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.