WASHINGTON — The U.S. Environmental Protection Agency’s standard for the maximum amount of fluoride allowed in drinking water — 4 milligrams of fluoride per liter of water — does not protect against adverse health effects, says a new report from the National Academies’ National Research Council. According to the most recent data, just over 200,000 Americans have drinking water sources containing fluoride levels at 4 mg/L or higher. The committee that wrote the report concluded that children exposed to the current maximum allowable concentration risk developing severe tooth enamel fluorosis, a condition characterized by discoloration, enamel loss, and pitting of the teeth. A majority of the committee also concluded that people who consume water containing that much fluoride over a lifetime are likely at increased risk for bone fractures.
The report does not examine the health risks or benefits of the artificially fluoridated water that millions of Americans drink, which contains 0.7 to 1.2 mg/L of fluoride. Although many municipalities add fluoride to drinking water for dental health purposes, certain communities’ water supplies or individual wells contain higher amounts of naturally occurring fluoride; industrial pollution can also contribute to fluoride levels in water. Because high amounts of fluoride can be toxic, EPA places a cap, or maximum contaminant level, on fluoride concentrations in drinking water in order to prevent adverse health effects.
Although the agency’s current maximum contaminant level for fluoride in drinking water is 4 mg/L, a so-called secondary level of 2 mg/L was set by EPA to protect against cosmetic dental effects linked to excess fluoride consumption. According to the most recent data, about 1.4 million people have water with 2 mg/L of fluoride.
In 1993 the Research Council reviewed EPA’s maximum contaminant level for fluoride and found it to be an appropriate interim standard until further research was completed. Now that several more studies have been done and because the Safe Drinking Water Act requires periodic reassessment of regulations, EPA asked for a new review.
Most exposure to fluoride in the United States results from consumption of water and water-based beverages, but dental products, food, and other sources contribute as well. Highly exposed subpopulations include individuals who have high concentrations of fluoride in their drinking water or who drink more water than the average person because of exercise, outdoor work, or a medical condition. Relative to their body weight, infants and young children are exposed to three to four times as much fluoride as adults. Children also may use more toothpaste than is advised or swallow it, and many receive fluoride treatments from their dentists. Fluoride accumulates in bone over time, so groups likely to have increased bone fluoride concentrations include the elderly and people with severe renal deficiency who have trouble excreting fluoride in their urine.
When assessing the risk for adverse health effects in populations with water fluoride concentrations near the level of the EPA standards, the committee assumed these populations had the same exposure to other sources of fluoride as populations with smaller amounts of fluoride in their water.
On average, approximately 10 percent of children in communities with water fluoride concentrations at or near 4 mg/L develop severe tooth enamel fluorosis, the new report says. Previous assessments have considered all cases of enamel fluorosis, including serious ones, to be aesthetically displeasing because of the yellow and brown staining of teeth that occurs, but not adverse to health. However, the committee said that severe cases of enamel loss constitute an adverse health effect because one function of enamel is to protect the teeth and underlying dental tissue from decay and infection. “The damage to teeth caused by severe enamel fluorosis is a toxic effect that is consistent with prevailing risk assessment definitions of adverse health effects,” the committee reported. Two of the 12 committee members did not agree that enamel defects alone are sufficient to consider severe enamel fluorosis an adverse health effect as opposed to a cosmetic one, but they did agree that EPA’s maximum contaminant level goal should be lowered to prevent the occurrence of this unwanted condition.
Earlier studies indicate that up to 15 percent of children in communities with 2 mg of fluoride per liter of water have moderate tooth enamel fluorosis. Although this condition can also lead to tooth discoloration that may be aesthetically objectionable, there is inadequate data to categorize it as an adverse health effect.
Several studies indicate an increased risk of bone fracture in populations exposed to fluoride concentrations in water of 4 mg/L or higher, the committee added. Although fluoride increases bone density as it accumulates in bone, there is evidence that under certain conditions it can weaken bone and increase the risk of fractures. Most of the committee concluded that a population with lifetime exposure to fluoride in water at concentrations of 4 mg/L or higher is likely to experience more fractures than a group exposed to 1 mg/L. Three of the 12 committee members, however, only supported a conclusion that EPA’s 4 mg/L limit might not be protective against bone fractures; they said more evidence was needed before drawing a conclusion that increased risk of fracture is likely. There was insufficient data for the committee to reach any conclusions about fracture risk at the 2 mg/L level.
The report also looks at the risk of skeletal fluorosis, a bone and joint condition associated with prolonged exposure to high concentrations of fluoride. The most severe stage of skeletal fluorosis appears to be rare in the United States, the committee noted. It also said that it could not determine if earlier stages of the disease are occurring in U.S. residents who drink water with fluoride at the 4 mg/L level, and that more research is needed in this area.
The evidence to date regarding fluoride’s potential to cause cancer, particularly of the bone, is tentative and mixed, the committee added. A study under way at the Harvard School of Dental Medicine, expected to be published this summer, may help identify future research that would be useful for studying fluoride’s carcinogenic potential.
The committee’s study was sponsored by the U.S. Environmental Protection Agency. The National Research Council is the principal operating arm of the National Academy of Sciences and the National Academy of Engineering. It is a private, nonprofit institution that provides science and technology advice under a congressional charter.