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Keywords:

  • bone mineral density;
  • dual- energy X-ray absorptiometry;
  • osteopenia;
  • osteoporosis;
  • prevalence

Abstract

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

Objective:  There are some clues that correct interpretation of bone mineral density (BMD) when measured by dual-energy X-ray absorptiometry (DXA) which requires a population specific reference range. We determined reference values of BMD and the prevalence of osteopenia and osteoporosis in postmenopausal Isfahani women.

Methods:  In this cross-sectional study, 1118 healthy women from Isfahan, aged between 20 and 80 years were recruited door-to-door for research. BMD was measured at the anteroposterior lumbar spine (L2–L4) (AP) and femoral neck (FN) with the Lunar DPX-IQ densitometer. Peak bone mass (PBM), reference curves of BMD, prevalence of osteoporosis and osteopenia were determined according to World Health Organization (WHO) criteria.

Results:  In Isfahani women osteoporosis and osteopenia of the AP lumbar spine exists at BMD < 0.898 g/cm2 and between 1.078 g/cm2 and 0.898 g/cm2, respectively. At the FN a BMD < 0.676 g/cm2 defines osteoporosis whereas osteopenia is defined as a BMD between 0.841 g/cm2 and 0.676 g/cm2. The prevalence of osteoporosis and osteopenia at the AP lumbar spine in the age groups 51–55, 56–60, 61–65, 66–70, > 70 years were, 7.9%, 19.6%, 26%, 32.1%, 31.8%, and 28.9%, 36.5%, 38.4%, 41.1%, 45.5%, respectively. The prevalence of osteoporosis and osteopenia at the FN in the same age groups, were, 2.6%, 2%, 12.3%, 14.3%, 22.7% and 28.3%, 39.9%, 43.8%, 50%, 68.2%, respectively.

Conclusions:  Our data would use a population-specific reference range for DXA measurements and to estimate the prevalence of osteopenia and osteoporosis.


INTRODUCTION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

Osteoporosis is the most common metabolic bone disease, characterized by decrease in bone mass and deterioration of bony micro-architecture resulting in an increased susceptibility to fracture.1 Dual-energy X-ray absorptiometry (DXA) is the most commonly used technique in measuring bone mineral density (BMD) in the diagnosis of osteoporosis. BMD has been related to many factors including heredity, race, region, environment, nutrition, lifestyle, and so on.2–6

A panel convened by the World Health Organization (WHO) defined osteoporosis in terms of BMD as measured by DXA. The panel suggested that osteoporosis is a BMD 2.5 SD (T-score ≤ –2.5) or more below peak bone mass (PBM), which itself was defined as the average maximum bone mass achieved by young healthy sex- and race-matched adults.7 Osteopenia, a reduction of bone mass with an increased risk of osteoporosis, is defined as a BMD between 1.0 and 2.5 SD below PBM (T-score between –1.0 and –2.5). These criteria are now generally applied to populations at risk and are very frequently used to confirm a diagnosis of osteoporosis and to estimate fracture risk.8,9

To determine the reference curves of BMD versus age at various skeletal sites in Isfahani women and to establish the appropriate reference curves for the diagnosis of osteoporosis, we measured the BMD at the anteroposterior lumbar spine (L2–L4) and femoral neck with the Lunar DPX-IQ densitometer, in a population of 1118 healthy native Isfahani women and constructed reference curves for the diagnosis of osteoporosis.

SUBJECTS AND METHODS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

One thousand one hundred and eighteen healthy women from Isfahan, age between 20 and 80 years were receriuted door-to-door for research purposes, from February 2006 to September 2006. The subjects were selected by multistage cluster sampling. We designed a two-stage sampling: in the first cluster sampling, there were 13 clusters. We then divided the total sample size by the number of clusters (1118/13). We prepared a sample frame, and chose 86 subjects from each cluster by a systematic method.

All subjects were screened by a detailed questionnaire, history and physical examination. Subjects were excluded if they had a history of conditions that affect bone metabolism, such as: diseases of the kidney (chronic renal failure, urolithiasis); liver and gastrointestinal (cirrhosis, malabsorption syndromes, gastrectomy and intestinal bypass); endocrine (parathyroid, thyroid, hypogonadism, diabetes mellitus); menstrual abnormality; rheumatic and bone mineral diseases (rheumatoid arthritis, systemic lupus erythematosus, ankylosing spondylitis); malignancy; hematologic diseases, previous pathologic fractures; pregnancy; lactation; immobilization; smoking; ever-use of any of the following medications: steroid, estrogen, anticonvulsants, sodium fluorides, anticoagulants, prolonged or excessive thyroid replacement therapy, vitamin D or calcium. BMD of the anteroposterior lumbar spine (vertebrae L2–L4) and the-non-dominant femur was done in 1118 healthy Isfahani women. The BMD, expressed in grams per square centimeter, was measured by the Lunar DPX-IQ densitometer. The patient was asked to lie supine and scans of the lumbar spine and non-dominant femur were obtained. The in vivo reproducibility for the lumbar spine and femoral neck was 1%. Machine calibration using the phantom scan was done daily prior to doing any scan to ensure precision of the machine. All subjects had their body height and weight measured using a stadiometer and standardized balance beam scale, respectively. This study was accepted by the regional ethical committee. All subjects gave their informed consent.

Statistical analyses

SPSS version 11.5 was used for statistical analysis. BMD at various sites in subjects with age-related changes was evaluated and the best-fit model found by a comparison of different regression models: the linear, logarithmic, quadratic, cubic, compound, power, growth, and exponential equations. All subjects were stratified in 10-year increments and the BMD results reported as the mean and standard deviation (SD) at various skeletal regions, body weight, body height and BMI in each group. The peak BMD was determined from the age group with the highest mean BMD value, and outliers of more or less than 3 SDs beyond the mean peak BMD were excluded from the database. The PBM was determined from the age group 20–29 years. The prevalence of osteoporosis and osteopenia at each skeletal site were calculated using the WHO panel's definition of osteoporosis and osteopenia.7 In each case the PBM was used for calculating T-scores in women. Differences in the peak BMD among Isfahani women and Caucasian women were determined by one-sample t-test. The cubic regression model was performed on the means of BMD for various age groups to establish the changing curves of BMD. Chi-square test was used between women with osteopenia, osteoporosis and normal BMD. P-values < 0.05 were considered statistically significant.

RESULTS

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

The age distribution in 10-year increments and anthropometric features of the population of 1118 healthy Isfahani women are detailed in Table 1. The mean BMD and corresponding SD at each site are shown in Table 2. Based on these results the PBM of the AP lumbar spine and femoral neck for Isfahani women is defined as the mean BMD of the AP lumbar spine and femoral neck in the age group 20–29 years. According to the WHO criteria, in Isfahani women osteoporosis of the lumbar spine exists at a BMD of < 0.898 g/cm2. Osteopenia of the lumbar spine exists at BMD between 1.078 g/cm2 and 0.898 g/cm2. For the femoral neck a BMD < 0.676 g/cm2 defines osteoporosis whereas osteopenia is defined as a BMD between 0.841 g/cm2 and 0.676 g/cm2. The BMD decreases with increasing age. There were decreases with age from the earliest age measured, with an increase in the rate of decline at the age 40–50 years which persists at least to age 80. The mean BMD and corresponding values for Caucasian US/North European populations at femoral neck and AP lumbar spine are shown in Tables 3 and 4. The relation between BMD at the various sites and age variations were analysed by cubic regression models. Figure 1 presents the fitting curves and distribution of age-related changes of BMD at different skeletal sites. Estimates of the prevalence of osteoporosis at the AP lumbar spine and femoral neck in women within age groups were obtained according to the WHO criteria. These results are shown in Tables 5 and 6. The prevalence of osteoporosis and osteopenia at each site were obtained. The prevalence of osteoporosis and osteopenia at the AP lumbar spine in the age groups 51–55, 56–60, 61–65, 66–70, > 70 years were, 7.9%, 19.6%, 26%, 32.1%, 31.8%, and 28.9%, 36.5%, 38.4%, 41.1%, 45.5%, respectively. The prevalence of osteoporosis and osteopenia at the femoral neck in the same age groups were 2.6%, 2%, 12.3%, 14.3%, 22.7% and 28.3%, 39.9%, 43.8%, 50%, 68.2%, respectively.

Table 1.  Distribution of number, height, weight and body mass index (BMI) in different age groups
Age (years)nHeight (cm)Weight (kg)BMI (kg/m2)
  1. Values are mean ± SD.

20–29266158.8 ± 5.860.7 ± 11.724.0 ± 4.4
30–39225158.1 ± 5.764.4 ± 10.825.7 ± 4.3
40–49132158.04 ± 5.368.1 ± 9.427.3 ± 3.7
50–59321156.5 ± 5.369.2 ± 9.228.2 ± 3.8
60–69146154.8 ± 5.568.8 ± 10.828.7 ± 4.3
≥ 70 28154.9 ± 4.767.0 ± 7.627.8 ± 2.7
Table 2.  Bone mineral density (BMD) reference values (gr/cm2) with standard deviation at all sites in Isfahani women
Age (years)nBMD FNBMD total hipBMD L1BMD L2BMD L3BMD L4BMD AP
  1. Values are mean ± SD.

  2. FN = femoral neck; AP = anteroposterior lumbar spine (L2–L4).

20–292660.951 ± 0.1121.004 ± 0.1181.086 ± 0.1261.178 ± 0.1301.225 ± 0.1251.189 ± 0.1291.198 ± 0.120
30–392250.922 ± 0.1160.988 ± 0.1251.092 ± 0.1331.177 ± 0.1361.227 ± 0.1331.192 ± 0.1351.198 ± 0.125
40–491320.910 ± 0.1260.999 ± 0.1321.055 ± 0.1491.139 ± 0.1641.179 ± 0.1531.165 ± 0.1731.162 ± 0.152
50–59 3210.880 ± 0.1200.983 ± 0.1240.987 ± 0.1511.067 ± 0.1691.117 ± 0.1691.113 ± 0.1861.100 ± 0.166
60–691460.796 ± 0.1370.888 ± 0.1450.887 ± 1670.960 ± 0.1831.016 ± 0.1941.004 ± 0.2010.998 ± 0.185
≥ 70 280.711 ± 0.1170.781 ± 0.1150.824 ± 0.1280.888 ± 0.1320.929 ± 0.1760.972 ± 0.1760.934 ± 0.155
Table 3.  Age-related bone mineral desnity (BMD) (g/cm2) at femoral neck in Isfahani and Caucasian women
Age group (years)Isfahani BMDCaucasian BMDP-value
  1. Values are mean ± SD.

20–290.951 ± 0.1120.976P < 0.007
30–390.922 ± 0.1160.970P < 0.000
40–490.913 ± 0.1250.954P < 0.001
50–590.880 ± 0.1200.897P > 0.160
60–690.796 ± 0.1370.832P < 0.004
≥ 700.711 ± 0.1170.783P < 0.005
Table 4.  Age-related bone mineral desnity (BMD) (g/cm2) at AP lumbar spine in Isfahani and Caucasian women
Age group (years)Isfahani BMDCaucasian BMDP-value
  1. Values are mean ± SD.

20–291.198 ± 0.1201.182P < 0.000
30–391.198 ± 0.1251.196P < 0.000
40–491.164 ± 0.1521.201P < 0.009
50–591.100 ± 0.1661.116P > 0.93
60–690.998 ± 0.1851.018P > 0.45
≥ 700.934 ± 0.1550.971P > 0.23
image

Figure 1. Scatter plots and cubic regression curves of age-related changes in bone mineral density (BMD) at different sites in Isfahani women.

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Table 5.  The prevalence of osteoporosis at the femoral neck as defined by WHO criteria, adjusted to the Isfahani population, in women within age groups calculated using peak bone mass (PBM) shown in Table 2 as reference standard
Age groupnOsteoporosis (%)Osteopenia (%)Normal (%)
20–251690 (0%)22 (13%)147 (87%)
26–301280 (0%)21 (16.4%)107 (83.6%)
31–351800 (0%)37 (20.6%)143 (79.4%)
36–40 150 (0%) 2 (13.3%) 13 (86.7%)
41–45 521 (1.9%)13 (25%) 38 (73.1%)
46–501230 (0%)31 (25.2%) 92 (74.8%)
51–551524 (2.6%)43 (28.3%)105 (69.1%)
56–601483 (2%)59 (39.9%) 86 (58.1%)
61–65 739 (12.3%)32 (43.8%) 32 (43.8%)
66–70 568 (14.3%)28 (50%) 20 (35.7%)
≥ 70 225 (22.7%)15 (68.2%)  2 (9.1%)
Table 6.  The prevalence of osteoporosis at the AP lumbar spine (L2 – L4) as defined by the WHO criteria, adjusted to the Isfahani population, in women within age group calculated using Peak Bone Mass (PBM) shown in Table 2 as reference standard
Age groupnOsteoporosis (%)Osteopenia (%)Normal (%)
20–25169 1 (6%)21 (12.4%)147 (87%)
26–30128 0 (0%)21 (16.4%)107 (83.6%)
31–35180 2 (1.1%)27 (15%)151 (83.9%)
36–40 15 0 (0%) 2 (13.3) 13 (86.7)
41–45 52 1 (1.9%)14 (26.9%) 37 (71.2%)
46–50123 7 (5.7%)30 (24.4%) 86 (69.9%)
51–5515212 (7.9%)44 (28.9%) 96 (63.2%)
56–6014829 (19.6%)54 (36.5%) 65 (43.9%)
61–65 7319 (26%)28 (38.4%) 26 (35.6%)
66–70 5618 (32.1%)23 (41.1%) 15 (26.8%)
≥ 70 22 7 (31.8%)10 (45.5%)  5 (22.7%)

Overall the prevalence of osteoporosis at the lumbar spine and femoral neck in women aged ≥ 50 years were 18.8% and 0.06%, respectively, whereas the prevalence of osteopenia at the AP lumbar spine and femoral neck in women aged ≥ 50 years were 35.2% and 37%, respectively. The prevalence of osteopenia and osteoporosis in lumbar spine and femoral neck in women > 50 years old within age group are shown in Figures 2 and 3.

image

Figure 2. The prevalence of osteopenia and osteoporosis at AP lumbar spine as defined by Who criteria, in Isfahani women aged > 50 years calculated using peak bone mass (PBM).

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image

Figure 3. The prevalence of osteopenia and osteoporosis at femoral neck as defined by Who criteria, in Isfahani women aged > 50 years calculated using peak bone mass (PBM).

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DISCUSSION

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES

We conducted our data analysis with eight different regression models and found that the largest coefficients of determination (R2) and best fitting curves were cubic BMD at AP lumbar spine and femoral neck with age-related changes in Isfahani women.

Our cross-sectional BMD analysis of this population showed that peak BMD occurred at age 20–29 years at the FN, total hip and AP lumbar spine.

Age-related BMD at the FN and AP lumbar spine between Isfahani and Caucasian women are summarized in Tables 3 and 4.

As shown in Table 3 there were significant differences between two groups at FN in age-groups 20–29, 30–39, 60–69 and ≥ 70. But there were no significant difference in age-group 50–59.

There were significant differences between two groups at AP lumbar spine in age groups 20–29, 30–39, 40–49. However, there were no significant difference in age group 50–59, 60–69, and ≥ 70. This data suggest that PBM in Isfahani women is less than Caucasians women.

There are some clues that when BMD decreases the risk of fracture increases,10–13 and this appears to be the single best, generally available, objective measure of fracture risk. Encouraged by published guidelines,8 including those of the Osteoporosis Society of Canada,9 it has become common practice to use the WHO criteria to aid in the diagnosis of osteoporosis, osteopenia and fracture risk. The validity of this practice is largely dependent upon the appropriateness and accuracy, with respect to the population in question, of the DXA standard used to determine T-scores. There is evidence that suggests that the best DXA reference standard (PBM) is one derived from the population being assessed. Manufacturer-provided reference ranges often lead to very different estimates of the prevalence of osteoporosis than those calculated from local reference populations.14 Because of heterogeneity in genetic determinants, differences in sunlight exposure geographically, and variations in dietary habits, height or weight, BMD accrual is different among races. Hence it is essential to establish reference values for bone mineral density for every race and country. Population-specific DXA standards have been established in Australia,15,16 Finland,17 United Kingdom,18 United States16,19 and Sweden.20 In each case the results are sufficiently different from each other as to result in substantial differences in T-scores and therefore in estimates of osteoporosis and osteopenia prevalence. In this study, we assessed BMD by DXA in women between 20 and 80 years; BMD of the AP lumbar spine and femoral neck were nearly constant between 20 and 50 years and then declined in both sites. The prevalence of osteopenia at the lumbar spine and femoral neck in women 50 years and older were 35.2% and 37%, respectively. Whereas the prevalence of osteoporosis at the lumbar spine and femoral neck in women 50 years and older were 18.8% and 0.06%, respectively.

In the study that was performed in Tehran by Jamshidian et al. the prevalence of osteopenia at the lumbar spine and femoral neck in women between 40 and 60 years were 34.8% and 26.7%, respectively, whereas the prevalence of osteoporosis at the lumbar spine and femoral neck in women between 40 and 60 years were 15.8% and 2.9%, respectively.21

Guzman Ibara et al. studied 202 postmenopausal women aged 37–74 years, in Medical Centre ‘La Raza’ in December 2001 to June 2002. They calculated the prevalence of osteopenia and osteoporosis in normal postmenopausal women at lumbar spine and femoral neck (43.5%, 19.8%–48%, 7.4%), respectively.22

In a study by Diaz et al. in a Spanish female population, the prevalence of osteoporosis in women older than 50 years at the lumbar spine and femoral neck were 22.8% and 9.1%, respectively.23

Looker et al. estimated the prevalence of osteoporosis at the femoral neck in US non-Hispanic White women > 50 years using NHANES III reference standards and found a rate of 18%.19 Using the CaMos standard the prevalence of osteoporosis in Canadian women aged > 50 years was 7.93% whereas when the NHANES standard is used in the same population the prevalence is found to be 22%. The prevalence of osteoporosis at the femoral neck as defined by WHO criteria, in Isfahani women 50 years and older was 10.78%. There are some factors that might contribute to this difference between the prevalence of osteoporosis in different populations: PBM, age distribution, time of age-dependent bone loss and the rate of bone loss.

In summary, in our results the prevalence of osteopenia and osteoporosis are different from other populations, therefore an Isfahani reference BMD for women has been established for the lumbar spine and femoral neck.

REFERENCES

  1. Top of page
  2. Abstract
  3. INTRODUCTION
  4. SUBJECTS AND METHODS
  5. RESULTS
  6. DISCUSSION
  7. REFERENCES
  • 1
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