Community Water Fluoridation Exposure: A Review of Neurological and Cognitive Effects – A 2020 Update [Internet]

Excerpt

In Canada, community water fluoridation (CWF) is the process of monitoring and controlling fluoride levels (by adding or removing fluoride) in the public water supply to reach the optimal level of 0.7 mg/L or part per million (ppm) and not to exceed the maximum concentration of 1.5 ppm, as recommended in the 2010 Health Canada Guidelines for Drinking Water Quality. CWF has been identified as a cost-effective method of delivering fluoride to the population and reducing dental caries in children and adults.^, The Centers for Disease Control and Prevention recognized CWF as one of 10 great public health achievements of the 20^th century because of its contribution to the prevention of tooth decay and improvement in oral health over the past 70 years. CWF is endorsed by over 90 national and international governments and health organizations around the world.^,

Despite the endorsement of governments and health organizations, and a large body of empirical evidence on the preventive effect of CWF on dental caries, a number of municipalities across Canada have not implemented or have discontinued water fluoridation. In 2017, 38.7% of the Canadian population were exposed to community water systems having recommended optimal fluoride levels to protect their teeth. Different factors have contributed to CWF cessation including concerns about the potential harmful side effects of water fluoride to human health, including fluorosis, skeletal fractures, cancer, reproduction and development, thyroid function, and neurological development and cognitive function.

Multiple studies have been published showing that exposure to higher levels of fluoride in drinking water may be associated with lower intelligence among children.^– However, the applicability of the findings from those studies to the Canadian context is unlikely given they were conducted in rural and endemic areas and areas of low socioeconomic status in countries, such as China, India, Iran, or Mexico, which also include other sources of fluoride such as fluoridated salts or naturally occurring water fluoride levels that are many folds higher than the current Canadian levels.^– Multiple methodological limitations were identified in those studies including insufficient control for important confounding factors and low quality study design.^,

The CADTH CWF Review of Dental Caries and Other Health Outcomes reviewed studies from countries with comparable water fluoride levels and socioeconomic parameters, and found no evidence for an association between water fluoridation at recommended Canadian levels and intelligence quotient (IQ) or cognitive function. A 2019 CADTH Rapid Response report reviewed a prospective cohort study conducted in Canada, in which the study authors concluded that exposure to higher levels of fluoride during pregnancy is associated with lower full-scale IQ scores in children aged 3 to 4 years. However, the CADTH review found the study findings did not support its conclusion, as the mean of Full scale IQ was not different between children from fluoridated and non-fluoridated areas, and the effect was only significant when the analysis was restricted to boys. There appear three recently published studies in the literature examining the association between fluoride exposure and IQ and attention deficit hyperactivity disorder (ADHD) in children. One study was conducted in China, and two studies were from Canada.^, The appearance of those studies prompted CADTH to conduct an updated review on the same topic.

The aim of this report is to update the previous CADTH reports^, by reviewing recent evidence on the effects of fluoride exposure through CWF at levels that are relevant to the Canadian context on the neurological or cognitive development in children and adolescents less than 18 years of age.

In this report, gender-neutral language has been used where possible in order to be inclusive of all gender identities. When reporting results from the published manuscript, gender-neutral language was not used in order to be consistent with the terms used in the source material.