All four primary studies consistently found a negative relationship between chronic exposure to high levels of fluoride (more than 3.15mg per L) and IQ in children when compared to children who live in areas with lower levels of fluoride in the drinking water (less than 1.0mg per L). The meta-analysis also reported the same relationship in 12 of the 16 studies examined. One of the four primary studies found a statistically significant increase in proportion of children with IQ of less than 80 when mean fluoride level in the water was 2.46±0.25mg per L.

Application to US populations is hampered by several limitations:

• Fluoride levels are often confounded with levels of other known neurotoxins (such as arsenic) in the studies, as fluoride was naturally occurring
• All populations studied were non-US settings (one Mexican and the rest Chinese); therefore, exposure levels and confounding factors may be quite different than in a US setting
• While none of the studies found an association between IQ and fluoride levels below 1.0mg per L, this research cannot be used to identify a safe upper limit. 

• Grade I means there is Good/Strong evidence supporting the statement;
• Grade II is Fair;
• Grade III is Limited/Weak;
• Grade IV is Expert Opinion Only;
• Grade V is Not Assignable.
• High (A) means we are very confident that the true effect lies close to that of the estimate of the effect;
• Moderate (B) means we are moderately confident in the effect estimate;
• Low (C) means our confidence in the effect estimate is limited;
• Very Low (D) means we have very little confidence in the effect estimate.
• Ungraded means a grade is not assignable.

Water fluoridation with silicofluoride (but not sodium fluoride) may be associated with increased risk of elevated blood lead levels in children, especially those already at risk for lead exposure.

• Grade I means there is Good/Strong evidence supporting the statement;
• Grade II is Fair;
• Grade III is Limited/Weak;
• Grade IV is Expert Opinion Only;
• Grade V is Not Assignable.
• High (A) means we are very confident that the true effect lies close to that of the estimate of the effect;
• Moderate (B) means we are moderately confident in the effect estimate;
• Low (C) means our confidence in the effect estimate is limited;
• Very Low (D) means we have very little confidence in the effect estimate.
• Ungraded means a grade is not assignable.

There is no conclusive evidence of an association between fluoride intake and rate of Down Syndrome births.

• Grade I means there is Good/Strong evidence supporting the statement;
• Grade II is Fair;
• Grade III is Limited/Weak;
• Grade IV is Expert Opinion Only;
• Grade V is Not Assignable.
• High (A) means we are very confident that the true effect lies close to that of the estimate of the effect;
• Moderate (B) means we are moderately confident in the effect estimate;
• Low (C) means our confidence in the effect estimate is limited;
• Very Low (D) means we have very little confidence in the effect estimate.
• Ungraded means a grade is not assignable.