Are fluoride levels in drinking water associated with hypothyroidism prevalence in England? A large observational study of GP practice data and fluoride levels in drinking water
Journal or Publication
Journal of Epidemiology & Community Health
S Peckham, D Lowery, S Spencer
Tanvi Dusane, BDS, MPH
Level of rigor
- A - Strong methodology and unbiased, appeared in peer-reviewed in respected science journal
- B - Strong methodology and unbiased, not in peer-reviewed journal
- C - Weak methodology and/or biased
- F - Not a scientific finding
Support from other studies
- High - All the peer-reviewed research to date support these findings, and a significant amount of research has been done in this area.
- Medium - Most, but not all, peer-reviewed research to date support these findings, and a significant amount of research has been done in this area.
- Low - Not a lot of research has been done in this area, or some, but not most, other peer-reviewed research supports these findings.
- Not Supported - No other studies support this study's conclusions.
- Contradicted - Most studies contradict this study's conclusions.
This is the first large population-level assessment of the association between fluoride level in water and practice-level prevalence of hypothyroidism. The study has good measures for prevalence of hypothyroidism in medical practices.
This study has important limitations in its design: This is an ecological study and the findings are at risk for the ecological fallacy. That is, findings may not be true at the level of the individual. Individuals with hypothyroidism may not have been exposed to the levels of fluoride in drinking water that were used in the study. Other potential confounding factors have not been taken into account (i.e...iodine intake, medical history, family history, smoking) The authors’ inaccurate interpretation of the findings from previous studies on fluoride in drinking water and thyroid function may have generated bias.
Relevance and validity
This is an ecological assessment using secondary data of private care practice-level prevalence of hypothyroidism in England and fluoride level in drinking water. The validity of the study’s findings may suffer from ecological bias. Other limitations in study design involve lack of control for other potential confounders and lack of assessment of iodine intake.