Calcium Absorption in Postmenopausal Osteoporosis: Benefit of HRT Plus Calcitriol, but not HRT Alone, in both Malabsorbers and Normal Absorbers

Abstract

In a randomized trial involving 71 postmenopausal osteoporotic women with vertebral compression fractures, radiocalcium absorption studies using the (45)Ca single isotope method (alpha) were performed at baseline and after 8 months of treatment with either continuous combined hormone replacement therapy (HRT, as piperazine estrone sulfate 0.625-0.937 mg daily +/- medroxyprogesterone acetate 2.5 mg daily depending on uterine status) or HRT plus calcitriol 0. 25 microg twice daily. A calcium supplement of 600 mg nocte was given to only those women who had a daily calcium intake of less than 1 g per day at baseline, as assessed by recalled dietary intake. There was a significant decrease [0.74 (+/- 0.35 SD) to 0.58 (+/- 0. 22), Dalpha = -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 (+/- 0.27), Dalpha = +0.16 (+/- 0. 30), p<0.003] in the HRT-plus-calcitriol treated patients, resulting in alpha being significantly higher after 8 months in the latter group than in the HRT-only group. Although 72% of the patients had been supplemented with calcium between the first and second studies, separate analyses revealed that the change in calcium intake had not affected the result. Further breakdown of the groups into baseline 'normal' absorbers (alpha >/=0.55) and 'malabsorbers' (alpha <0.55) revealed that alpha decreased with HRT treatment only in the normal absorbers, and remained stable in the malabsorbers. Conversely, following HRT plus calcitriol treatment, alpha increased only in the malabsorbers, the normal absorbers in this group remaining unchanged. In conclusion, our data show that HRT, of the type and dose used in this study, did not produce an increase in absorption efficiency; it was in fact associated with a fall. Increased absorption efficiency cannot be achieved unless calcitriol is used concurrently, and then only in patients with malabsorption. Calcitriol also had a significant effect in normal absorbers in that it prevented the decline in alpha seen with HRT alone, and thus should be considered in all patients with postmenopausal osteoporosis treated with HRT.

Ingestion of Raffinose Promotes Calcium Absorption in the Large Intestine of Rats

“…5) Holzherr et al 6) and Kalu 7) reported similar observations in human and animals, and our previous report also agreed with these results that ovarian hormone deficiency impaired ability of calcium absorption in rats everted intestinal sacs. 8) The presence of estrogen receptors in rat duodenal cells were confirmed and estrogen stimulates intestinal calcium absorption via an estrogen receptor.…”

Comparison of the effects of cholecalciferol and calcitriol on calcium metabolism and bone turnover in Chinese postmenopausal women with vitamin D insufficiency

“…In elderly people, diminished renal function due to aging leads to a decrease in renal conversion to 1,25(OH) 2 D 3 [12] . Calcitriol [1,25(OH) 2 D 3 ] plays an important role in promoting bone formation, and D-hormone analogs prevent falls to a greater extent than does ordinary vitamin D. Therefore, the use of D-hormone analogs has been advocated for the treatment of osteoporosis in many studies [13][14][15] . Because patients who are treated with 0.5 μg/d or 1.0 μg/d of calcitriol tend to develop hypercalcinuria, serum and urinary calcium levels should be examined regularly, and the calcitriol regime should be examined intermittently.…”

Effect of Treatment with Oral Calcitriol on Calcium Metabolism and Fasting Serum 25(OH)- or 1,25(OH)2-Vitamin D Level in Japanese Postmenopausal Women

“…In several other countries, studies demonstrated the clinical effectiveness of long-term calcitriol supplement in postmenopausal osteoporosis [3][4][5][6]. While an impaired intestinal calcium absorption is partly responsible for postmenopausal osteoporosis [3,4], Riggs and Nelson successfully demonstrated that calcium absorption could be normalized by small doses of calcitriol in postmenopausal osteoporosis [5].…”