According to the National Toxicology Program (NTP), “the preponderance of evidence” from laboratory studies indicates that fluoride is a mutagen (a compound that can cause genetic damage). A chemical that can cause genetic damage is one that can likely cause, or contribute to, the development of cancer.
While the concentrations of fluoride causing genetic damage in laboratory studies are generally far higher than the concentrations found in human blood, there are certain “microenvironments” in the body (e.g., the bones, bladder, kidneys, oral cavity, pineal gland) where cells can be exposed to fluoride levels that are comparable to those causing genetic damage in the laboratory. Moreover, some research has found that cells of primates (including great apes and humans) are more susceptible to fluoride’s mutagenic effects than cells of rodents. These factors may help explain why seven studies since the 1990s have found evidence of genetic damage in humans with high fluoride exposures. (Some studies have not found this association.)
The concern that fluoride can cause cancer has been fueled by evidence linking it to a serious form of bone cancer known as osteosarcoma. This evidence includes a government animal study as well as several studies of human populations living in the United States.
Osteosarcoma is a rare, but deadly, form of cancer that strikes primarily during the teenage years. A national case control study published in 2006 by Harvard scientists found that boys exposed to fluoridated water during their 6th, 7th, and 8th years of life (the mid-childhood growth spurt) had a significantly elevated risk of developing osteosarcoma during adolescence. (Bassin 2006). The sex-specific link between fluoride and osteosarcoma in young males is consistent with the government’s animal study, (NTP 1990), which found osteosarcomas in the fluoride-treated male rats, but not the female ones. It is also consistent with previous studies by the National Cancer Institute and New Jersey Department of Health, which both found associations between fluoridation and osteosarcoma in young males, but not females. (Cohn 1992; NCI 1990)
Although a number of studies have found no association between fluoride and osteosarcoma, the Harvard study by Bassin is the only study to ever carefully considered the “age-specific” risk of fluoride exposure. As the renowned epidemiologist Kenneth Rothman explained to the Wall Street Journal:
“‘If there were an adverse effect of fluoride, it’s possible an effect of early exposure would be manifest in the first 20 years of life – but not after.’ Looking at all ages, in other words, could conceal any link between fluoridation and cancer.”
It is widely acknowledged that the fluoride/osteosarcoma connection is a biologically plausible one. When the connection between a chemical and a cancer is biologically plausible, studies that detect an association between the two are taken more seriously, as the association is less likely to be a random fluke.
The plausibility of a fluoride/osteosarcoma connection is grounded in the three considerations:
In addition to osteosarcoma, a number of studies of fluoride-exposed workers have found associations between airborne fluoride exposure and both bladder and lung cancer. Although fluoride’s association with these cancers has generally been attributed to poly aromatic hydrocarbons (PAH) — a non-fluoride airborne contaminant – a twenty-year study of a workplace with no PAH exposure found a similarly elevated rate of both bladder and lung cancer in the fluoride-exposed workers. (Grandjean 2004). Based on these findings, the authors concluded that “fluoride should be considered a possible cause of bladder cancer and a contributory cause of primary lung cancer.”