Of the 30 largest cities in America, Portland, OR is the only one to repeatedly resist fluoridating their drinking water. Opponents cite studies that claim it lowers IQ in developing children. Supporters argue it is the safest and most beneficial addition to modern healthcare in the last 100 years. It's no question that fluoride has an important link to dental health -- too little can lead to tooth decay and too much can harbor dental fluorosis in children. When it comes to fluoridation, how much is too much?

According to the CDC, the recommended fluoride level in drinking water for good oral health is 0.7 milligrams per liter. But since fluoride occurs naturally in some water supplies, the amount you are drinking may vary widely. If your home is served by a water system that has fluoride levels exceeding 4 mg/L, the EPA recommends that children especially should be provided with alternative sources of drinking water.

The EPA also warns that exposure to excessive consumption of fluoride over a lifetime may lead to increased likelihood of bone fractures in adults, and may result in chronic pain or 'tenderness'. But with all medicines, the dosage defines the poison. Because fluoride has been rigorously tested and implemented for over 65 years, supporters say these side effects are negligible and the benefits to dental health outweigh the costs.

Water fluoridation evens the rate of tooth decay in impoverished communities with little access to dental care. A recent study found that 42 percent of low-income students had untreated tooth decay compared with just 20 percent for high-income students. But is mass dosing the population whether they want to consume fluoride or not treating the cause of this problem, or merely a symptom? Opponents argue there are better ways to ramp up dental health for the impoverished through education, healthcare reform and access to wholesome, healthy food.

And though the aforementioned study on reduced IQ linked to fluoride exposure was thoroughly refuted because it was conducted in China with naturally occurring fluoride levels reaching 10 mg/L, the fact that about 90 percent of the fluoride added to public water supplies comes from chemicals produced as byproducts from the manufacture of phosphate fertilizers still makes people uneasy.

The bottom line is this. The science widely supports a healthy amount of fluoride in the water supply, with estimates that every dollar invested in fluoridation saves another $38 in annual dental healthcare costs. Those at greatest risk of dental fluorosis or adverse reactions to unhealthy levels of fluoride are young children. If fluoridation concerns you test or research the drinking water in your community, and take the necessary actions to do what feels healthy and safe for you and your family.