Calcium absorption in postmenopausal osteoporosis: Benefit of HRT plus calcitriol, but not HRT alone, in both malabsorbers and normal absorbers

In a randomized trial involving 71 postmenopausal osteoporotic women with v ertebral compression fractures, radiocalcium absorption studies using the C a-45 single isotope method (alpha) were performed at baseline and after 8 m onths of treatment with either continuous combined hormone replacement ther apy (HRT, as piperazine estrone sulfate 0.625-0.937mg daily +/- medroxyprog esterone acetate 2.5 mg daily depending on uterine status) or HRT plus calc itriol 0.25 mu g twice daily. A calcium supplement of 600 mg nocte was give n to only those women who had a daily calcium intake of less than 1 g per d ay at baseline, as assessed by recalled dietary intake. There was a signifi cant decrease 0.74 (+/- 0.35 SD) to 0.58 (+/- 0.22), Delta alpha = -0.17 (/- 0.26), p<0.0005] in alpha at 8 months compared with baseline in the HRT- treated group, but a significant increase [0.68 (+/- 0.31) to 0.84 (+/- 0.2 7), Delta alpha = +0.16 (+/- 0.30), p<0.003] in the HRT-plus-calcitriol tre ated patients, resulting in alpha being significantly higher after 8 months in the latter group than in the HRT-only group. Although 72% of the patien ts had been supplemented with calcium between the first and second studies, separate analyses revealed that the change in calcium intake had not affec ted the result. Further breakdown of the groups into baseline 'normal' abso rbers (alpha greater than or equal to 0.55) and 'malabsorbers' (alpha <0.55 ) revealed that alpha decreased with HRT treatment only in the normal absor bers, and remained stable in the malabsorbers. Conversely, following HRT pl us calcitriol treatment, alpha increased only in the malabsorbers, the norm al absorbers in this group remaining unchanged. In conclusion, our data sho w that HRT, of the type and dose used in this study, did not produce an inc rease in absorption efficiency; it was in fact associated with a fall. incr eased absorption efficiency cannot be achieved unless calcitriol is used co ncurrently, and then only in patients with malabsorption. Calcitriol also h ad a significant effect in normal absorbers in that it prevented the declin e in alpha seen with HRT alone, and thus should be considered in all patien ts with postmenopausal osteoporosis treated with HRT.