Knowledge Precedes Policy: An examination of changing beliefs in the scientific and medical communities regarding water fluoridation

Abstract

Artificial fluoridation of water supplies has been a common practice for over fifty years. The justification for fluoridating community water supplies has become so ingrained in collective thought that few members of the public would challenge the idea of adding fluoride to drinking water. However, in the last ten years there has been a notable change in thinking regarding systemic ingestion of fluoride. While previously the challenges have come from outside science and medical fields, and been based on free choice, the newest challenges are coming from within the field of dentistry itself. Resistance to changing the policies of fluoridating water is strongest from public health officials, who were previously reluctant to fluoridate. The change in thinking highlights several aspects to the study of toxicology, most notably that the advancement of scientific and medical knowledge first drove the adoption of fluoridating water sources and is now driving the challenges to fluoridating water.

Detection of Bias

There is a notable disparity of attitudes towards community water fluoridation (CWF) between North American and European countries. Particularly, there seemed to be a bias in the United States towards justification of CWF based on cost-effectiveness towards reducing caries (cavities), while in Europe there appears to be a bias towards health effects and alternatives to CWF through topical application. In some cases, both perspectives would refer to the same research but indicate justification consistent with the perspective.

Large Scale Reviews From Both Sides of Atlantic Ocean Indicate Lack of Quality In Research

In recent years two large-scale reviews (NRC 2006, McDonagh et al. 2000) have been undertaken to examine publications and data regarding effects of fluoride. The National Research Council review was wider in scope and included non-dental issues. McDonagh et al., also known as the “York Review” in literature, was limited to evaluating dental issues. Both reviews consistently identified a lack of quality in methodology. This has worked in both directions, where evidence supporting benefits of fluoridated water has not been beyond question, and evidence supporting links to other conditions such as cancer and Down’s Syndrome have not been categorically supported, either. Certain conditions, such as fluorosis, are well documented, while other conditions, such as altered endocrine response, impaired neurologic function and unnaturally increased bone density are highly indicated but not definitive. The reviews both concluded that additional research with higher quality methodology is essential.

A third review (Pizzo, Piscopo, Pizzo, and Giulianna 2007) was also examined. Pizzo et al. did not review the quality of the data collection or determination of conclusions, and generally balanced both viewpoints.

Exposure Limits

Current Environmental Protection Agency (EPA) maximum contaminant level goals (MCLG) for fluoride are 4 ppm, but the EPA has also established a secondary maximum contaminant level (SMCL) of 2 ppm for issues regarding cosmetics and aesthetics (NRC 2006). Although fluorine is recognized as a poison and fatal doses of fluoride to young children can be obtained from toothpaste, water fluoridation levels do not normally incur mortality or acute illness.

Fluoride Beneficial...To a Point

The local drinking water was identified by Frederick McKay as the main factor to the discoloration of teeth being exhibited by residents of Colorado Strings, Colorado. The same residents also displayed substantial resistance to caries (Pizzo, et al. 2007). Subsequent studies showed that the component in the drinking water was fluoride, and that it works to prevent caries by aiding remineralization of the enamel coating on teeth. Bacteria causes demineralization of the enamel, and feed on the sugars produced from the decay of food. Caries result from the demineralization rate exceeding the remineralization rate. The mechanism by which fluoride assists in remineralization is well-documented (Featherstone 2000).

In the United States the primary source of artificially introduced fluoride is in the form of fluorosilicates, from the manufacture of phosphate fertilizers (NRC 2006). Fluoride occurs naturally as sodium fluoride, found in many salts and rock formations, and as a result many natural water sources have fluoride levels of 2-4 ppm or higher (Masters and Copland 1999). Typically, suppliers of artificially fluoridated water use a range of 0.8 to 1.3 ppm as a guideline (NRC 2006).

Many current studies on the effects of fluoridation refer to the work of Heller, Ecklund and Burt (1997) for incidence rates. The lowest observable effects for the prevention of caries is approximately 0.3 ppm. Optimal levels at which fluoride needs to be present for remineralization is approximately 0.7 ppm, as levels above this do not return appreciably better protections (Heller, Ecklund, and Burt 1997). Benefits occur when applied topically or systemically (Cheng, Chalmers and Sheldon 2007). Water fluoridation uses ingestion for systemic introduction of fluoride. The addition of fluoride to many products such as mouthwash, cough drops, and toothpaste in conjunction with fluoridated water raises the exposure levels even more but has not been shown to have additive effects reducing caries at levels beyond 1.3 ppm (Heller et al. 1997, Pizzo et al. 2007). Featherstone (2000) states that studies of comparisons of pre- and post-eruptive conditions refute previous beliefs that fluoride was essential during the formation of the teeth and show benefits are almost exclusively topical.

The addition of fluoride to community water has been shown to correspond to significant drops in rates of caries in those communities (Heller et al. 1997). However, similar rates of caries in non-fluoridated communities have also been detected (Cheng et al. 2007). Questions regarding the correlation between fluoridation and decreased caries are being raised, and critics are pointing to increased dietary nutrition and increased knowledge about dental hygiene as being the significant factors in the decrease in rates of caries (Pizzo et al. 2007).

After the Point of Benefits, Issues Are Serious

Chronic ingestion of fluoride above 1 ppm in water or 1 mg/kg body weight has been linked to many damaging conditions. Fluorosis, a condition in which the enamel has become permanently discolored, occurs at levels within possible exposure rates. Heller et al. (1997) identified an increase of both prevalence and severity of fluorosis with increasing fluoridation levels above 0.7 ppm, to a level twice that of rates below 0.3 ppm. The NRC review (2006) found that limiting fluoride levels to 4 ppm did not prevent severe fluorosis and presented research that found decreased levels of fluorosis below 2 ppm. The range seems clear, in that exposure to levels less than twice the beneficial level begin to incur negative impacts.

The same mechanism that causes fluorosis has been identified as increasing bone density (NRC 2006), leading to increased risks of skeletal fluorosis, a crippling and painful disease. The NRC review found that studies suggested current MCLG limits of 4 ppm are too high and unlikely to be protective.

Fluoride has also been linked to an interruption of proper thyroid function. One benchmark for identifying thyroid impairment has been the measure of goiter, the severe swelling of the thyroid gland. Jooste, Kreik, Weight, and Louw (1999) studied goiter rates in six towns in South Africa where the participants have lived in the same town their entire life. Fluoride levels ranged from 0.5 ppm to 2.6 ppm, ranges found in both natural and artificially fluoridated water supplies in North America. Jooste et al. noted the correlation between fluoride levels and goiter rates, but did not conclude fluoride was a goitrogen. The EPA review (2006) took data from Jooste et al. and demonstrated a nearly linear relationship between fluoride levels and goiter. The single exception to the near-linear relationship was a town that had substantially lower rates of undernutrition, and the goiter rates were also substantially below the other towns. Iodine levels were not available for that town.

The EPA review also noted that Day and Powell-Jackson (1972) showed a clear correlation between drinking water fluoride levels and goiter rates in the absence of iodine in villages in Nepal, Here as well, the authors did not draw direct causal connections that re-examination by the NRC review highlighted. The NRC review (2006) referenced one study (Susheela et al. 2005) that indicated in the presence of high levels of fluoride, proper levels of iodine is not sufficient to offset thyroid impairment. Although not definitive, there appears to be some basis to conclude that undernutrition and high rates of fluoride ingestion work additively to affect thyroid behavior, while proper nutrition works antagonistically, to a point.

Neurological impairment may occur in conjunction with high fluoride levels. The NRC review (2006) referred to several studies in China that indicated reduced IQ levels and asymmetric IQ distributions with bias towards low scores, but determined that the studies did not release sufficient data and information regarding methodology to enable independent review. However, the NRC review specifically pointed to the consistency of the results to suggest additional research into this aspect should be undertaken. This impairment is not identifiable at fluoride levels within suggested guidelines for artificial fluoridation, but is identifiable at levels found in naturally occurring water sources. The NRC review (2006) noted that reduced intellectual development can be caused by thyroid impairment.

Although not in the same form as used in CWF (typically fluorosilicates), fluorine is also a major component to the antidepressant fluoxetine, which is marketed as Prozac. The ability of fluorine to be used as a selective serotonin uptake reinhibitor (SSRI) should not be ignored when considering neurological impacts of fluoride.

Recent studies have shown that fluoride may act synergistically in the uptake of lead (Masters and Copland 1999). Masters and Copland (1999) identify the form that fluoride is introduced to the water supply as particularly associated with elevated lead levels in water supplies. Lead poses a particular problem. Communities with low incomes are at risk for high rates of caries, but those same communities also have older infrastructures with higher rates of lead in fixtures (brass) and connections (lead solder), as well as older homes that may contain lead paint. Many communities are changing to using chloramine (which adds ammonia to chlorine) in the water due to its stability, but chloramine has also been linked to increased leeching of lead (Switzer, Rajasekharan, Boonsalee, Kulp, and Bohannan. 2006). The combination of chloramine and fluoride in water supplies potentially acts additively to increase lead levels in drinking water, and the fluoride may substantially increase the uptake of that lead into developing brains. The effects of introducing multiple contaminants into a single source are difficult to determine but rarely beneficial.

Ethical Questions About Community Water Fluoridation Projects

Proponents of CWF repeatedly connect two points, that fluoride occurs naturally in many water supplies, and fluoride has been shown to be a cost-effective approach to reducing caries. Proponents explain that CWF simply makes municipal water systems achieve the same level of fluoridation as naturally occurring sources that have been shown to be beneficial. Featherstone (2000) emphasizes that caries are caused by the presence of bacteria and is a disease to be treated with medication. Since the purpose of fluoridation is to reduce incidence of a disease, opponents of CWF state fluoridation is a medication which must adhere to medical oversight requirements and guarantee the individual the right of consent. Medically, the intent is to use the least amount of medication to achieve the desired result, and opponents to CWF point to the effectiveness of topical applications as offering an alternative to systemic ingestion of fluoride.

Conclusions

The association of fluoride with the prevention of tooth decay has been used to justify the addition of fluoride to drinking water and a wide range of other products. However, the benefits from fluoride are also achieved when applied topically, and systemic ingestion of fluoride is being linking to a large number of disorders, from discolored teeth to altered thyroid function. Negative impacts occur within levels seen from cumulative exposure to allowable limits. Negative impacts are most closely associated with low nutrition intake primarily and low quality infrastructure secondarily. Both conditions are more prevalent in the very target communities for community water flouridation.

Efforts should be made to inform consumers about the appropriate levels and methods of fluoride exposure. Consistent evidence points to negative impacts at levels as low as twice beneficial levels. Ethical issues exist regarding consent and determination of fluoridation as a medicine. Growing evidence suggests that our exposure level to fluoride is too high, possibly leading to synergistic effects between fluoride and lead, aluminum and mercury uptake.

A resolution would appear to be to devote more resources in underdeveloped and developing countries towards increasing dietary nutritional content for all ages and the distribution of affordable fluoridated toothpaste to individuals capable of applying toothpaste without ingestion.

These beliefs are being increasingly promoted in the science and medical communities. Previously the science and medical communities had promoted water fluoridation. Policy changes followed previous beliefs, and policy changes may follow current beliefs.