A new Duke University-led study looked at fluoride in the groundwater in the Main Rift Valley of Ethiopia, where as many as 8 million people depend.

They discovered that the residents are at high-risk of dental and skeletal fluorosis as a result of their long-term exposure to high levels of naturally occurring fluoride in the region’s groundwater, according to duke.edu.

By analyzing the groundwater quality in the valley, the study found that as water flows from the surrounding mountains into the valley, where it interacts with volcanic rock, which in turn adds high levels fluoride to the water while also removing most of its calcium.

High levels of fluoride can contribute to tooth decay and dental fluorosis, particularly in children between the ages of 3 months and 8 years.

The new Duke-led study, published online in the journal Environment International (www.sciencedirect.com/science/article/pii/S0160412012000530), finds that these efforts “may not be sufficient on their own, because of the region’s geology and the low threshold of exposure at which we found fluorosis was likely to occur,” said Avner Vengosh, professor of geochemistry and water quality at Duke’s Nicholas School of the Environment.

Increasing the amount of calcium in villagers’ diets, or finding alternative sources of drinking water may be necessary in addition to these fluoride-reducing treatments.

Water samples from 48 of 50 wells tested in the Main Rift Valley contained fluoride levels six times higher than the World Health Organization safe guidelines of 0.5 to 1.5 mg/litre (milligrams per liter, equivalent to parts per million). The U.S. optimal level of fluoride in drinking water ranges from 0.7 to 1.2 mg/litre.

In some of the communities in the valley, the fluoride levels in their well water were so high that treating the water to cut the fluoride content by half didn’t drop the fluoride levels below the guidelines.

According to the report, most efforts to combat fluorosis in the Main Rift Valley have focused primarily on treating drinking water to reduce its fluoride content.

However, in villages where people had access to milk, the researchers found that severe fluorosis was about 10 percent less likely to occur. Further research is needed to explain this exception, but it may be possible that by injesting milk some of the population received enough calcium to hinder fluorosis development.

An increase in calcium may be key to addressing widespread oral health problems faced by the millions of rural residents in Ethiopia’s remote, poverty-stricken Main Rift Valley.

For more on this story see: Water Treatments Alone Not Enough to Combat Fluorosis in Ethiopia