Washington ? The high levels of fluoride that occur naturally in some drinking water can cause tooth and bone damage and should be reduced, the National Research Council said Wednesday.

The study did not analyze the benefits or risks of adding fluoride to drinking water. Instead it looked at the current maximum limit of 4 milligrams per liter. Approximately 200,000 people live in communities where that level occurs naturally in water.

The Council suggested further studies to establish a new maximum level, but noted that the problems associated with exposure to fluoride are very small at 2 milligrams per liter and less. Approximately 1.4 million people have drinking water with natural fluoride levels of 2.0 to 3.9 milligrams per liter, said the Council, an arm of the National Academy of Sciences.

More than 160 million Americans live in communities with artificially fluoridated water, which contains between 0.7 and 1.2 milligrams of fluoride per liter.