The effect of water fluoridation on the bone mineral density of young women

Abstract

The effect of long term exposure to low level water fluoridation on BMD (bone mineral density) was studied in a sample of female university students (18 to 25 years). Subjects were 24 women from Regina, Saskatchewan (natural level of fluoride in the drinking water is 0.1 mg./litre) and 33 women from Saskatoon, Saskatchewan (supplementation of fluoride in the drinking water is 1.0 mg./litre). These two cities are very similar in population, climate and demographic data. The subjects had not moved outside of their resident city for more than four years, had no bone affecting medical disorders and were not using any bone affecting medications. All subjects completed a lifestyle and dietary history evaluation and a food frequency questionnaire. There were no differences between the two groups for age, weight, height, bone mineral free lean mass, fat mass, estrogen status, calcium and vitamin D intake, and past or present physical activity level. Areal bone mineral density of the proximal femur, lumbar spine (AP and lateral companion scan) and total body were measured using dual energy x-ray absorptiometry (Hologic 2000, array mode). Volumetric BMD was also determined for the lumbar spine from the AP and lateral companion spine scans (VLS). The hypotheses predicted greater BMD in the fluoridated community as compared to the non-fluoridated community, with the greatest difference occuring at the axial skeleton. To determine an overall difference in BMD between Regina and Saskatoon groups, MANCOVA was performed with place of residence as the independent variable and AP Spine, Total Body and Total Proximal Femur BMD as the dependent variables. Weight was used as the covariate. There was a significant difference between Regina and Saskatoon adjusted mean BMD (F (52,3) = 2.44, p < 0.05, one-tailed). Posthoc univariate F-tests found the differences in BMD were due to differences at the AP Spine (Regina = 0.975 g/cm2 , Saskatoon = 1.039 g./cm2 , F (54, 1) = 7.33, p < 0.05, one-tailed), and Total Body (Regina= 1.044 g/cm2 , Saskatoon = 1.073 g/cm2 , F (54,1) = 3.16, p < 0.05, one-tailed), but not at the proximal femur. Based on the significant finding at the axial spine, ANCOVA was performed for the lateral companion spine (L3) and VLS (L3). There was a significant difference between the Regina and Saskatoon groups at VLS ((L3), Regina= 0.216 g/cm3 , Saskatoon= 0.227 g/cm3 , F (53,1) = 4.37, p < 0.05, one-tailed). This study supports that low level water fluoridation may have a positive effect on the bone mineral density of young women, the greatest effect occurring at the axial skeleton.