Fluoride Action Network

Fluoride’s Mutagenicity: In vivo Studies

Fluoride Action Network | by Michael Connett | Updated April 2015

Consistent with dozens of in vitro studies, a number of in vivo studies, in both humans and animals, have found evidence of fluoride-induced genetic damage. In particular, research on humans exposed to high levels of fluoride have found increased levels of “sister chromatid exchange” (SCE). As noted in one study:

“In recent years, SCE analysis has been considered to be a sensitive method for detecting DNA damage. There is a clear relationship between a substance’s ability to induce DNA damage, mutate chromosomes, and cause cancers. The SCE frequency in the human body in peripheral blood lymphocytes is very steady, and does not vary with age or sex. Any increase of the SCE frequency is primarily due to chromosome damage. Thus using a method to detect SCE for exploring the toxicity and harm caused by fluoride is of great importance. The results in this paper showed an obvious increase in the SCE frequency of the patients with fluorosis, indicating that fluorine had some mutagenic effects, and could give rise to DNA damage.”
SOURCE: Wu DQ, Wu Y. (1995). Micronucleus and sister chromatid exchange frequency in endemic fluorosis. Fluoride. 28(3):125-127.

As with the in vitro researcher however, not every in vivo study has detected an increased rate of genetic damage in fluoride-exposed individuals. Some human and animal research has failed to detect an increase in genetic damage from high fluoride exposure. Specifically, the Oral Health Research Institute at the Indiana University School of Dentistry has repeatedly failed to find any evidence of genotoxic effects from fluoride exposure, whether in fluoride-exposed humans or animals. (Jackson 1997; Li 1995; Dunipace 1995; Jackson 1994). In light of the Indiana dental team’s findings, the evidence on fluoride’s in vivo mutagenicity remains unresolved.

In Vivo Human Studies

“Our results indicate that there is a significant increase in the frequencies of chromosome aberrations and SCE in one of the village populations exposed to a fluoride concentration higher than the permissible limit. The lymphocytes of these residents were also more susceptible to a clastogen such as Mitomycin-C than the other populations and displayed a significant increase in chromosome aberrations.”
SOURCE: Joseph S, Gadhia PK. (2000). Sister chromatid exchange frequency and chromosome aberrations in residents of fluoride endemic regions of South Gujarat. Fluoride 33(4):154-158.

“Our study here provides evidence that the air pollutants at the phosphate fertilizer factory, in which HF and SiF4 are the main chemicals, could induce both CA (chromosomal aberrations) and MN (micronuclei) in human blood lymphocytes in vivo. Our earlier observation on sister-chromatid exchanges (SCE) of peripheral blood lymphocytes from this same population showed that the mean SCEs/cell of the workers was significantly higher than that of the controls (p < 0.01). The results of our studies imply that even if the concentration of the chemical pollutants in the air is low (e.g. F 0.50-0.80 mg/m 3), it may cause damage to genetic material at the chromosomal level… it is suggested that chromosomal abnormalities induced by fluoride could be the results from interaction with the enzymes responsible for DNA synthesis or repair, rather than directly with DNA.”
SOURCE: Meng Z, Zhang B. (1997). Chromosomal aberrations and micronuclei in lymphocytes of workers at a phosphate fertilizer factory. Mutation Research 393: 283-288.

“The results in this paper showed an obvious increase in the SCE frequency of the patients with fluorosis, indicating that fluorine had some mutagenic effects, and could give rise to DNA damage. The fact that the SCE frequency of the healthy people in the endemic regions was also higher than that of the controls in the non-endemic regions suggests that early harm by fluorine can be cytogenetically detected in the sub-clinical patients with fluorosis who could not be given an early diagnosis clinically. Under normal circumstances, the incidence rate of micronucleus is very low, usually 0-2%. The normal value checked in this paper is 0-2%, which agrees with that reported in the literature. The results show that the mean value of the micronucleus rate of the fluorine-toxic patients was 1.94 + 0.86% (range 1-15%) which is 2-3 times more than that of 0.57 + 0.44% in the controls… To sum up, the rise of SCE and MN in the peripheral blood lymphocytes of the fluorine-intoxicated patients indicates that fluorine is a mutagenic agent which can cause DNA and chromosomal damage.”
SOURCE: Wu DQ, Wu Y. (1995). Micronucleus and Sister Chromatid Exchange Frequency in Endemic Fluorosis. Fluoride 28(3):125-127.

“Our study here provided evidence that the air pollutants at the phosphate fertilizer factory, of which HF and SiF4 are the main chemicals, could induce SCEs in human blood lymphocytes in vivo. These results imply that even if the concentration of the chemical pollutants in the air is low (e.g.F: 0.50 – 0.80 mg/m3), it may cause damage to genetic material at the chromosomal level, although the general health of the workers in the phosphate fertilizer factory was found to be satisfactory… HF and SiF4 are the main air pollutants; however, dust containing fluoride, phosphate fog, ammonia (NH3), and sulfur dioxide (SO2) were also released in small amounts into the air during fertilizer production. These pollutants may also make a contribution to the induction of SCES. Hence, further study of the induction effect of HF or SiF4 alone on SCEs in human lymphocytes to understand the cytogenetic damage of fluoride pollution in the air would be needed.”
SOURCE: Meng Z, et al. (1995). Sister-chromatid exchanges in lymphocytes of workers at a phosphate fertilizer factory. Mutation Research 334(2):243-6.

“A number of investigators have utilized the SCE (Sister Chromatid Exchange) test to study the genotoxicity of fluoride. In the present study, human populations directly exposed to fluoride in drinking water in endemic regions of North Gujarat were investigated to evaluate the possible effect of fluoride on SCE. To the best of our knowledge this is the first report on genotoxic effects following long-term fluoride intake in an endemic area in India… The results of the present investigation suggest that in fluoride-affected persons exposed to 1.95 – 2.2 ppm fluoride in drinking water chromosomal alterations as indicated by SCE frequency and chromosome aberrations were higher than in normal persons exposed to 0.6 – 1.0 ppm drinking water fluoride.”
SOURCE: Sheth FJ, et al. (1994). Sister chromatid exchanges: A study in fluorotic individuals of North Gujurat. Fluoride 27: 215-219.

“The article researches on the damage for fluorine pollution to children’s lung function and chrosmosome in a aluminum plant. . . . The results . . . indicate that the rate of micronuleus and abnormal of blood periphery lymphocyte is higher than that of children in contrast group. . . . It suggests that fluorine pollution has a certain damage to the children’s lung function and chromosome.”
SOURCE: Zhai H, et al. (1994). Research on fluorine pollution’s damage to children’s lung function and chromosome. Journal of Environment & Health. [Article in Chinese]

“With peripheral blood lymphocyte culture, a study of SCE and micronuclei testwas done in 24 patients with fluorosis and same number of normal people as control. The results obtained showed that in the patient group the mean value of SCE per cell and the frequency of micronuclei were 10.24±1.67 and 1.42‰ ,respectively, while in the control only 7.62 ± 0.80 and 0.33‰, respectively, were found. And both of the two respective parameters, statistically, were in significant difference. These findings suggested that excess fluorine would cause increases of SCE frequency and micronuclear number in lymphocyte and make DNA damaged.”
SOURCE: Li J, et al. (1991). The influence of high-fluorine on DNA stability in the human body. Chinese Journal of Endemiology.  [Article in Chinese]

Consensus View of In Vivo Animal Studies:

“The disagreements among the in vivo tests for chromosome damage in rodents can not yet be reconciled. There are a few reports of positive results for chromosome aberrations in rodent bone marrow and testes, but other studies, using similar protocols and dose ranges, have reported no induced chromosome damage… Therefore, at this time, the in vivo clastogenicity of fluoride should be considered unresolved.”
SOURCE: Department of Health and Human Services. (1991). Review of fluoride: benefits and risks. Report of the Ad Hoc Subcommittee on Fluoride. Washington, DC. p. 70.

Excerpts from In Vivo Animal Studies:

“The results concerning the SCE rate induced by sodium fluoride are shown in Table 1. Although no significant increase was observed with the two low doses tested (from 2 to 4 mg/kg), a significant SCE increase was found with the three highest doses. The cumulative frequency of these data reveals about 70% of cells with four SCE in the group treated with the high dose, a value which is twice the level of the negative control.”
SOURCE: Velazquez-Guadarrama N, Madrigal-Bujaidar E, Molina D, Chamorro G. (2005). Genotoxic evaluation of sodium fluoride and sodium perborate in mouse bone marrow cells. Bulletin of Environmental Contamination and Toxicology 74(3):566-72.

“We tested the induction of mutagenic effects by in vivo and in vitro bone marrow micronucleus tests. A significant increase in micronucleated polychromatic erythrocytes was observed 24 H after intraperitoneal injection of sodium fluoride at a dose of 30 mg/kg body weight. In the in vitro micronucleus test, the frequency of micronucleated polychromatic erythrocytes was increased significantly at concentrations of 2 and 4 MM. These results indicate that the micronucleus test may be useful in evaluating the cancer risk of sodium fluoride.”
SOURCE: Suzuki Y, Li J, Shimizu H. (1991). Induction of micronuclei by sodium fluoride. Mutation Research 253(3):278.

“Genotoxicity of Sodium fluoride was evaluated in mice in vivo with the help of different cytogenetic assays. The frequency of chromosome aberration was dose – and time – dependent but not exactly route-dependent. Fractionated dosing induced less aberration. Incidence of micronucleus and sperm abnormality increased with dose. Relative sensitivity of the three assays has been found to be: Sperm abnormality > Chromosome aberration > Micronucleus. The present results have revealed the mutagenic property of NaF.”
SOURCE: Pati PC, Bhunya SP. (1987). Genotoxic effect of an environmental pollutant, sodium fluoride, in mammalian in vivo test system. Caryologia 40:79-87.

“The test animals were fed with low-grade food during 2-5 months under conditions of acute and chronic action of hydrogen phosphide and hydrogen fluoride induced by inhalation, that resulted in the pronounced impairment of the chromosomal apparatus of the bone marrow cells in the rats. A principal possibility has been established of modification of the hydrogen phosphide and hydrogen fluoride cytogenetic effect by the alimentary action. In particular, it has been found that the effect is significantly higher when the rats are fed with a low-grade ration than under conditions of balanced nutrition.”
SOURCE: Tazhibaev ShS, et al. (1987). [Modifying effect of nutrition on the mutagenic activity of phosphorus and fluorine compounds]. Vopr Pitan. Jul-Aug;(4):63-6.

“Cytological studies on bone marrow cell chromosomes and spermatocytes showed that 1-200 ppm F (as sodium fluoride) was able to induce chromosomal changes in a dose-dependent manner. The frequency of the induced chromosomal damage was significantly higher in each treatment than in the controls. The observed abnormalities included translocations, dicentrics, ring chromosomes, and bridges plus fragments, or fragments by themselves. There was a significant correlation between the amount of fluoride in the body ash and the frequency of the chromosomal abnormalities.”
SOURCE: Mohamed AH, Chandler ME. (1982). Cytological effects of sodium fluoride on mice. Fluoride 15(3):110-18.

“Cryolite concentrations of 3 mg/m3 as well as a mixture of 0.5 mg/m3 of cryolite and 0.35 mg/m3 of hydrogen fluoride increases 3 1/2 to 4 1/2 times (over controls) the percentage of cells with chromosomal aberrations in the bone marrow of rats. The data indicate the need for further study of the mutagenic features of fluoride compounds in relation to their potential for harmful impact on the mechanism of inheritance in humans.”
SOURCE: Gileva EA, et al. (1975). The mutagenic activity of inorganic fluorine compounds. Fluoride 8(1):47-50. [Originally published in Russian; condensed from Gig. Sanit., 37(1):9-12, Jan. 1972.]

“The mutagenic effect of hydrogen fluoride in concentration 1.0 mg/m-3 was studied in rats and mice. Prolonged inhalation of this compound increased the frequency of cells with chromosome abnormalities in the bone marrow of albino rats. The mutagenic effect was higher in older animals.”
SOURCE: Voroshilin SI, et al. (1975). Mutagenic effect of hydrogen fluoride on animals. Tsitol Genet. 9(1): 42-44.

“On the grounds of the results obtained during our experiments F compounds are able to produce certain changes in chromosomes from somatic cells of animals treated in vivo by them… Most of the aberrations observed in the case of bone marrow cells were chromatid-type aberrations… [W]e entertain the opinion that the main damage to chromosomes during our experiments with F compounds also took part during the S-phase… [T]hese data enable us to consider as sufficiently established the conclusion that inorganic fluorine compounds may present a mutagenic danger to human beings.”
SOURCE: Voroshilin SI, et al. (1973). Cytogenetic effect of inorganic fluorine compounds on human and animal cells in vivo and in vitro. Genetika 9(4): 115-120.

“In 54 tests involving 991 mice bearing transplanted tumors and 58 tests including 1817 tumor-bearing eggs, data were obtained which indicated a statistically significant acceleration of tumor tissue growth in association with comparatively low levels of NaF.”
SOURCE: Taylor A, Taylor NC. (1965). Effect of sodium fluoride on tumor growth. Proceedings of the Society for Experimental Biology and Medicine 119:252-255.