THE INCREASE IN SPINAL BONE-DENSITY THAT OCCURS IN RESPONSE TO FLUORIDE THERAPY FOR OSTEOPOROSIS IS NOT MAINTAINED AFTER THE THERAPY IS DISCONTINUED

In 44 osteoporotic subjects who had been treated with fluoride for 37 +/- 16 months, the fluoride was discontinued because they had shown fl uoride-dependent increases in trabecular spinal bone densities from lo w initial levels (below the fracture threshold) to values that were eq uivalent to normal peak bone densities in the spines of young adults. During the subsequent period, after discontinuation of the fluoride th erapy (i.e. 19 +/- 9 months), spinal bone density decreased in 73% of the subjects (i.e. 32 of 44, p<0.03), at a rate that was comparable to the rate of the previous gain that had occurred during the treatment with fluoride (i.e. -3.23 +/- 2.39 mg/cm(3) per month, compared with 3.91 +/- 1.96 mg/cm(3) per month in this subgroup of patients, p<0.001 ). Although 9 of the 44 subjects showed continuing increases in spinal bone density after discontinuation of the fluoride therapy, spinal bo ne density decreased in the entire group of 44 at an average rate of - 1.02 +/- 4.72 mg/cm(3) per month (p<0.001, compared with the rate of t he previous gain during the treatment with fluoride; i.e. +3.83 +/- 1. 82 mg/cm(3) per month). Surprisingly, our data showed that the rate of decrease in spinal bone density during the post-fluoride period was n ot affected by concurrent (undesigned) treatment with calcium, calcium plus estrogen, or calcium plus calcitriol. The cessation of fluoride therapy was also associated with a decrease in serum alkaline phosphat ase activity (i.e. a decrease from the elevated levels that were obser ved during the period of fluoride therapy, back to the original, pre-t reatment levels; p<0.001), and that the rate of spinal bone loss after cessation of fluoride could be correlated with the prior rate of incr ease in serum alkaline phosphatase activity that had occurred during t he treatment with fluoride (n = 44, r = 0.312,p = 0.039). Together, th e observations from this retrospective analysis of data obtained from our clinical subjects suggest that fluoride-treated osteoporotic subje cts who have exhibited increases in trabecular spinal bone density are at risk for bone loss after discontinuation of the fluoride therapy.