Study Review Yields Doubt on Fluoridated Water’s Effectiveness

Image courtesy of Idea go at


Image courtesy of Idea go at

The United States has been adding fluoride to its drinking water since 1945, as many authorities consider it an essential strategy in fighting tooth decay. But researchers from the Cochrane Oral Health Group have reason to question its effectiveness.

The organization examined 155 previous studies published through February of this year comparing children receiving fluoridated water to those receiving water with little or no fluoride.

The initial data suggests that water fluoridation reduced decayed, missing, of filled baby teeth by 35% and decayed, missing, or filled permanent teeth by 26%. It also increased the percentage of children with no decay by 15%. These results indicate that water fluoridation is effective at reducing levels of tooth decay in children’s baby and permanent teeth.

However, the researchers say that the applicability of these results to current lifestyles is unclear because most of these studies were conducted before fluoride toothpastes and other preventative measures were widely used in many communities around the world. In fact, of the 20 studies that studied tooth decay, 71% were conducted prior to 1975.

Additionally, the researchers say there was insufficient information available to find out whether the introduction of a water fluoridation program changed existing differences in tooth decay across socioeconomic groups. They also say there was insufficient information available to understand the effect of stopping water fluoridation programs on tooth decay. And, none of the studies met the review’s inclusion criteria that investigated the effectiveness of water fluoridation for preventing tooth decay in adults, rather than children.

Furthermore, the review authors assessed each study included in the review for risk of bias by examining the quality of the methods used and how thoroughly the results were reported to determine the extent to which the results reported were likely to be reliable. The assessment showed that more than 97% of the 155 studies were at high risk of bias, reducing the overall quality of the results. There was substantial variation between studies in terms of results as well.


The researchers drew these studies from seven different electronic databases. They also searched the US National Institutes of Health Trials Registry ( and the World Health Organization’s WHO International Clinical Trials Registry Platform for ongoing trials. There were no restrictions on language of the publication or publication status in the searches of the electronic databases.

For caries data, the researchers only included prospective studies with a concurrent control that compared at least two populations, one receiving fluoridated water and the other non-fluoridated water, with outcomes evaluated at least at two points in time. For the assessment of fluorosis, they included any type of study design with concurrent control that compared populations exposed to different water fluoride concentrations. They included populations of all ages that received fluoridated water, naturally or artificially fluoridated, or non-fluoridated water.

As for caries indices, the researchers included decayed, missing, and filled teeth (dmft [deciduous dentition] and DMFT [permanent dentition]) and proportion caries free in both dentitions. For dmft and DMFT analyses, they calculated the difference in mean change scores between the fluoridated and control groups.

For the proportion caries free, they calculated the difference in the proportion caries free between the fluoridated and the control groups. For fluorosis data, they calculated the log odds and presented them as probabilities for interpretation.

The study was conducted by Zipporah Iheozor-Ejiofor, Helen Worthington, Tanya Walsh, Lucy O’Malley, Jan E. Clarkson, Richard Macey, Rahul Alam, Peter Tugwell, Vivian Welch, and Anne-Marie Glenny. The full report is available from the Wiley Online Library.