Q & A Library

No, I have not changed my views about fluoride. Its addition to most public water supplies is credited with a 40 to 60 percent reduction in tooth decay in children and adults. Fluoride not only helps prevent tooth decay and cavities, it promotes strong teeth and enamel.

I have always maintained, however, that fluoride isn't risk-free. Excessive amounts can create chalky white, irregular patches on the surface of teeth, causing the enamel to appear mottled. In very large amounts, fluoride is toxic. It can cause gastrointestinal problems and, rarely, death. Signs of fluoride overdose include excessive salivation, tremors, weakness, convulsion and a soapy or salty taste in the mouth. While high amounts of fluoride over several years can cause brittle bones, this is extremely rare.

As far as bone cancer is concerned, every year about 400 children and adolescents (boys and girls) in the U.S. are diagnosed with osteosarcoma, a rare disease. In 2006, Harvard researchers reported an association between fluoride in drinking water and the incidence of osteosarcoma in boys (not girls). A preliminary analysis of a second set of cases doesn't appear to support the earlier observed connection between fluoride in drinking water and osteosarcoma in young boys, according to the U.S. Centers for Disease Control and Prevention.

Furthermore, the CDC concluded that analysis and reviews of earlier studies of water fluoridation and osteosarcoma don't support an association between the two. This case isn't closed - more research is in progress, but so far, we have no hard evidence demonstrating that fluoride causes or promotes bone cancer.

As far as dogs are concerned, a study by the Environmental Working Group (EWG), a Washington, D.C.-based consumer protection organization, found that eight major national brands of dog and puppy food contained fluoride in amounts between 1.6 and 2.5 times higher than the Environmental Protection Agency's maximum legal dose in drinking water and higher than amounts associated with bone cancer in young boys in the study mentioned above. All eight brands contained bone meal and animal byproducts, which is probably where the fluoride came from.

According to the EWG data, some 8,000 dogs in the United States are diagnosed with osteosarcoma each year compared to only 900 human cases (500 adult cases in addition to the 400 children). However, we simply don't know whether the fluoride in dog food or drinking water accounts for the osteosarcoma some animals develop. If you're concerned about any potential risk to your pets, avoid buying dog food containing animal byproducts. Regardless of the osteosarcoma risk, I strongly recommend this for the health of your pets in general. When choosing food for my own dogs I stay away from anything containing animal byproducts, rendered or recycled meats, poultry or fats. Avoid animal based "meals" (for example, "chicken meal") and look for quality meat or fish protein as first ingredients.

Andrew Weil, M.D.