Taking a Fresh Look at British Study on Fluoride in Water

Posted November 07, 2023 & filed under Facts about Fluoride, Fluoride and Public Health, Fluoride in the News.

In recent years, multiple studies have compared communities with and without the preventive health benefits of fluoride in water. Each one of these studies has revealed fluoridation’s benefits, but let’s take a closer look at the most recent study, which was conducted in England.

The purpose of CATFISH (Cumbrian Assessment of Teeth a Fluoride Intervention Study for Health) was to examine whether children in fluoridated areas of northern England had less decay than those living in non-fluoridated areas. The CATFISH study determined that children in the fluoridated areas had lower rates of tooth decay.

Yet, as one dental website observed, CATFISH offered “comparatively lukewarm conclusions” about fluoridation. In its story, the Guardian newspaper reported that the study showed that fluoridation “brings smaller benefits to children’s teeth than previously suggested.” However, a new commentary in the British Dental Journal pushes back on these interpretations.

The authors of this commentary contend that a careful analysis of CATFISH shows that fluoridation provided impressive benefits. They explain that the differences between the fluoridated and non-fluoridated groups were downplayed because CATFISH reported the absolute difference, rather than the preventive fraction (PF). Here’s an example:

• If a public health strategy lowered a particular type of hospital admission from a rate of 20% to 15%, the absolute decline would be 5%.
• But calculating the PF (which is how researchers often measure this kind of change) shows a drop of 25% from the original rate of hospital admissions.

How would this change the interpretation of the study? The authors reported that the two cohorts of children in the fluoridated area had a decay prevalence that was 4% and 3% lower. However, if the differences are expressed as the PF, the differences are about 19% and 13% in the two groups. As the commentary notes, “These PF percentages cast the outcome in a new light.”

The authors also point out that one water plant in the supposedly fluoridated area had to stop providing optimal fluoride for about a year. Without this disruption, the differences in the amount of decay might have been greater.

The primary purpose of the CATFISH study was to monitor changes in the prevalence of decay. However, the authors contend that the study largely overlooked a major difference in the extent of decay. Children where there was fluoride in water were 36% less likely to suffer from rampant tooth decay (4 or more decayed teeth) than children who lacked fluoridated water.

The commentary summarizes findings from recent studies in three other nations (U.S., Canada and Israel). These demonstrated that children’s decay rates or dental treatment costs rose significantly after a city or state ceased water fluoridation.