Timing of Estrogen Replacement Therapy for Optimal
Osteoporosis Prevention
JANE A. CAULEY, JOSEPH M. ZMUDA, KRISTINE E. ENSRUD, DOUGLAS C. BAUER, AND
BRUCE ETTINGER FOR THE STUDY OF OSTEOPOROTIC FRACTURES RESEARCH GROUP
Department of Epidemiology (J.A.C., J.M.Z.), University of Pittsburgh, Pittsburgh, Pennsylvania 15261; Department of Internal Medicine and Epidemiology (K.E.E.), University of Minnesota, Minneapolis, Minnesota 55417; Department of Epidemiology and Biostatistics (D.C.B.), University of California, San Francisco, San Francisco, California 94105; and Kaiser Permanente Medical Care Program (B.E.), Oakland, California 15261
To determine whether estrogen initiated at age 60 yr or later reduces rates of bone loss and fracture incidence, we performed a prospective cohort study of 6910 nonosteoporotic women, 65 yr of age or older. Estrogen use, medical history, lifestyle, and an-thropometric data were obtained by questionnaire, interview and examination. We identified five patterns of estrogen use: never users (67%); past early users (started under age 60 yr with no current use; 23%); past late users (started at age 60 or later with no current use; 2%); current early users (started under age 60 yr with use both at baseline and 6 yr later; 6.7%); and current late users (started at age 60 or later with use at baseline and 6 yr later; 1.5%). Bone mineral density was measured at the total hip twice, an average of 3.5 yr apart, and at the calcaneus, an average of 5.7 yr apart. Incident nonspine fractures were vali-dated by radiographic report. Bone mineral density was
signif-icantly higher among current users, compared with never and past users. The annual rate of hip bone loss was significantly lower in current early users (ⴚ0.22%/yr) and current late users (ⴚ0.35%/yr) in comparison with never users (ⴚ0.6%/yr), past early users (ⴚ0.6%/yr), and past late users (ⴚ0.72%/yr). During an average of 11.0 yr of follow-up, 1953 nonspine fractures were confirmed. The multiple-adjusted relative risk of nonspine frac-ture was 0.63 (95% confidence interval 0.51– 0.78) among current early users and 0.75 (0.50 –1.12) among current late users, com-pared with never users. Early initiation and long-term contin-uation of estrogen is associated with a reduction in the risk of nonspine fractures, and initiation at or after age 60 yr with long-term continuation may also be associated with a reduced fracture risk. (J Clin Endocrinol Metab86: 5700 –5705, 2001)
O
BSERVATIONAL STUDIES HAVE reported lower fracture rates in postmenopausal women who take estrogen than in women not receiving this therapy (1–5). Addition of a progestin has little effect on the observed fracture benefit (1). Previous analyses from the Study of Osteoporotic Fractures suggested that for optimal preven-tion of fractures, estrogen therapy should be initiated within 5 yr of menopause, even among women who had used es-trogen for more than 10 yr (1). These data imply that women need to continue their estrogen initiated soon after meno-pause for their remaining lifetime to prevent osteoporosis, raising a concern about breast cancer and other risks asso-ciated with extended use of estrogen (6).Schneideret al.(7) subsequently reported that women who initiated estrogen after age 60 yr and continued had similar bone mineral density (BMD) as women who started their estrogen before age 60. In addition, despite accelerated rates of bone loss among women over age 80 yr, elderly women taking estrogen experienced significantly slower rates of bone loss than women not on estrogen (8).
These results raise the possibility that women could delay initiation of estrogen for prevention of osteoporotic fractures. However, before such a recommendation can be made, in-formation is needed on whether delaying initiation of estro-gen will influence the risk of fractures. In the current report,
we expanded our initial analyses of the Study of Osteopo-rotic Fractures (SOF) cohort to include an additional 6.5 yr of follow-up to test the hypothesis that estrogen initiated at age 60 yr or later will result in a reduced risk of fractures.
Materials and Methods Subjects
All women were participants in the SOF, a prospective study of 9704 community-dwelling white women who were at least 65 yr of age. Women were recruited for SOF between 1986 and 1988 from population-based listings, such as voter registration lists, at four clinical centers in the United States: Baltimore, MD; Minneapolis, MN; Mon Valley, PA; and Portland, OR (9). Women were excluded from the study if they reported a bilateral hip replacement or were unable to walk unassisted. African-American women were excluded because of their low risk of hip fracture. The institutional review boards at each institution approved the study. All women provided written informed consent at entry into the study and at each clinical examination.
Because this report focused on prevention of fractures, we excluded 1907 women who reported a history of physician-diagnosed osteopo-rosis or spine fracture at baseline and 175 women who had missing information on their history of osteoporosis. We excluded women who reported estrogen use more than 2 yr before the onset of menopause and women with missing information on age at menopause or estrogen use at baseline or at the follow-up visit. Because of accelerated bone loss after discontinuation of estrogen (10), we excluded 189 women who reported estrogen use at baseline but had discontinued use by the follow-up examination. Thus, the current analysis is based on 6910 women enrolled in the SOF cohort.
Estrogen/Progestin
Information on estrogen and progestin use was obtained during a clinic interview at baseline and 6 yr later. Participants were asked to Abbreviations: BMD, Bone mineral density; BMI, body mass index;
HERS, Heart and E/progestin Replacement Study; SOF, Study of Os-teoporotic Fractures.
bring all medications to the clinic for verification of use, preparation, and dosage. Information was collected about oral and parenteral (skin patches, injections, vaginal creams, and suppositories) and oral proges-tins. Our analyses are limited to oral preparations. Data were collected on age at initiation of use of hormone preparations and on whether a participant had used such preparations for the entire time period and, if not, when she had stopped. Duration of use was calculated by adding up the total number of years that a woman had used estrogen. Estrogen users included women who reported combination estrogen and pro-gestin use.
We identified five patterns of estrogen use, adapted from the Rancho-Bernardo study (7). These five patterns of use included: never users; past early users (women who initiated estrogen use before age 60 yr but discontinued its use before baseline); past late users (women who ini-tiated estrogen use at age 60 yr or greater but discontinued its use before baseline); current early users (women who initiated use before age 60 yr and were taking estrogen at both baseline and 6 yr later); current late users (women who initiated estrogen use at age 60 yr or greater and were taking estrogen at both baseline and 6 yr later).
BMD
Distal and proximal radial and calcaneal BMD was measured using single-photon absorptiometry using the Osteon Osteoanalyzer (Dove Medical Group, Los Angeles, CA). The measurement of calcaneal BMD was repeated an average of 5.7 yr later using single x-ray absorptiom-etry. Lumbar spine and total hip BMD (and subregions) were measured by dual-energy x-ray absorptiometry using the QDR 1000 (Hologic, Inc., Bedford, MA). The measurement of total hip subregion BMD was re-peated an average of 3.5 yr later. Details of these methods and quality control procedures have been reported elsewhere (8, 11). Bone loss is expressed as an annualized percentage change in BMD.
Other measurements
Body weight was measured (after removal of shoes and heavy outer clothing) using a balance beam scale. Height was measured without shoes using a Harpenden stadiometer (Holtain Ltd., Dyved, UK). Height and weight were used to calculate the body mass index (BMI, kg/m2).
Radial pulse rate was measured in the supine position after 5 min of rest. Reported health status, reproductive history, alcohol consumption, and physical activity were assessed by questionnaire that was reviewed with the participant by a trained interviewer. The measure of alcohol con-sumption was expressed as drinks per week adjusted for atypical drink-ing, especially heavy drinking during the previous 30 d. Dietary calcium intake was assessed by a food frequency questionnaire and by interview using standardized food models to estimate portion sizes (12). Total calcium intake included dietary and supplemental calcium. Women were asked whether they walk for exercise. Women were also asked about whether they were currently taking thiazide diuretics, thyroid hormones, or corticosteroids.
Ascertainment of fractures
Details of our method for identifying fractures have been published (13). Briefly, we contact participants every 4 months by postcard or telephone to ask whether they had sustained a fracture. More than 95% of these contracts were completed. All fractures are confirmed by ra-diographic report or by x-ray (hip fracture). We excluded fractures that occurred because of major trauma such as motor vehicle fractures as well as face and skull fractures. Most vertebral fractures do not come to medical attention. These fractures must be discovered by systematically obtaining radiographs from all participants and by comparing them with previous radiographs. Hence, self-reported vertebral fractures were not included.
Follow-up for fractures averaged 11 yr, range 0.02–13.9 yr. For women who died during the follow-up period, date of death was used as the end of follow-up.
Statistical analyses
We compared the characteristics of the women, BMD, and annual percent change in BMD across patterns of estrogen use by ANOVA or
analysis of covariance for continuous variables and2tests for
categor-ical variables. Incidence rates of fracture were calculated for each pattern of estrogen use by dividing the number of fractures by the number of person-years of follow-up and multiplying by 1000. Cox proportional hazard models were used to assess the relationship between pattern of estrogen use and nonspine fractures first after adjusting for age and BMI and subsequently after adjusting for multiple covariates including: age, BMI, physical activity (walk for exercise), current use of steroids, thyroid hormones and thiazide diuretics, total calcium intake, history of bilateral oophorectomy, and alcohol consumption (three or more drinks per week
vs.not). Additional adjustment was made for health status and pulse rate. We calculated the relative risk of fracture and 95% confidence intervals. Women who had never used estrogen formed the referent group. To test the hypothesis that bone mass accounts for the effect of estrogen on fracture risk, we subsequently added total hip BMD to the multivariate models.
In a separate analysis, we further excluded women who had osteo-porosis at the total hip as defined by the World Health Organization:t
score ⫺2.5 or lower (14). We examined the relative risk of nonspine fracture across patterns of estrogen in these nonosteoporotic women, (n⫽4517).
Results
Sixty-seven percent of the 6901 women included in this analysis had never used estrogen; 23% were past early users; 2%, past late users; 7%, current early users, and 1.5%, current late users (Table 1). Never users were on average 2–3 yr older than the E-using women. The average duration of estrogen use was 5 yr among past early users; 2 yr among past late users, 25 yr among current early users, and 10 yr among current late users. The average interval between onset of menopause and initiation of estrogen was considerably shorter among the early users, averaging about 2 yr. In con-trast, initiation of estrogen in the late users was on average 16 –19 yr after the onset of menopause.
Consistent with previous studies on selection factors for es-trogen use, current users had a lower BMI than past or never users and a higher percentage reported walking for exercise. Total calcium intake was higher among women who had ever used estrogen in comparison with never users. Current late users reported significantly greater calcium intake than current early users. The average radial pulse rate was lowest in current early users. Current early and late estrogen users were similar except that almost 50% of current early users reported a bilateral oophorectomy, compared with about 20% in current late users. A higher percentage of current early and late users reported use of thyroid hormone in comparison with never and past users, but there was no difference in use of steroids or thiazide di-uretics across estrogen use. The overall prevalence of cigarette smoking was lowest among current late users, but there was no significant difference across pattern of estrogen use. Alcohol consumption varied substantially across pattern of estrogen use with the lowest consumption among never and current late users and the highest consumption among past late users. The percent of women who reported fair or poor health status was lowest among past late users, but there was little difference across the remaining groups.
BMD
Multivariate adjusted BMD levels across pattern of estro-gen use are shown in Table 2. Women who started estroestro-gen before age 60 yr and continued (current early users) had the highest BMD at every site, compared with all other groups.
Compared with never users, current early users had 13% higher mean BMD at the total hip, 9% higher BMD at the femoral neck, 15% higher at the lumbar spine, 13% higher BMD at the prox-imal radius, 17% higher BMD at the distal radius, and 15% higher BMD at the calcaneus. Thus, in comparison with never users, their BMD was on average 0.5–1.0sdhigher.
Women who reported current use of estrogen but initiated use at age 60 or later (current late users) also had significantly higher BMD than never users. Compared with never users, their total hip BMD was 8% higher; femoral neck, 5% higher; lumbar spine, 7% higher; proximal radius, 6% higher; distal radius, 8% higher; and calcaneus, 10% higher. The magni-tude of the difference in BMD between current late users and never users was about 0.3– 0.5sdhigher.
BMD was significantly higher among current early users, compared with current late users. The percent difference in BMD between these two groups of estrogen users ranged from a low of 2% for the femoral neck to a high of 8% for the lumbar spine and distal radius.
In general, BMD was similar in both early and late past users and never users. At some sites, the difference was
statistically significant, but the magnitude of the difference was quite small.
Bone loss
The annual percentage change in total hip BMD and cal-caneal BMD by pattern of estrogen use is shown in Fig. 1 and Fig. 2. The annual rate of bone loss was significantly slower among women who reported current estrogen use in com-parison with past or never users. There was no difference in the rate of bone loss among current users who initiated use at age 60 yr or later and continued (⫺0.35% per year, total hip BMD) and women who initiated use before age 60 and con-tinued (⫺0.22% per year, total hip BMD). Similar results were observed for calcaneal BMD. Additional adjustment for health status and pulse rate had no effect on our results (data not shown).
Nonspine fractures
There was no evidence that past use of estrogen was pro-tective against fractures, Table 3. Women who started estro-TABLE 1. Characteristics of women across pattern of estrogen use
Characteristic Never use Past early Past late Current early Current late Pvalue
n (%) 4630 (67) 1579 (23) 131 (1.9) 466 (6.7) 104 (1.5) —
Age (yr) 72.2⫾5.6 70.4⫾4.3a 72.8⫾6.0b 69.4⫾3.7a,b,c 70.3⫾4.3a,c 0.0001
Duration of ERT (yr) — 5.1⫾6.0 1.9⫾3.4b 24.9⫾8.3b,c,d 9.7⫾4.2b,c 0.0001
Interval between ERT initiation and menopause (yr)
— 1.6⫾3.8 16.6⫾8.6b 2.3⫾4.4b,c,d 18.9⫾7.8b,c 0.0001
BMI (kg/m2) 26.9⫾4.8 26.3⫾4.5a 26.5⫾4.9 25.3⫾3.9a,b,c 25.2⫾3.8a,b,c 0.0001
Age at menopause (yr) 47.2⫾6.2 46.6⫾5.9a 48.9⫾6.2a,b 45.6⫾6.6a,b,c,d 47.7⫾5.8 0.0001
Calcium intake (mg/d) 953⫾673 1103⫾688a 1143⫾628a 1172⫾845a,d 1461⫾845a,b,c 0.0001
Pulse rate (beats/min) 69.5⫾10.0 68.5⫾9.9a 67.2⫾9.2a 66.9⫾9.2a,b 67.8⫾11.8 0.0001
Walk for exercise (%) 47.6 55.3 54.2 58.3 62.5 ⬍0.001
Alcohol (%ⱖ3 drinks/wk) 17.3 22.4 28.2 26.4 17.3 ⬍0.001 Smoke cigarettes (%) 9.4 11.3 9.2 9.9 6.7 0.21 Thyroid hormone (%) 10.0 12.7 8.5 15.4 13.6 ⬍0.001 Steroids (%) 1.5 1.5 1.6 2.0 2.9 0.81 Thiazide diuretics (%) 26.8 23.5 28.5 26.9 25.0 0.13 Bilateral oophorectomy (%) 10.3 23.8 16.0 44.6 21.2 ⬍0.001
Health status (% fair/poor) 15.2 12.9 6.9 11.5 12.2 0.005
Plus minus values are standard deviations. ERT, Es replacement therapy. aP⬍0.05vs.never users.
bP⬍0.05vs.past early users. cP⬍0.05vs.past late users. dP⬍0.05vs.current late users.
TABLE 2. BMD (g/cm2) across pattern of estrogen usea
Never use Past early Past late Current early Current late
Proximal femur
Total hip 0.75⫾0.13 0.77⫾0.12 0.76⫾0.13 0.85⫾0.13b,c,d,e 0.81⫾0.14b,c,d
Femoral neck 0.65⫾0.11 0.66⫾0.10b 0.64⫾0.11 0.71⫾0.12b,c,d,e 0.68⫾0.12b,c,d
Lumbar spine 0.85⫾0.17 0.87⫾0.16b 0.87⫾0.19 0.98⫾0.18b,c,d,e 0.91⫾0.16b,c,d
Radius
Proximal 0.63⫾0.10 0.64⫾0.10b 0.64⫾0.10 0.71⫾0.08b,c,d,e 0.67⫾0.09b,c,d
Distal 0.36⫾0.08 0.37⫾0.08b 0.37⫾0.09 0.42⫾0.08b,c,d,e 0.39⫾0.08b,c,d
Calcaneus 0.40⫾0.09 0.41⫾0.09b 0.42⫾0.11b 0.46⫾0.09b,c,d,e 0.44⫾0.09b,c,d
aAdjusted for age, BMI; calcium intake; walk for exercise; cigarette smoking; use of thyroid hormone, thiazide diuretics, or steroids; alcohol consumption, and history of bilateral oophorectomy. Mean⫾SD.
bP⬍0.05vs.never users. cP⬍0.05vs.past early users. dP⬍0.05vs.past late users. eP⬍0.05vs.current late users.
gen use before age 60 yr and continued had the lowest rate of fracture. In multivariate analyses, their risk of any non-spine fracture was reduced by 37% (20 – 49%) in comparison with never users. Compared with never users, women who initiated estrogen use at age 60 or later had a statistically nonsignificant 25% reduction in the risk of nonspine frac-tures. Additional adjustment for health status and pulse rate had no effect on our results (data not shown). In analyses limited to women without osteoporosis as defined by their total hip BMD, our results were similar: The relative risk of nonspine fracture among women who initiated use at age 60 or later and continued long term was 0.61 (95% confidence interval, 0.37–1.02). Inclusion of total hip BMD in the mul-tivariate models attenuated the effect of estrogen on fracture risk in both current early and late estrogen users.
Discussion
Current estrogen users who initiated use before age 60, an average of 2 yr within menopause and had an average duration
of use of 25 yr, had the highest average radial, calcaneal, hip, and lumbar spine BMD, experienced the lowest average rate of bone loss, compared with all other women, and had a 37% lower risk of experiencing a nonspine fracture, compared with women who had never used estrogen. These findings are con-sistent with our previous report, which demonstrated that for optimal prevention of fractures, estrogen should be initiated within 5 yr of menopause and continued (1).
However, we also found that women who initiated estro-gen use at age 60 or later, an average of almost 20 yr after the onset of menopause and who continued for an average of 10 yr, tended to have nonspine fracture rates lower than never or past users. Failure to reach statistical significance may have reflected the smaller sample of women who initiated estrogen many years after menopause. However, these re-sults suggest that initiation of estrogen well beyond the menopause transition can still be effective in reducing frac-ture risk. This conclusion differs from our previous results that were based on a considerably shorter period of follow-up for fracture. In our earlier report, we found no fracture benefit among women who had used estrogen for at least 10 yr but had initiated use more than 5 yr after meno-pause (1). The current report extends follow-up for an ad-ditional 6.5 yr, increasing our power to detect a benefit among these women.
Later initiation would reduce the overall duration of es-trogen use, lowering other health-related consequences of long-term use of estrogen. This could impact on the risk-benefit equation when evaluating estrogen replacement ther-apy in older women.
Our results are consistent with the findings of the Rancho-Bernardo cohort, which first reported that women who ini-tiated use at age 60 yr or later and continued use had higher BMD than women who had used estrogen in the past or had never used estrogen. Our results extend these findings to include slower rates of bone loss and possibly fracture ben-efits among these late initiators of estrogen. Our results are also consistent with the model developed by Ettinger and Grady (15) that initiation of estrogen at age 65 would result in an improvement in bone mass and a reduction in fractures. The relative risk of nonspine fracture was attenuated when we adjusted for total hip bone mass, which is consistent with the hypothesis that estrogen prevents fractures by preserving bone mass.
The major limitation to our study is its observational de-sign. Observational studies may be biased because women who use estrogen therapy are healthier, of a higher social class, have access to medical care, and are more compliant and maintain healthier lifestyles than women who do not use estrogen (16). We controlled for many factors that differ markedly across the patterns of estrogen use, but there may be residual confounding by other factors we did not measure. Only a randomized trial can provide conclusive evidence that estrogen causes a reduction in fractures.
There have been few controlled, randomized trials of es-trogen with fracture as an end point. A recent metaanalysis of hormone replacement therapy and the prevention of non-vertebral fractures concluded that hormone therapy was ef-fective in reducing fractures among women under age 60 yr but not among older women (17). However, an accompany-FIG. 1. Annual percentage change in total hip BMD across pattern of
estrogen use. Analyses adjusted for age, BMI, calcium intake, walk for exercise, cigarette smoking, use of thyroid hormone, thiazide diuretics or steroids, alcohol consumption, and history of bilateral oophorec-tomy. Mean⫾SEare shown.
FIG. 2. Annual percentage change in calcaneal BMD across pattern of estrogen use. Analyses adjusted for age, BMI, calcium intake, walk for exercise, cigarette smoking, use of thyroid hormone, thiazide di-uretics or steroids, alcohol consumption, and history of bilateral oo-phorectomy. Mean⫾SEare shown.
ing editorial noted that this conclusion was based on essen-tially one study among younger subjects and one study, among older subjects, the Heart and E/progestin Replace-ment Study (HERS) (18).
HERS was the largest randomized trial of hormone re-placement therapy. Results showed that 4 yr of treatment with hormone replacement therapy did not reduce the in-cidence of fractures among these 2763 women, mean age 67 yr, with heart disease (19). The difference between results of the current report and the HERS trial may reflect the much longer duration of use in our study, even among women who initiated use after age 60 (average duration of use, 10 yr). Results from the Framingham study suggested that women need to take estrogen for at least 7 yr after menopause (20). There were also important differences between the char-acteristics of the women in HERS and SOF that also may have contributed. Most notably, the HERS women all had coro-nary heart disease. Hysterectomized women were excluded from HERS, so our results are not directly comparable, es-pecially because hysterectomy status was a major selection factor for estrogen use (16). In addition, the women in HERS were on average more obese than the women in the SOF cohort.
We found that estrogen was effective in preventing bone loss, irrespective of when it was initiated. These results are consistent with observational studies (10, 21) and clinical trials (19, 22) that antiresorptive agents are effective in re-ducing bone loss in elderly women.
Our study confirms that previous use of estrogen does not have long-standing effects on BMD, bone loss, or fractures (1, 7). Women who initiated use an average of 1.6 yr after the onset of menopause and continued use for about 5 yr had similar BMD, rates of bone loss, and fracture risk as women who never used estrogen. Failure to see any benefit among these women may reflect accelerated loss of bone following discontinuation of therapy (10). The small group of past-late estrogen users took estrogen for less than 2 yr about 16 yr ago on average and it is not surprising that such short-term use decades ago had no impact on fractures. Many women ini-tiate therapy around menopause for relief of menopausal symptoms and discontinue its use once the symptoms have abated. It will be important to evaluate whether these women achieve fracture benefits if they restart their estrogen later in life.
The focus of our study was osteoporosis prevention. To this end, we relied on a self-report of a physician diagnosis of osteoporosis or spine fracture to exclude women who may have been prescribed estrogen for treatment of their osteo-porosis. We have shown previously that women with a self-report of osteoporosis were more likely to take estrogen (16), but our study may have included some women with osteo-porosis, defined by more objective criteria. However, in a subanalysis, we excluded women who had a total hip BMD
tscore less than or equal to⫺2.5, and our results were similar. There are a number of strengths to our study. The sample size was large enough to facilitate defining several important patterns of estrogen use and to link these patterns with a fracture outcome. All fractures were validated by radio-graphic report. Follow-up for fracture is more than 95% complete, so it is very unlikely that there could be differential reporting of fractures across patterns of estrogen use. Finally, we adjusted for many confounding factors that could have influenced our results.
There are, however, a number of limitations. Our results are limited to older white women, but it is this population that appears to have the greatest risk of osteoporosis and who may benefit most from preventive efforts. The design was observational; randomized trials of hormone therapy that are designed with longer follow-up, such as the Wom-en’s Health Initiative may be useful in addressing the question of whether initiation of use at older ages prevent fractures. Our power to detect fracture risk reduction was limited among women who initiated use at age 60 yr or later and continued. Finally, our primary outcome in-cludes a heterogeneous combination of fractures. Infor-mation on specific types of fractures is needed, although most of the fractures are, indeed, related to low bone mass and are osteoporotic in nature (23).
In summary, women who initiated estrogen before age 60 yr and continued had the greatest BMD, lost less bone, and experienced a 37% lower risk of fracture. Of importance, initiation of use at age 60 or later is also effective in main-taining BMD, slowing bone loss and appears to reduce frac-ture risk. If estrogen can effectively be postponed until a woman is older, we may be able to reduce the overall costs and risks associated with its extended use.
TABLE 3. Incidence rate and relative risk (95% confidence interval) of nonspine fracture across pattern of estrogen usea
Person-years No. of women with fractures
Incidence rateb
Relative risks (95% confidence interval) Age, BMI adjusted Multivariate
adjusted
Multivariate
adjustedc Multivariate and
BMD adjustedd Never users 49,668 1,341 27.0 1.0 1.0 1.0 1.0 Past users Early 17,860 448 25.1 0.99 (0.89 –1.10) 0.95 (0.85–1.07) 1.01 (0.88 –1.15) 1.04 (0.91–1.20) Late 1,416 42 27.0 1.17 (0.86 –1.59) 1.16 (0.85–1.58) 1.12 (0.76 –1.66) 1.13 (0.76 –1.67) Current users Early 5,606 97 17.3 0.66 (0.53– 0.81) 0.63 (0.51– 0.78) 0.68 (0.54 – 0.87) 0.83 (0.65–1.06) Late 1,253 25 20.0 0.79 (0.53–1.17) 0.75 (0.50 –1.12) 0.61 (0.37–1.02) 0.71 (0.42–1.19)
aAdjusted for age; BMI; calcium intake; walk for exercise; cigarette smoking; use of thyroid hormone, thiazide diuretics, or steroids; alcohol consumption; and history of bilateral oophorectomy. Never users form the referent group.
bPer 1000 person-years.
cExclude women with total hip BMDtscoreⱕ⫺2.5; total (n⫽4517). dAdditional adjustment for total hip BMD.
Acknowledgments
Investigators in the Study of Osteoporotic Fractures Research Group— University of California, San Francisco (Coordinating Center): S. R. Cummings (principal investigator), M. C. Nevitt (coinvestigator), D. C. Bauer, (coinvestigator), K. Stone (project director), D. M. Black (study statistician), H. K. Genant (director, central radiology laboratory), P. Mannen (research associate), T. Blackwell, W. S. Browner, M. Dockrell, T. Duong, C. Fox, S. Harvey, M. Jaime-Chavez, L. Y. Lui, G. Milani, L. Nusgarten, L. Palermo, E. Williams, D. Tanaka, C. Yeung. University of Maryland: M. Hochberg (principal investigator), J. C. Lewis (project director), D. Wright (clinic coordinator), R. Nichols, C. Boehm, L. Fi-nazzo, B. Hohman, T. Page, S. Trusty, H. Kelm, T. Lewis, B. Whitkop. University of Minnesota: K. Ensrud (principal investigator), K. Mar-golis (coinvestigator), P. Schreiner (coinvestigator), K. Worzala (coin-vestigator), M Oberdorfer (project director), E. Mitson (clinic coordina-tor), C. Bird, D. Blanks, F. Imker-Witte, K. Jacobson, K. Knauth, N. Nelson, E. Penland-Miller, G. Saecker. University of Pittsburgh: J. A. Cauley (principal investigator), L. H. Kuller (co-principal investigator), M. Vogt (coinvestigator), L. Harper (project director), L. Buck (clinic coordinator), C. Bashada, D. Cusick, G. Engleka, A. Flaugh, A. Githens, M. Gorecki, D. Medve, M. Nasim, C. Newman, S. Rudovsky, N. Watson, D. Lee.
The Kaiser Permanente Center for Health Research, Portland, Ore-gon: T. Hillier (principal investigator), E. Harris (co-principal investi-gator), E. Orwoll (coinvestiinvesti-gator), H. Nelson (coinvestiinvesti-gator), Mikel Aiken (biostatistician), Marge Erwin (project administrator), Mary Rix (clinic coordinator), Jane Wallace, Kathy Snider, Kathy Canova, Kathy Pedula, JoAnne Rizzo.
Received May 31, 2001. Accepted August 23, 2001.
Address all correspondence and requests for reprints to: Jane A. Cauley, Ph.D., University of Pittsburgh, Department of Epidemiology, Pittsburgh, Pennsylvania 15261.
This work was supported by in part by Public Health Service research grants from the NIH: AR35582, AM35584, AG05407, AG05395 and AR35583.
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