What the research found
Both thyroid outcome and fluoride exposure were measured at individual level as follows:
Fluoride exposure measures
- Fluoride level in spot urine sample
- Fluoride concentration in primary drinking water (mg/L) + self-report on residential history (at least 3 years of consecutive residence)
- Self-reported use of fluoride containing toothpaste and or mouthwash as well as history of fluoride treatment at dental office
Thyroid outcome measures
- Self-reported diagnosis of thyroid condition (yes/no)
- Serum thyroid stimulating hormone (TSH) level (low/normal/high)
No significant association was found between fluoride exposure measured in urine and tap water samples and self-reported diagnosis of a thyroid condition or altered (low or high) TSH levels. Fluoride exposure, in a time and place where multiple sources of fluoride including community water fluoridation exist, is not associated with impaired thyroid functioning in a representative sample of the Canadian population.
Canada has fluoridation program guidelines that are similar to the US, and the findings are relevant to the US and other countries with similar populations and CWF schemes.