The majority of animal studies investigating fluoride’s impact on bone strength have found that fluoride has either no effect, or a detrimental effect, on bone strength.
Importantly, several of the animal studies that have found fluoride reductes bone strength have reported that this reduction in strength occurs before signs of skeletal fluorosis are detectable. Similar findings have been reported in human clinical trials. It appears evident, therefore, that fluoride can reduce bone strength before the onset of skeletal fluorosis. As such, the safe level of fluoride for bones can not simply be premised (as it has been for years) on only protecting against skeletal fluorosis.
Bone Fluoride Content vs. Density/Strength in a Fluoridated Community (Toronto)
“the density is unaltered, but the strength of the bone is lower for the more fluoridated group, which is consistent with some previous animal studies.”
SOURCE: Chachra D, et al. (2010). The long-term effects of water fluoridation on the human skeleton. Journal of Dental Research 89:1219-1223.
Human Clinical Trials
“In the seven patients with early (less than 1.1 year) spontaneous hip fractures, none had fluorosis at the time of their first fracture.”
SOURCE: Gutteridge DH, et al. (1990). Spontaneous hip fractures in fluoride-treated patients: potential causative factors. Journal of Bone and Mineral Research 5(Suppl 1):S205-15.
“there was no obvious difference in the histological appearance of bone of those who developed fractures compared with those who did not.”
SOURCE: Hedlund LR, Gallagher JC. (1989). Increased incidence of hip fracture in osteoporotic women treated with sodium fluoride. Journal of Bone and Mineral Research 4:223-5.
“The results suggest that genetic factors may contribute to the variation in bone response to fluoride exposure and that fluoride might affect bone properties without altering BMD.”
SOURCE: Mousny M, et al. (2006). The genetic influence on bone susceptibility to fluoride. Bone Aug 18; [Epub ahead of print]
“Mineralization defects were not observed in microradiographs of femora and vertebrae from the current study, so it is unclear by what mechanism fluoride impaired bone strength.”
SOURCE: Turner CH, et al. (1997). Fluoride treatment increased serum IGF-1, bone turnover, and bone mass, but not bone strength, in rabbts. Calcified Tissue International 61: 77-83.
“The mineral distribution in the vertebrae of minipigs treated with NaF did not show any mineralization defects at the micrometer level. However, an investigation of the bone mineral at the nanometer level using SAXS showed small but significant differences between the NaF and the two other groups… It is, therefore, very likely that part of the reduction of bone strength following NaF treatment was due to a change in the material structure of bone at the nanometer level.”
SOURCE: Fratzl P, et al. (1996). Effects of sodium fluoride and alendronate on the bone mineral in minipigs: a small-angle x-ray scattering and backscattered electron imaging study. Journal of Bone and Mineral Research 11: 248-253.
“The reason for the fluoride-induced changes are not known. No osteomalacia or other histological changes, including focal osteomalacia or mottled periosteocytic lacunae, were seen on thorough histological examination. No woven bone was seen or changes in the lamellar structure. Fluoride content could decrease the mechanical properties of bone as a result of its effects on crystal structure or matrix properties or defects that we failed to detect.”
SOURCE: Lafage MH, et al. (1995). Comparison of alendronate and sodium fluoride effects on cancellous and cortical bone in minipigs: a one year study. Journal of Clinical Investigations 95: 2127-2133.
“[T]here were no signs of bone pathology, even though bone strength was reduced.”
SOURCE: Turner CH, et al. (1995). Fluoride reduces bone strength in older rats. Journal of Dental Research 74: 1475-1481.
“We have shown unequivocal reductions in bone strength in rats that were not associated with osteomalacia.”
SOURCE: Turner CH, Dunipace AJ. (1993). On fluoride and bone strength. Calcified Tissue International 56: 415-418.
“The bone strength deficit caused by fluoride accumulation in bone is not always associated with gross bone pathology (i.e. woven bone formation), but may be caused by decreased bone lipid content and calcification defects induced by decreased bonding strength at the crystal-matrix interface.”
SOURCE: Turner CH, et al. (1993). A mathematical model for fluoride uptake by the skeleton. Calcified Tissue International 52: 130-138.
“the conclusion by Einhorn et al that fluoride’s effects on bone are due to pathological bone remodeling are in conflict with findings showing a bone strength deficit caused by fluoride accumulation in the absence of gross pathology (i.e. woven bone formation).”
SOURCE: Turner CH, Dunipace AJ. (1993). On fluoride and bone strength. Calcified Tissue International 53: 289-290.