The Journals of Gerontology Series A: Biological Sciences and Medical Sciences 55:M141-M146 (2000)
© 2000 The Gerontological Society of America
Maintenance of Bone Density
Outcomes Over Five Years of Attendance at an Osteoporosis Center
Margaret G. E. Petersona,
Theresa Galsworthyb,
Joseph Lanec,
Patricia L. Wilsonb,
Judith Wingateb,
Diane Lapianob and
Judith Andarieseb
a Department of Biomechanics and Biomaterials, Hospital for Special Surgery, New York City
b The Osteoporosis Prevention Center, Hospital for Special Surgery, New York City
c Department of Orthopaedic Surgery, Hospital for Special Surgery, New York City
Margaret G. E. Peterson, Hospital for Special Surgery, 535 East 70th Street, New York, NY 10021 E-mail: petersonm{at}hss.edu.
William B. Ershler, MD
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Abstract
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Background. This is a longitudinal analysis of the data from women who visited the Osteoporosis Prevention Center for at least five years. The study is part of an ongoing evaluation of the results of the Center visits.
Methods. A random sample of 100 women who had attended the clinic for more than five years and were not referred for a definite medical diagnosis was pulled from the records. Descriptive statistics were compiled on this sample. Seventy-five women were postmenopausal and over 49 years of age. This subgroup was studied for change in bone mineral density (BMD) over the five years.
Results. The BMD change was 0.03 gm/cm2 in the spine, -0.01 gm/cm2 in the femoral-neck, and -0.008 gm/cm2 at the radius over the five years.
Conclusion. Attendance at the Osteoporosis Prevention Center was associated with maintenance of bone density in the spine over a five-year period.
OSTEOPOROSIS affects 24 million Americans, places people at an increased risk for fractures, and will become an ever-increasing problem as the population ages (1). There are many studies identifying the risk factors for osteoporosis, such as family history, low calcium intake, and prolonged steroid use (2)(3)(4). Naturally there is increasing interest in preventing osteoporosis or increasing bone density at any age in life (5)(6)(7). It has been estimated that postmenopausal women lose bone at the rate of 8% per decade for the iliac crest (8), 1% per year for the radius, and 0.5% per year for the lumbar spine (9). This study examines the outcomes of attendance over five years for women at the osteoporosis clinic at the Osteoporosis Prevention Center, Hospital for Special Surgery, New York City.
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Methods
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The Osteoporosis Prevention Center is an early detection center that provides bone mass measurements and individual counseling for people at risk for developing osteoporosis. Most clients are women who are self-referred, are concerned about osteoporosis, and are at some risk for acquiring it. Clients referred for medical reasons are not included in this study. The medical reasons include such conditions as hyperparathyroidism and osteoporosis secondary to treatment for a chronic disease. Those whose bone densities are very high are less likely to make more than one visit. Therefore, those who maintain attendance over five years are more likely to be at risk for osteoporosis.
Selection.
The largest files were pulled at random until 100 were found that met the following criteria. The files were of women who were not referred for medical reasons, had attended the Center over at least a five-year period, and had bone density measurements made on the same equipment (Lunar DPXL, Lunar, Madison, WI), over that five-year period. Data from the beginning, Time 1, and end of the period, Time 2, were collected for the study. Intervening visits were ignored unless data (such as weight) were missing from the visit of interest. Visits are not evenly spaced, because many people do not attend regularly. The return visits were dependent on many factors including the client's lifestyle, the risk factors identified, the actual bone mineral density, and the client's wishes. All visits occurred between 1989 and 1997. Time 2 occurs between 1994 and 1997 inclusive for each person.
Bone mineral density measurement.
Bone mineral density (BMD) is measured in gm/cm2 throughout by the Lunar DPXL. Quality control measurements are run daily and an external phantom is used. Although the Lunar DPXL was used for both measurements, the operators were probably not the same. This introduces an additional random effect for which there is no control in a normal nonexperimental setting. Accuracy measurements have previously been reported on the machine, and are 1.8% in the spine and 2.6% in the femoral neck (10). The measurements were made at the lumbar spine L1–L4, the femoral neck, and the radius 1/3. The ulna was also measured, but those measurements are not discussed here. The measurements were compared to two standard control groups for measurements on that machine (normal referent database for densitometer manufacturer): age-matched healthy peers and 35-year-old normal women assumed to be close to peak bone mass.
Counseling–education sessions.
The counseling–education sessions take place when the results of the BMD measurement are available. The factors discussed are diet, including calcium and vitamin D, exercise, and preventative medications. Optimal calcium intake is set at 1000 to 1500 mgm and vitamin D at 400 iu, daily. The calcium is judged inadequate if less than 50% of the USRDA (i.e., 500 mgms) is ingested, including dietary sources. Exercise is recommended to be at least a formal exercise or general conditioning program, 45 minutes three times a week. Exercise is inadequate if there is no formal program and the client has only incidental walking and general housekeeping or gardening. Preventative medicines such as estrogen and, recently, alendronate are discussed. At return visits, the repeat BMD results and adherence to bone maintenance strategies are reviewed. Further recommendations are made, based on the new results as indicated. If osteoporosis is identified, all therapies are reviewed and a metabolic bone workup is done.
The clinic is self-supporting, with the women paying for the consultation. No grants or institutional funds have been used since 1989, when the startup period was completed.
Analysis.
The data were transferred from a computerized database to SPSS for analysis. For the descriptive comparisons, the unadjusted p value is given. The alpha level was set at 0.05 for the main analysis. Nonparametric analyses were performed on most variables, as the distributions were skewed. Values are reported as mean ± standard deviation. The vitamin D data were not analyzed because of the difficulty of quantifying the dose. ERT therapy was defined as any estrogen therapy.
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Results
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Total sample.
At Time 1, the average age was 59.5 ± 9.1 years. The other Time 1 demographic data for the 100 participants are shown in Table 1 . The age at menopause was 48.8 ± 4.6 years, 
. The average time between Times 1 and 2 was 5.5 ± 1.0 years. None of the women reported using other osteoporosis treatment agents (e.g., bisphosphonates or calcitonin).
The bone density data are shown in Table 2 and Fig. 1. The changes between Time 1 and Time 2 were small and were compatible with the theory of a random distribution with a mean of zero. The BMD changes were measured by subtracting Time 1 values from Time 2, so that a negative change is bone loss over the time interval. At Time 1, bone density measurements of the femoral-neck and spine were associated with one another: a high femoral-neck bone density indicated a high spine bone density, and vice versa 
. Femoral-neck and spine bone densities were associated with the person's height and weight 
; heavier or taller people had better bone density. The bone density at Time 1 was inversely associated with the person's age 
; older people tended to have lower bone density. The radial bone density had an even stronger inverse association with age 
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Figure 1. Bone density in gm/cm2 at (A) the femoral-neck and (B) the spine. Density at Time 1 is the closed diamond, density at Time 2 is the open symbol.
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The change in bone density at the spine was associated with the change at the femoral-neck 
; those with greater change at the femoral-neck tended to have greater change at the spine. The loss of bone density at the femoral-neck was greater for those with greater femoral-neck bone density at Time 1 . The changes in the radius correlated inversely with the value of the bone density at this location at Time 1 
; those with higher density lost more.
In going from Time 1 to Time 2, ERT use doubled; 20 people were taking ERT at Time 1 and 44 people were taking ERT at Time 2 
. This included five people who stopped taking ERT and 29 people who started to take ERT between Time 1 and Time 2. The data for those over 49 years of age are shown in Table 3 . The differences among the groups of women who never took, always took, stopped or started estrogen are not statistically significant. All groups lost bone density at the femoral-neck. Those who stopped taking estrogen had lower bone density than the other groups and were the only group to lose at the spine. However, this is a very small group. At Time 1, 56 people were judged to have an adequate calcium intake; by Time 2, 89 had an adequate dietary and/or supplemental calcium intake.
The values of bone density at Time 1 and the change to Time 2 as a factor of age are shown in Fig. 2. The change in bone density is not a factor of age and in most cases lies close to zero. In the femoral-neck, the density at Time 1 does show a decrease with age.
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Figure 2. Bone density in gm/cm2 at (A) the femoral-neck and (B) the spine as a factor of age. The closed diamonds are bone density at Time 1, the open symbols are the change (Time 2–Time 1).
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Subset: postmenopausal and over 49 years of age.
The analysis was then limited to those over 49 years of age who were postmenopausal 
. The spine bone density went from 0.93 ± 0.16 to 0.96 ± 0.17 in this group, a gain of 0.03 gm/cm2 with a 95% confidence interval (CI) of 0.01 to 0.05. At Time 1, the average compared with their peers was 92% and at Time 2 it was 98%, 80% of 35-year-old normal subjects. The femoral-neck bone density went from 0.73 ± 0.11 to 0.72 ± 0.11 in this group, a loss of -0.01 gm/cm2 with a 95% CI of -0.03 to -0.00002. At Time 1 the average compared with their peers was 96%; at Time 2 it was 90%, 72% compared with 35-year-old normal subjects. The radius lost 0.008 gm/cm2 with a 95% CI of -0.02 to 0.004. ERT use increased in this group: 18 took ERT at Time 1, whereas 29 took ERT at Time 2 
Four women stopped taking ERT. The differences among the groups of women who started, stopped, never took, or always took estrogen were not statistically significant. Fifty-four women were taking supplemental calcium at Time 1; two stopped taking it, but 68 women altogether were taking supplemental calcium at Time 2 (
. Sixty-four women were judged to have adequate exercise at Time 1 and 68 at Time 2.
Regression analysis was done using the predictors identified in the bivariate comparisons. In general, the bone density at Time 2 is predicted by the value at Time 1, 
for femoral-neck and 0.83 for spine. If the value at Time 1 is omitted, age and weight at Time 1 are the predictors for the femoral-neck at Time 2 
, and for the spine 
. There are no predictors of the change in bone density, which is consistent with it being a random effect.
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Discussion
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Older men and women are assumed to lose bone mass. This loss is assumed to occur steadily throughout later life after menopause for women. In Fig. 1 it can be seen that the Time 1 values do not lie uniquely above the Time 2 values, as would be expected if everyone lost bone density. Similarly in Fig. 2, the values lie on rather than below the zero change line. Luckey and colleagues (9) estimated a loss of 0.004 gm/cm2 per year or 0.4% in the lumbar spine of white women who are greater than 5 years postmenopausal. This study finds a gain of 0.03 gm/cm2 or 3% over the 5 years, 0.6%/year. Luckey and associates estimated a loss of 0.006 gm/cm2 per year, or 0.9% in the radius of the same group. This study finds a loss of 0.008 gm/cm2 over the 5 years or 1.3%, approximately 0.3%/year. Mazess (8) estimates a loss of 6% to 8% in trabecular bone (iliac crest) per decade (0.6–0.8% per year), and 3% to 9% per decade in compact bone.
Our earlier study (11) had found no statistically significant decrease over 12–18 months for postmenopausal women who attended the Osteoporosis Prevention Center at least twice. This study extends the time period to at least 5 years and finds a lower rate of loss than either Luckey and colleagues or Mazess. In fact, there is a gain of density recorded in the spine. The loss or gains recorded are within the recorded accuracy of the machine. These women are self-motivated to take care of themselves and most of them started with below-adequate bone density. Over the 5 years, more of them met the requirements of adequate exercise, adequate calcium, and taking estrogens.
This is not to say that the bone density is high enough to prevent fracture or that the bone is of adequate strength, but it does indicate that following advice and taking positive steps to maintain healthy bone mass is associated with maintenance of a constant bone density over a 5-year period to within measurement error. Regression analysis showed that the value at Time 1 was the best predictor of the value at Time 2. Weight is positively correlated with the values for femoral-neck and spine at Time 2. This latter finding is in agreement with the work of Harris and Dawson-Hughes (12), who analyzed body composition for postmenopausal women. Body mass index is positively correlated with the value for the spine at Time 2.
One interesting finding may be unique to this sample. Although having breast fed was associated with bone loss over the 5 years, having breast fed did not appear as a predictor in the regression analysis. However, the bone loss and the number of cases were low, and it was not possible to correct for years since delivery or number of babies fed. It is possible that this is a random effect.
In aggregate, the gains and losses over the 5-year period were small and were not statistically significant. This strongly supports the suggestion that following several simple rules promotes better bone health. This suggests that a comprehensive, focused counseling program and a full explanation of the implications of the bone mass measurements are the impetus needed for these women to implement bone-healthy lifestyles.
Conclusion.
Significant loss of bone mineral density in postmenopausal women is not detected over 5 years if they are motivated to pursue healthy lifestyles and given the information they need to promote healthy bone.
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Acknowledgments
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We dedicate this article to Judy Wingate, RN, a co-author, who died in February 1998.
Received August 11, 1998
Accepted August 10, 1999
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Abstract
Methods
