A similar debate exists in Australia, where some water suppliers have implemented fluoridation in recent years and others ponder whether to move forward with it. Now a group of researchers from the University of North Carolina (UNC) School of Dentistry and the University of Adelaide have entered the debate with a new study on the effectiveness of water fluoridation (Journal of Dental Research, March 1, 2013).
“It benefits everyone living in the city from
— Gary Slade, BDS, DPH, PhD, University
of North Carolina School of Dentistry
Using a nationally representative sample of Australian adults as the source of their data, the researchers concluded that the "caries-preventative effects of water fluoridation were at least as great in adults born before widespread implementation of fluoridation as after widespread implementation of fluoridation."
Adults who spent more than 75% of their lifetime living in a community with water fluoridation had significantly less decay than those who had lived in one for less than 25% of their lifetime, they noted.
"A random sample of an entire national survey has never been done before [in a fluoridation study]," said Gary Slade, BDS, DPH, PhD, a distinguished professor and the director of the oral epidemiology doctoral program at UNC's School of Dentistry, in an interview with DrBicuspid.com. "The U.S. does national dental surveys of decay, but what's not done in the National Health and Nutrition Examination Survey is digging into a lifetime of where people have lived in terms of fluoridated and unfluoridated areas. It's unusual for them to go back to earlier life experiences."
What the researchers ended up with in their examination of the survey is a "guarded conclusion" that fluoride is effective based on a new dimension of evidence.
"We looked at it a few ways, and there are certain assumptions you have to make," Dr. Slade explained. "Not everyone answers the survey questions perfectly, but when we went back and forth in certain assumptions, we kept returning to a noticeable effect of 10% to 30% less decay -- 10% at a population level with even 1 million people is a lot of cavities."
Not just for kids
Fluoridation was previously thought to primarily benefit children who were raised drinking fluoridated water. Consequently, there is sometimes a perception that "it would take us 10 to 15 years to see the benefit of only a 10% reduction" in decay, Dr. Slade noted. That can lead to disagreements about the cost-benefit ratio of fluoridation. This study could alter that discussion.
"[Fluoridation] is not just for kids -- it benefits everyone living in the city from day one," he added. "The benefit was at least as great for people who began living in areas fluoridated after they were born. This is a massive change in the cost-effectiveness ratio right there from what we have traditionally factored in."
The researchers analyzed national survey data from 3,779 adults age 15 and older selected at random from the Australian population between 2004 and 2006. Survey examiners measured levels of decay, and study participants reported where they lived since 1964. The residential histories of study participants were matched to information about fluoride levels in community water supplies. The researchers then determined the percentage of each participant's lifetime in which the public water supply was fluoridated.
"The interesting thing about the survey conducted from 2004 to 2006 was that it captured quite a window of a natural experiment that started in the early '60s," Dr. Slade said. "Australian cities began fluoridating in a space of about 15 years; the percentage increased from about zero to two-thirds of the population living in fluoridated areas by the late 1970s." And while some Australians had spent all of their life in a fluoridated community, many had spent none, allowing for excellent comparative analysis, he added.
With it, along with evidence from other studies, "we believe that the current findings of an inverse association between water fluoridation and caries experience provide reasonable evidence of a causal, preventative effect in Australian adults," the researchers concluded.
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