CALCIUM DEFICIENCY IN FLUORIDE-TREATED OSTEOPOROTIC PATIENTS DESPITE CALCIUM SUPPLEMENTATION

To test the hypothesis that the osteogenic response to fluoride can in crease the skeletal requirement for calcium, resulting in a general st ate of calcium deficiency and secondary hyperparathyroidism, we assess ed calcium deficiency, spinal bone density by quantitative computed to mography, and serum PTH in three groups of osteoporotic subjects. Two of the three groups had been treated with fluoride and calcium (at lea st 1500 mg/day) for 32 +/- 19 months. Group I consisted of 16 fluoride -treated subjects who had shown rapid increases in spinal bone density (+3.8 +/- 2.6 mg/cm(3) month), group II consisted of 10 fluoride-trea ted subjects who had shown decreases or only slow increases in spinal bone density (-0.05 +/- 0.6 mg/cm(3) month), and group III consisted o f 10 age-matched untreated osteoporotic controls. Calcium deficiency w as assessed by measurement of calcium retention after calcium infusion . The results of our studies showed that 1) 94% of the subjects in Gro up I were calcium deficient compared with only 30% in groups II and II I (P < 0.01 for each); 2) the subjects in group I retained more calciu m (79%) than the subjects in group II (60%, P < 0.001) or the subjects in group III (64%, P < 0.005); 3) calcium retention was proportional to serum PTH (r = 0.37, n = 36, P < 0.03); and 4) calcium retention wa s proportional to the (previous) fluoride-dependent increase in quanti tative computed tomography spinal bone density (in groups I and II, r = 0.48, n = 26, P < 0.02). To test the hypothesis that the calcium def iciency and the secondary hyperparathyroidism that were associated wit h the positive response to fluoride would respond to concomitant calci triol treatment, a subgroup of 7 calcium-deficient subjects were selec ted from group I and treated with calcitriol (plus fluoride and calciu m) for an average of 7 months. The calcitriol therapy reduced the calc ium deficit in all 7 subjects, decreasing calcium retention from 80% t o 62% (P < 0.02), and decreasing PTH from 50 to 28 pg/mL (P < 0.02). T ogether, these data indicate that fluoride-treated osteoporotic subjec ts may develop calcium deficiency in proportion to the effect of fluor ide to increase bone formation, and this calcium deficit is responsive to calcitriol therapy.