Systematic Reviews: Assessing the Weight of the Evidence

An important resource used to assess the safety of a health care strategy such as water fluoridation are systematic reviews of scientific literature. Systematic reviews are helpful because they:

• Seek to collect evidence from all published studies on a subject.
• Use carefully-designed methods to critically examine scientific evidence.
• Use national and international panels of experts in various health and scientific disciplines, including many experts outside of oral health, including medicine, biophysics, chemistry, toxicological pathology, and epidemiology.
• Assess the quality of individual studies and summarize the strength of the entire body of evidence.
• Summarize information regarding other evidence.
• Identify and summarize research gaps and make recommendations for further research.

Systematic reviews have been conducted by several scientific and public health organizations over the past two decades. All have concluded that community water fluoridation is a safe and effective method for reducing tooth decay across all ages.

United States Public Health Service Review of Fluoride: Benefits and Risks, 1991
Comprehensive review and evaluation of the public health benefits and risks of fluoride from drinking water and other sources.

Institute of Medicine Dietary Reference Guidelines, 1997*
Describes the dietary reference intakes for specific nutrients known to be beneficial to health including fluoride.

National Research Council

The NRC released its current report, Fluoride in Drinking Water: A Scientific Review of EPA’s Standard, on March 22, 2006. The National Research Council's (NRC) previous report, entitled Health Effects of Ingested Fluoride, was issued in 1993. It examined the possible toxic effects of ingested fluoride and concluded:

• Fluoride at recommended concentrations is not likely to produce a number of unwanted health effects that had been claimed by opponents of water fluoridation.
• The maximum contaminant level (MCL) set by the Environmental Protection Agency (EPA) at 4 mg/L was an appropriate interim standard, even though fluoride at this level might cause moderate or even severe dental fluorosis in a small percentage of the population.

The full 1993 report can be found at http://www.nap.edu/books/030904975X/html/R1.html.* 

Australian Government

Australia's National Health and Medical Research Council (NHMRC) conducted a systematic review published in 2007, that considered recent evidence relating to the efficacy and safety of fluoride interventions, with an emphasis on widespread public health initiatives. The report, A Systematic Review of the Efficacy and Safety of Fluoridation, primarily addressed the caries-reducing benefits and associated health risks of providing fluoride systemically. The council found that

• Community water fluoridation is beneficial for reducing dental caries (tooth decay).
   
• Water fluoridation at optimal levels does not affect the risk of bone fractures.
   
• There is no clear association between water fluoridation and overall cancer incidence or mortality.
   
• The reviewed studies do not suggest an increased risk of adverse health effects at optimal fluoridation levels.

View the full report  provided by the Australian Government NHMRC.

NHMRC is Australia's main agency for supporting health and medical research; developing health advice for the Australian community, health professionals and governments; and providing advice on ethical behavior in health care and in the conduct of health and medical research.

University of York

A systematic review of public water fluoridation was released in 2000 by the National Health Service (NHS) Centre for Reviews and Dissemination, University of York, United Kingdom. This looked at the evidence on positive and negative effects of community water fluoridation. They identified five objectives and evaluated the studies relating to each objective. Based on the best available research they found that:

• Community water fluoridation reduces tooth decay.
• Fluoridation is still effective even with the use of many other sources of fluoride.
• There is no clear association between fluoridation and bone fractures or cancer.
• There appears to be no difference between benefits from natural and artificial fluoridation.
• There is an association between the water fluoride concentration and the occurrence of enamel fluorosis.
• No clear evidence of other potential negative health effects were found.

The full report can be found at http://www.york.ac.uk/inst/crd/fluores.htm.*

Additional systematic reviews on the benefits of water fluoridation may be viewed on the Benefits page.

* Links to non-Federal organizations are provided solely as a service to our users. Links do not constitute an endorsement of any organization by CDC or the Federal Government, and none should be inferred. The CDC is not responsible for the content of the individual organization Web pages found at this link.

Date last reviewed: September 26, 2007
Date last updated: August 9, 2007
Content source: Division of Oral Health, National Center for Chronic Disease Prevention and Health Promotion