Bone quality in fluoride-exposed populations: A novel application of the ultrasonic method

Various studies, mostly with animals, have provided evidence of adverse impacts of fluoride (F^-) on bone density, collagen and microstructure, yet its effects on overall bone quality (strength) has not been clearly or extensively characterized in human populations.

In this observational study, we assessed variation in an integrated measures of bone quality in a population exposed to wide-ranging F^- levels (0.3 to 15.5 mg/L) in drinking water, using a novel application of non-ionizing ultrasonic method.

We collected 871 speed of sound (SOS) measurements from 341 subjects residing in 25 communities, aged 10-70 years (188 males and 153 females). All subjects received scans of the cortical radius and tibia, and adults over the age of 19 received an additional scan of the phalanx. Associations between F^- in drinking water and 24-h urine samples, and SOS as a measure of bone quality, were evaluated in bivariate and multivariable regressions adjusting for age, sex, BMI, smoking, and toothpaste use.

We found negative associations between F^- exposure and bone quality at all three bones. Adult tibial SOS showed the strongest inverse association with F^- exposure, which accounted for 20% of the variance in SOS measures (r = 0.45; n = 199; p < 0.0001). In adjusted analysis, a 1 mg/L increase in F^- in drinking water was related to a reduction of 15.8 m/s (95% CI: -21.3 to -10.3), whereas a 1 mg/L increase in 24-h urinary F^- (range: 0.04-39.5 mg/L) was linked to a reduction of 8.4 m/s (95% CI: -12.7, -4.12) of adult tibial SOS. Among adolescents, in contrast, weaker and non-significant inverse associations between F^- exposure and SOS were found, while age, gender, and BMI were more significant predictors than in adults.

These results are indicative of a fluoride-induced deterioration of bone quality in humans, likely reflecting a combination of factors related to SOS: net bone loss, abnormal mineralization and collagen formation, or altered microarchitecture. The portable and low-cost ultrasound technique appears potentially useful for assessment of bone quality, and should be tested in other locations and for other bone-related disorders, to assess the feasibility of its more extensive diagnostic use in hard-to-reach rural regions.