High Fluoride in Drinking Water May Be Linked To Hypothyroidism

MedicalResearch.com Interview with:
Professor Stephen Peckham
Director, Centre for Health Services Studies
Professor of Health Policy
Department of Health Services Research and Policy
London School of Hygiene and Tropical Medicine
Director, Policy Research Unit in Commissioning and the Healthcare System University of Kent

Medical Research: What is the background for this study? What are the main findings?

Response: Community water fluoridation remains a controversial public health measure. There have been continued debates about both its effectiveness in the prevention of dental caries and also its safety. Previous studies have suggested that there is an association between fluoride ingestion and the incidence of hypothyroidism few population level studies have been undertaken. In April 2014 Public Health England published a monitoring report that used secondary analysis of routine health statistics to identify whether water fluoridation in England was associated with any adverse health outcomes. While hypothyroidism data is available this was not included in their monitoring report.  In England approximately 10% of the population lives in areas with community fluoridation schemes and hypothyroidism prevalence can be assessed from general practice data. Tt examine whether there is a relationship – as suggested in smaller studies – we used a cross-sectional study design using secondary data to develop binary logistic regression models of predictive factors for hypothyroidism prevalence at practice level using 2012 data on fluoride levels in drinking water, 2012/13 Quality Outcomes Framework (QOF) diagnosed hypothyroidism prevalence data, 2013 General Practitioner (GP) registered patient numbers, and 2012 practice level Index of Multiple Deprivation scores. We found a positive association between fluoride levels and hypothyroidism. High hypothyroidism prevalence was found to be at least 30% more likely in practices located in areas with fluoride levels in excess of 0.3mg/L. This population study supports earlier hypotheses that fluoride is associated with hypothyroidism. In the UK water is fluoridated at 1ppm (1mg/L) and in areas where water is fluoridated the model predicts that after controlling for other factors, practice populations are significantly more likely to have higher levels ofhypothyroidism than those in non-fluoridated areas. Higher levels of fluoride in drinking water, therefore, provide a useful contribution for predicting prevalence of hypothyroidism. For example in contrasting two urban areas we found that practices located in the West Midlands (a wholly fluoridated area) are nearly twice as likely to report high hypothyroidism prevalence in comparison to Greater Manchester (non-fluoridated area).

Medical Research: What should clinicians and patients take away from your report?

Response: The finding of this cross-sectional study has important implications for public health policy in the UK and in other countries where fluoride is added to drinking water or in other forms such as fluoridated milk and salt. In many areas of the world hypothyroidism is a major health concern and in addition to other factors – such as iodine deficiency – fluoride exposure should be considered as a contributing factor. To minimize the risk of increasing the prevalence of hypothyroidism, it is important, therefore, to limit fluoride ingestion from all sources. This would be particularly important in areas where iodine concentrations are low, given the potential action of fluoride as an iodine inhibitor. Consideration needs to be given to reducing fluoride exposure and public dental health interventions should stop interventions reliant on ingested fluoride and switch to topical fluoride and non-fluoride based interventions. The findings of the study raise particular concerns about the validity of community fluoridation as a safe public health measure.

Medical Research: What recommendations do you have for future research as a result of this study?

Response: There are some limitations to this observational study but the use of large scale data and using practice populations has enabled greater confidence in the reported findings. However, future research which measures individual fluoride exposure would be useful.