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 fluoride-dependent increases in trabecular spinal bone densities from low initial levels (below the fracture threshold) to values that were equivalent to normal peak bone densities in the spines of young adults. During the subsequent period, after discontinuation of the fluoride therapy (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/cm3 per month, compared with + 3.91 +/- 1.96 mg/cm3 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 bone density decreased in the entire group of 44 at an average rate of -1.02 +/- 4.72 mg/cm3 per month (p < 0.001, compared with the rate of the previous gain during the treatment with fluoride; i.e. +3.83 +/- 1.82 mg/cm3 per month). Surprisingly, our data showed that the rate of decrease in spinal bone density during the post-fluoride period was not 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 phosphatase activity (i.e. a decrease from the elevated levels that were observed during the period of fluoride therapy, back to the original, pre-treatment levels; p < 0.001), and that the rate of spinal bone loss after cessation of fluoride could be correlated with the prior rate of increase in serum alkaline phosphatase activity that had occurred during the treatment with fluoride (n = 44, r = 0.312, p = 0.039). Together, the observations from this retrospective analysis of data obtained from our clinical subjects suggest that fluoride-treated osteoporotic subjects who have exhibited increases in trabecular spinal bone density are at risk for bone loss after discontinuation of the fluoride therapy.