Most health experts who’ve reviewed the research on these issues say the recommended levels of fluoride added to U.S. drinking water aren’t high enough to pose serious risks, says Zavras. “If the fluoride in the water is well controlled and remains at optimal levels, there should not be a reason to worry,” Zavras says.
Here’s a recap of some of the research.
Arthritis
One study of 1,128 Chinese adults found that people exposed to higher doses of fluoride in drinking water were roughly twice as likely to develop knee osteoarthritis as individuals with the lowest exposure levels.
It’s important to note that China recommends higher levels of fluoride in drinking water than in the United States does, and also has naturally high levels of fluoride in groundwater, averaging 0.9 mg per liter and reaching as high as 60 mg, according to another study.
“These concentrations are far above the carefully regulated fluoride level of 0.7 mg/L used in U.S. drinking water,” says Marcelle Nascimento, DDS, PhD, a professor and an assistant dean of clinical research at the University at Buffalo School of Dental Medicine. “Decades of evidence support the safety of fluoridation at [U.S.] levels.”
Bone Fractures
One study of 1,413 children and adolescents in the United States found higher levels of fluoride in drinking water associated with lower bone mineral density; denser bones are stronger and more resistant to fractures.
But the results were inconclusive; researchers didn’t find any connection between bone density and fluoride levels in urine, which measures all the fluoride people are exposed to through drinking water and other sources.
A recent meta-analysis of 28 studies found that fluoride was associated with a risk of fractures, but only at levels more than double what’s recommended for U.S. drinking water.
Similarly, a report from WHO examining research to date on the fracture risk associated with fluoride in drinking water found a risk of all fractures with fluoride levels above 4.3 mg per liter and a risk of hip fractures at exposure levels above 6.5 mg per liter. The WHO noted in their report that these results were not statistically significant, meaning they might be due to chance. The WHO research report also notes that in some countries, including China and India, fluoride exposure from drinking water isn’t typically as high as exposure from food.
“There is no credible evidence connecting regulated fluoride in U.S. drinking water to arthritis or fractures,” Dr. Nascimento says.
Bone Cancer
A study of 2,566 patients with bone cancer and 1,650 patients with Ewing sarcoma, tumors of the bones and soft tissue, found no connection between these malignancies and fluoride levels in drinking water.
The WHO research review concluded that there is insufficient evidence to suggest that fluoride in drinking water causes bone cancer while conceding that there is relatively little data on this connection.
Thyroid Disease
A meta-analysis of 33 studies found abnormal levels of thyroid hormones, a marker of thyroid disease, but only when people were exposed to drinking water with more than 2.0 mg of fluoride per liter of water — more than double the recommended amount for municipal water in the United States.
Research linking fluoride to thyroid disorders have found potential risk at levels of 3 mg to 10 mg per liter — much higher than than the U.S. standard for drinking water, Nascimento says.
“At very high doses, fluoride can affect iodine metabolism, which is related to thyroid function,” Nascimento says. “However, research consistently shows that fluoride at the levels used in U.S. public water systems does not pose a risk to thyroid health. There is no credible evidence to suggest that fluoridated water at regulated levels in the United States is associated with thyroid disorders.”
