Fluoride toxicity

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Fluoride toxicity is a condition in which there are elevated levels of the

In India an estimated 60 million people have been poisoned by well water contaminated by excessive fluoride, which is dissolved from the granite rocks. The effects are particularly evident in the bone deformities of children. Similar or larger problems are anticipated in other countries including China, Uzbekistan, and Ethiopia.^[5]

Acute

Historically, most cases of acute fluoride toxicity have followed accidental ingestion of sodium fluoride based

Children may experience gastrointestinal distress upon ingesting excessive amounts of flavored toothpaste. Between 1990 and 1994, over 628 people, mostly children, were treated after ingesting too much fluoride-containing toothpaste. "While the outcomes were generally not serious," gastrointestinal symptoms appear to be the most common problem reported.[15] However given the low concentration of fluoride present in dental products, this is potentially due to consumption of other major components.

Fluoride in drinking water

Around one-third of the world's population drinks water from groundwater resources. Of this, about 10 percent, approximately 300 million people, obtains water from groundwater resources that are heavily contaminated with arsenic or fluoride.^[16] These trace elements derive mainly from leaching of minerals.^[17] Maps are available for locations of potential problematic wells via the Groundwater Assessment Platform (GAP).^[18]

Effects

Excess fluoride consumption has been studied as a factor in the following:

Brain

Some research has suggested that high levels of fluoride exposure may adversely affect

Whilst fluoridated water is associated with decreased levels of fractures in a population,

Consumption of fluoride at levels beyond those used in fluoridated water for a long period of time causes skeletal fluorosis. In some areas, particularly the Asian subcontinent, skeletal fluorosis is endemic. It is known to cause irritable-bowel symptoms and joint pain. Early stages are not clinically obvious, and may be misdiagnosed as (seronegative) rheumatoid arthritis or ankylosing spondylitis.^[22]

Kidney

Fluoride induced nephrotoxicity is kidney injury due to toxic levels of serum fluoride, commonly due to release of fluoride from fluorine-containing drugs, such as methoxyflurane.^[23][24][25]

Within the recommended dose, no effects are expected, but chronic ingestion in excess of 12 mg/day are expected to cause adverse effects, and an intake that high is possible when fluoride levels are around 4 mg/L.^[21]: 281 Those with impaired kidney function are more susceptible to adverse effects.^[21]: 292

The kidney injury is characterised by failure to concentrate

Elimination of fluoride depends on glomerular filtration rate. Thus, patients with chronic kidney disease will maintain serum fluoride for longer period of time, leading to increased risk of fluoride induced nephrotoxicity.

Teeth

The only generally accepted adverse effect of fluoride at levels used for water fluoridation is dental fluorosis, which can alter the appearance of children's teeth during tooth development; this is mostly mild and usually only an aesthetic concern. Compared to unfluoridated water, fluoridation to 1 mg/L is estimated to cause fluorosis in one of every 6 people (range 4–21), and to cause fluorosis of aesthetic concern in one of every 22 people (range 13.6–∞).^[20]

Thyroid

Fluoride's suppressive effect on the thyroid is more severe when iodine is deficient, and fluoride is associated with lower levels of iodine.^{[clarification needed][29]} Thyroid effects in humans were associated with fluoride levels 0.05–0.13 mg/kg/day when iodine intake was adequate and 0.01–0.03 mg/kg/day when iodine intake was inadequate.^[21]: 263 Its mechanisms and effects on the endocrine system remain unclear.^[21]: 266

Testing on mice shows that the medication

Fluoride accumulates in the bone tissues of fish and in the exoskeleton of aquatic invertebrates. The mechanism of fluoride toxicity in aquatic organisms is believed to involve the action of fluoride ions as enzymatic poisons. In soft waters with low ionic content, invertebrates and fishes may develop adverse effects from fluoride concentration as low as 0.5 mg/L. Negative effects are less in hard waters and seawaters, as the bioavailability of fluoride ions is reduced with increasing water hardness^[31] Seawater contains fluoride at a concentration of 1.3 mg/L.^[32]

Mechanism

Like most soluble materials, fluoride compounds are readily absorbed by the stomach and intestines, and excreted through the urine. Urine tests have been used to ascertain rates of excretion in order to set upper limits in exposure to fluoride compounds and associated detrimental health effects.^[33] Ingested fluoride initially acts locally on the intestinal mucosa, where it forms hydrofluoric acid in the stomach.

References