Calcium Supplementation with and without Hormone Replacement Therapy To Prevent Postmenopausal Bone Loss

Postmenopausal bone loss is a major factor in the increasing prevalence of osteoporotic fractures. Evidence is abundant that hormonal replacement therapy prevents the bone loss that follows natural or surgical menopause and reduces the prevalence of osteoporotic fractures in later life [1-4]. However, only about 10% of American women elect to receive replacement therapy because of attitudes of physicians and patients, the undesirability of menstrual bleeding, and unresolved questions about the relation of the use of estrogen to breast cancer [5]. Moreover, the duration of hormonal therapy may need to be prolonged because bone loss recurs when therapy is discontinued, yet the incidence of some adverse effects increases with the duration of estrogen use. Safer alternatives to estrogen use have been sought. Epidemiologic and cross-sectional studies have suggested that increasing calcium intake might prevent postmenopausal bone loss, and prospective studies have yielded conflicting results [6-17]. Moreover, some investigators have suggested that effects differ on the various skeletal sites used to determine the rate of bone loss [18]. We compared the efficacy of calcium augmentation in early postmenopause with calcium augmentation plus hormonal replacement therapy and with placebo. The study had a three-arm, randomized, parallel design. The patients receiving hormonal replacement therapy were obviously not blinded nor were their physicians, whereas the placebo and calcium groups were double blinded. Methods Healthy, white women between 6 months and 6 years after a natural menopause were recruited to participate in the study. The protocol was approved by the Human Investigation Review Committees of Winthrop-University Hospital and Brookhaven National Laboratory; written informed consent was obtained from each participant. Participants were recruited by announcements in the local press and in hospital and university publications and through a direct mail campaign. All participants had a history and physical examination. Exclusion characteristics included any disorder known to affect bone metabolism such as glucocorticoid use, gastrointestinal disease, or any chronic illness. Previous or current malignancy was an exclusion characteristic as were absolute contraindications to estrogen replacement or calcium supplements. Absolute contraindications to estrogen replacement therapy included estrogen-dependent neoplasm (breast or uterus), undiagnosed vaginal bleeding, thrombophlebitis or thromboembolism, and acute liver disease. Women with the following problems considered by some investigators to be relative contraindications to estrogen therapy were also excluded: gallbladder disease, history of liver disease, first-degree relatives with breast cancer, and hypertension. Calcium urolithiasis was also an exclusion factor. Women with known osteoporosis or with a vertebral compression fracture were not eligible for the study. One hundred eighteen women entered the study. The women were randomly assigned to three groups: 1) hormonal replacement [estrogen-progesterone-calcium carbonate], 2) calcium carbonate, or 3) placebo. Assignment to the groups was based on computer-generated random numbers provided by the statistician, with stratification for years postmenopause. The women in the hormonal replacement group took conjugated equine estrogens (Premarin, Wyeth-Ayerst Laboratories, Inc.; Philadelphia, Pennsylvania), 0.625 mg daily for 25 days of the month along with medroxyprogesterone (Provera, Upjohn; Kalamazoo, Michigan), 10 mg from days 16 to 25. All women received 400 IU of vitamin D daily in the form of a multivitamin, and calcium supplementation (as Caltrate, Lederle; Clifton, New Jersey) was provided to the two treatment groups. The duration of the study was 2.9 1.1 years (mean SD). A 7-day dietary history was reviewed with a nutritionist every 2 months; calcium was provided as calcium carbonate, 600 mg (Caltrate), and used to supplement the diet to approximate a total daily intake of 1700 mg of elemental calcium (the mean + 2 SD found by Heaney and colleagues [7] to result in zero calcium balance in estrogen-deprived women). The calcium supplements were taken with meals in divided doses. The placebo appeared identical to the calcium carbonate tablets. No patients took antacids or histamine-2 blockers. All women had a baseline mammogram. Measurements Routine laboratory studies included a complete blood count, urinalysis, and serum fasting calcium, phosphorus, urea nitrogen, creatinine, alkaline phosphatase, cholesterol, and aminotransferase measurements [19, 20]. In addition, follicle-stimulating hormone, estradiol, parathyroid hormone, osteocalcin, free thyroxine, and bone alkaline phosphatase were measured, and a urine specimen was collected after an overnight fast for hydroxyproline, calcium, and creatinine determinations, following a 3-day low-hydroxyproline diet [21-23]. Total body calcium was measured annually in the participants, using the delayed neutron activation method at Brookhaven National Laboratory [24, 25]. This method uses a whole-body counter to measure the characteristic rays emitted from the neutron capture of Calcium-48 (natural abundance of 0.187%) in the body. The Brookhaven National Laboratory whole-body counter was upgraded in 1987 to use 32 NaI (T1) detectors of 10 cm 10 cm 46 cm positioned symmetrically above and below the patient [25]. The activated isotope, Calcium-49, decays with a half-life of 8.72 minutes, emitting a 3.08 MeV characteristic line. More than 99.5% of the body calcium is contained in the bone [26]. The method provides total body calcium with a coefficient of variation of about 1.5% when no substantial change in the body weight occurs during the period of repeated studies. The measurements were made annually. The bone mineral density of the distal radius site was measured using a Lunar Radiation (Madison, Wisconsin) single-photon absorptiometer (SP2). Bone mineral density of the spine (L2-L4) and femur (neck, trochanter, and Ward triangle) was measured using a Lunar Radiation DP4 dual-photon absorptiometer. The software version used for the analysis of scans was DP4 Lunar Corporation Version 1.1. All scans were analyzed using the same software version, which corrects for source decay. Instruments were calibrated daily, and the radioactive source was changed annually. Each measurement was done every 6 months. The coefficient of variation of these measurements was 2%, except for the Ward triangle (2.5%). Activity was measured using activity monitors (large-scale integrated monitors), which were worn about the waist [27]. The average of 2 weekdays and 1 weekend day was used as an activity score. Activity was measured at baseline and at one other point during the study to ensure that differences among the groups were not due to varied levels of exercise. Statistical Analysis Total body calcium was selected as the primary criterion for efficacy for the following reasons: It measures mass rather than density per unit area; it measures calcium balance precisely and accurately in the free living state and may be better related to previous studies using the balance technique; it is more precise than the other measurements; and it avoids sampling error by measuring the entire skeleton rather than a specific region of the appendicular or axial skeleton. The rate of change in bone mineral was calculated for each woman at each of the sites used in the study. Standard linear regression procedures were used to estimate the rate of bone mineral change for each woman, and the regression intercept was used as the best estimate of the baseline value. Because some women terminated their participation in the study before others, the rate-of-change data were weighted by the inverse variance to reflect the fit of the regression line for each woman [28]. Analyses of covariance were done using body mass index, activity scores, cigarette smoking, calcium intake, age, and years postmenopause as covariates. The data reported in this article are based on all women who provided at least three observations for a particular skeletal site. We considered other criteria, such as using data only from women who had participated in the study for at least 2 years, and all data analyses were done for this subgroup as well. The results of these analyses were invariably similar to those reported here and therefore are not presented separately. The mean rates of change in bone mineral for each condition at each site were characterized in terms of both raw units and percentages; separate analyses were carried out for each. The two indices were similar. Evidence from recent research is substantial that estrogen replacement therapy is effective, whereas the efficacy of calcium supplements is questionable. Our expectation was that our data would confirm the efficacy of estrogen-progesterone-calcium therapy, and the critical question was whether or not a beneficial effect of calcium supplements given alone could be shown. A separate one-way analysis of covariance was done for each of the bone mineral measurements to compare the mean rates of change in bone mineral for each of the three conditions. We used two a priori contrasts: the first contrasting women taking estrogen with those receiving calcium and the second comparing women receiving calcium supplements with those on placebo. All P values reported are two-tailed. Results Baseline data for historical data and bone mineral measurements and chemical studies are given in Table 1. Analysis of variance showed no significant differences in the baseline variables. The initial and final activity scores did not differ significantly. Table 1. Baseline Values for Patient Characteristics, Bone Mineral Measurements, and Chemical Variables The range of initial daily calcium intake in the overall study group was 150 to 1263 mg; in the calcium augmentation group, it was 222 to 806