, bone deformities, and neurological problems due to pressure from bones. Fluoride is able to integrate into the bones' crystalline structure, and while this is currently viewed as a benefit because it strengthens the structure, preventing cavities, it also means that fluoride has access to the structure and can cause problems. Osteosarcoma, a rare malignant bone tumor most commonly occurring in children and young adults, is reported to be associated with higher serum fluoride levels and high fluoride bone content. Fluoride alters dentinogenesis, thereby affecting the tooth enamel formation (Nagendra et al.). Children’s teeth are more hydrated and constantly remodeling and therefore absorb more fluoride than the elderly (AD HOC SUBCOMMITTEE ON FLUORIDE). However, Turner et al. concluded that high-dose fluoride treatment did not improve, but decreased, bone strength in rabbits, even in the absence of impaired mineralization (Turner et al.). The U.S. Environmental Protection Agency has set a maximum contaminant level of 4.0 mg/L for drinking water to protect against skeletal fluorosis. WHO indicates a clear risk of skeletal fluorosis for a total intake of 14 mg of fluoride per day, but even 4-8 mg/L proves to have a risk (Strunecka and Strunecky). Skeletal fluorosis impacts millions of people in regions with high natural levels of fluoride, like India (where 80% of water sources are above the WHO’s recommended limit to protect against skeletal fluorosis), China, Pakistan, Iran, and many more.

In humans, the toxic effect of fluoride is believed to cause ADHD, blood–brain barrier, glucose transporter, reduced glutathione, interleukins, and reactive oxygen species (Żwierełło et al.). It can play a part in organelle damage; oxidative stress on the cellular level, which may cause diabetes, neurological diseases, cancer, and rapid aging; cell cycle disruption; inflammatory cytokine secretion; induction of apoptosis (programmed cell death) even in healthy cells; and disruption of synaptic neurotransmission. Many researchers believe that oxidative stress is the primary role of fluoride toxicity since it decreases the level of GPx (an enzyme that protects cells from oxidative damage). Lie et al. revealed a significant positive relationship between excess fluoride exposure from drinking water and prevalence of carotid artery atherosclerosis—a condition where plaques of fat, cholesterol, calcium, and other substances build up and significantly increase the risk of stroke—in adults living in fluoride-endemic areas (Liu et al.). Fluoride is an endocrine disruptor that can lead to thyroid dysfunction as well as being a growth inhibitor, according to Jianjie et al.’s study on zebrafish (Żwierełło et al.) (Jianjie et al.). Nakamoto and Rawls identified a relationship between fluoride and the thyroid hormone (FT3/FT4) as well as the concentration of TSH among older children. Results showed that for every 1 mg/L increase of fluoride causes a 0.13 µ/mL increase in TSH. Similarly, for every 1 mg/L increase of fluoride in urine, there was a 0.09 µg/dL decrease in T4. Even in concentrations less than half a milligram, fluoride still affects thyroid hormone levels. Hypothyroidism was found almost twice as often in fluoridated areas where the study was conducted in England in comparison to non-fluoridated areas. Another part of the study found that a mother who suffered from hypothyroidism was more likely to have a child with a lowered IQ (Nakamoto and Rawls). More research on fluoride's role in the interaction of thyroid hormones is “desirable for recognizing underlying thyroid derangements and its impact on fluorosis” (Singh et al.).

 Pollution from factories is a major problem, as many chemicals are produced and transferred to the air and water nearby. Fluoride and arsenic together are noteworthy as they’re associated with deregulation of autophagy, the process cells use to break down and recycle used components (Tian et al.). At lower concentrations than the concentrations it takes when it is working alone, fluoride combines with aluminum and acts as a false signal in G protein cascades of hormonal and neuronal regulations, which might contribute to unexpected epidemics in the future, as the G protein helps regulate heart rate, sensory perception, immune responses, and hormone secretion. In fact, workers and people living near an aluminum smelting factory where fluoride and aluminum were both of high concentration in the atmosphere suffered from “psychiatric and neurological disturbances” (Strunecka and Strunecky). Similarly, in animal studies, distinctive alterations in the brain have been observed with the chronic administration of aluminum fluoride (AlF₃). According to Mullenix et al., hyperactivity and cognitive deficits can be correlated with hippocampus damage induced by sodium fluoride (NaF). These findings indicate that the performance of daily physical activity could reduce the negative effects of the chronic ingestion of NaF on glucose homeostasis (Lombarte et al.). Tissue fluoride levels of the hippocampus, neocortex, cerebellum, spinal cord, and sciatic nerve all increased significantly in fluoride-treated rats, indicating rapid absorption through the blood-brain barrier, suggesting that fluoride collects in tissue. Neurodegeneration was clearly evident in the hippocampus, neocortex, cerebellum, spinal cord, and sciatic nerve on fluoride exposure (Kumar et al.). Many people argue that many studies done on the negative effects of fluoride are done at such high levels of fluoride that they are irrelevant however, these effects can still be compared to places like China and India where fluoridation is dangerously high. Even though the effects of fluoride in smaller concentrations aren’t as severe, that doesn’t mean we can ignore them completely as fluoride builds up overtime and is still too high for unborn babies to be ingesting.

Currently about 20% of pharmaceutical drugs contain fluorine, so it is vital to understand what role it plays when interacting with drugs (Strunecka and Strunecky). In Kupnicka et al., it was observed how fluoride ions influenced the phenomenon of morphine dependence in a model expressing withdrawal symptoms. The degenerative changes caused by toxic activity of fluoride ions during the developmental period of the nervous system may impair the functioning of the dopaminergic pathway due to changes in dopamine concentration and in dopamine receptors (Kupnicka et al.). As many opioids like morphine use the dopamine receptor to activate the “feel good” hormone, it could be detrimental if fluoride causes the period dopamine is released to be prolonged, making it even harder to quit drugs, raising suicide rates after quitting, and potentially affecting the dopamine pathway even without the use of drugs. If more studies were conducted on fluoride's effects on the dopamine receptor with morphine, hospitals could use this to help patients with withdrawals and even newborn babies who are born addicted to opioids.

In the last 50 years, the human male sperm count has decreased by half (Wilkinson). Interestingly, fluoridation has been regulated since the 1960s. A correlation between sperm count and fluoride in humans could be made as seen through studies on mice that concluded that the male reproductive system was damaged by lessening sperm count and increasing sperm malfunction ratio (“Fluoride Exposure Changed the Structure and the Expressions of Y Chromosome Related Genes in Testes of Mice”). While this is just speculation, more evidence would need to be collected to find a statistically significant association between fluoride and the sperm count decrease.

The body’s natural sleep patterns are also negatively impacted. Fluoride accumulates freely in the pineal gland, which is responsible for producing melatonin, a hormone related to setting the rhythms and duration of sleep. Thus, fluoride could result in the disturbance of circadian rhythms and sleep patterns (Nakamoto and Rawls). Animals excreted less melatonin metabolite in their urine and took a shorter time to reach puberty also when exposed to fluoride. When 11 human corpses were analyzed, it was found that fluoride in the apatite crystals in the pineal gland averaged about 9000 ppm. Based on this, fluoride is likely to cause decreased melatonin production as well as other effects. A study on the association of fluoride exposure with sleep patterns among adolescents living in the USA shows that fluoride exposure may be a risk factor for sleep disturbances and found that for “each 0.52 mg/L increase in tap water fluoride concentration was associated with 1.97 times higher odds of participants reporting snorting, gasping, or stopping breathing while sleeping at night” (Strunecka and Strunecky).

Fluoride is not just in water; it's in food, drinks, toothpaste, and drugs. Fluoride concentration stood out in almonds with around 3.70 mg/kg, walnuts with 3.50 mg/kg, bread with 2.54 mg/kg, and rice with 2.28 mg/kg. Consumption of 8.32 oz of bread or 1⅓ cups of rice represents the total amount of the recommended daily intake set at 0.6 mg/day for children that are 1 to 3 years of age (Jaudenes et al.). Dried herbs contain up to 2.0 mg of fluoride. Based upon animal and human studies, Chan et al. have found that the presence of fluoride would remain longer due to the ingestion of caffeine-containing beverages. This means that the negative effects of fluoride on bone and brain are prolonged in the presence of caffeine. Scientists have also found that higher fluorosis severity was associated with the consumption of soft drinks that contain caffeine. The tea plant is a natural accumulator of fluoride from the soil, and decaffeinated tea contains more fluoride than caffeinated tea (Nakamoto and Rawls). Trying to rule out fluoride completely from your diet is impossible; however, limiting your intake could be beneficial based on the studies above that have shown the side effects. Especially for pregnant mothers, as they receive as much fluoride as the mother does and yet have a completely different mass and are still developing. Reversing fluoridation is one of the steps needed to protect the future generations of infants.

Community water fluoridation (CWF) is recognized by the government as one of the most cost-effective and safe methods to widely prevent cavities and improve oral health. Thousands of studies showed that CWF prevents cavities and saves money. To support the CWF decision, an economic review by the CDC found that savings for communities ranged from $1.10 to $135 for every $1 invested in fluoridation. However, there are significant costs concerning dental and skeletal fluorosis, hypothyroidism, and mental and cognitive disturbances that the CDC fails to account for in their review. Published in 2016, Hirzy et al. explains that the economic impact of IQ loss among U.S. children is the loss of tens of billions of dollars (Hirzy et al.). In addition, since fluoride has been associated with autism, the annual societal costs for children with ASD were estimated between $11.5–60.9 billion in the USA in 2011, which includes medical care, special education, and lost parental productivity. Additionally, if the increasing rate of ASD prevalence continues, costs could reach nearly $15 trillion by 2029 [174] (Strunecka and Strunecky). Hypothyroidism, lowered fertility rates, and modification of hormonal pathways are also effects of fluoride that account for a lot of money. Beyond just costs, health in itself is important. Using fluoride should be a choice for people around the globe after they’ve examined the benefits and harms. Scientists who believe in this choice and believe in getting more evidence to help the public make this decision are shunned. Bias and blind spots in old beliefs hinder the global population. To add, this same occurrence has happened before, as “it took two decades of research before the CDC declared, ‘There is no safe level of lead in children’s blood… The critics—who were often paid by industry or simply ignorant about lead toxicity but still willing to offer their ‘expert’ opinion—delayed efforts to prevent lead poisoning by decades” (“Controversy: The Evolving Science of Fluoride”). The U.S. public should push for more fluoride research to either confirm existing beliefs that fluoride is completely safe like many scientists say or prove that fluoride is harmful to the body even if it means admitting to a mistake that’s poisoning children, but simply shutting down scientists who push for more fluoride research is unacceptable.

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