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Decreased bone mineral density associated with early menopause progresses for at least ten years: Cross-sectional comparisons between early and normal menopausal women
Bone Vol. 18, No. 3 March 1996~227-231
ELSEVIER
Decreased Bone Mineral Density Associated with Early Menopause Progresses for at Least Ten Years: Cross-sectional Comparisons Between Early and Normal Menopausal Women H. OHTA, I. SUGIMOTO, A. MASUDA, F. HORIGUCHI, and S. NOZAWA
S. KOMUKAI,
Y. SUDA, K. MAIUTA,
K. TAKAMATSU,
Department of Obstetrics and Gynecology, School of Medicine, Keio University, Tokyo, Japan
To establish whether early onset of menopause carries an increased risk of osteoporosis, we compared the bone mineral density (BMD) of the second to fourth lumbar vertebrae (L24) between 18 women who had menopause before 43 years of age (early menopause group) and 19 women who had menopause after reaching 43 years of age (normal menopause group). Serum levels of calcium, phosphorus, calcitonin, intact parathyroid hormone, luteinixing hormone (LID, follicle-stimulating hormone (FSH), estradiol (E,), and alkaline phosphatase activity were measured, and urine samples were analyzed to derive calcium/creatinine, hydroxyprolinel creatinine, pyridinoline/creatinine, and deoxypyridinoline/ creatinine (D-Pyr/Cr) ratios. Mean BMD was significantly lower in the early menopause group than in the normal menopause group, and individual BMD values in about half of the subjects in the former group were below the fracture threshold for Japanese women. Serum concentrations of LH, FSH, and E, were slightly, but not significantly, lower in the early menopause group than in the normal menopause group. The D-Pyr/Cr ratio was significantly higher in the early menopause group than in the normal menopause group. There was no correlation between L2-4 BMD and age or the number of years ,after menopause in the normal menopause group, but both age and the number of years after menopause were negatively correlated with L2-4 BMD in the early menopause group. These results indicate that BMD in women who have early menopause continues to decline for up to 10 years, and that menopause and aging increase the risk of osteoporosis. (Bone 18:227-231; 1996)
in the genesis of osteoporosis, the influence of early menopause on bone metabolism has not yet been quantitatively assessed. The reasons for this are twofold: (1) compared with the number of women who undergo OPX, fewer women have early menopause; (2) early menopause has only recently been recognized to be a useful model by which to study osteoporosis in women. Although some reports indicate no premenopausal decrease in BMD,9,** studies in Japan have shown that the reduction in BMD that accompanies hypoestrogenism due to menopause or other factors differs between cancellous bone and cortical bone, with the former showing a more remarkable decrease.‘7,23 The BMD of cancellous bone starts to decrease before menopause,25 and this decrease is accelerated by the hypoestrogenism caused by menopause,3,7.14.1723 Accelerated loss of BMD persists generally for 5 to 10 years after menopause. The period 3 to 4 years after menopause is characterized by a decrease in the number of trabeculae of over 3% per year.27 About 10 years after menopause, the annual decrease in BMD drops to about l%, with mainly cortical bone being affected. We thus have achieved a fairly good understanding of the factors that precipitate osteoporosis in women who have menopause at a normal age. Whether or not early menopause imposes an increased risk of osteoporosis, however, is still an open question. Some investigators claim that early menopause increases the risk of osteoporosis,‘3 while others reject this theory.3’ The present study was designed to determine whether there are differences in BMD between women who have early menopause and women who have menopause at a normal age, and to investigate potential differences in sex steroids and bone metabolism between these two groups of subjects.
Key Words: Biochemical marker; Bone mineral density; Deoxypyridinoline; Early menopause; Osteoporosis; Risk factor.
Materials and Methods Materials
Introduction This study included a total of 37 women who underwent routine voluntary health checkups for involutional diseases due to estrogen deficiency at the outpatient clinic of our department between April 1991 and December 1992. They had similar levels of physical activity and dietary characteristics. Eighteen of the subjects (age: 46.8 + 1.5 years, mean + SE) had early menopause, defined as menopause before 43 years of age, and 19 (age: 49.5 + 0.6 years) had normal menopause, defined as menopause be-
Although early menopause, like oophorectomy (OPX), provides a model suitable for studying the role played by hypoestrogenism
Address for correspondence and reprints: Hiroaki Ohta, M.D., Department of Obstetrics and Gynecology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160, Japan.
0 1996 by Elsevier Science Inc. All rights reserved.
221 SD1
8756.3282/96/$15.00 8756-3282(95)00480-7
228
H. Ohta et al. Progressive loss of BMD after early menopause
Bone Vol. 18, No. 3 March 1996:227-23 1
Table 1. Subjects
Early menopause group (n = 18) Normal menopause group (n = 19)
Age (years)
Height
Body weight
Body mass
Age at menopause (years)
Interval after menopause (months)
(m)
(kg)
index
[Mean & SE (range)]
[Mean f SE (range)]
46.8 f 1.5 (33-56) 49.5 f 0.6 (44-53)
1.54 f 0.02 (1.42-1.63) 1.55 f 0.01 (1.48-1.65)
49.8 + 1.7 (40.0-58.0) 49.0 + 0.8 (43.G53.5)
21.OeO.6 (17.4-24.7) 20.4 k 0.4 (16.624.2)
36.9 2 1.1” (27.42) 47.0 f 0.5” (4451)
116.0 + 20.4a (14-353) 34.7 + 5.0” (12-80)
=p < 0.001 tween the ages of 43 and 55 years (Table 1). The two groups were matched for age and body size based on BW, BH, and BMI. The 18 subjects in the early menopause group had menopause 14 to 353 months before entry into the study (mean + SE: 116.0 f 20.4 months). The 19 subjects in the normal menopause group had menopause 12 to 80 months prior to entry (mean f SE: 34.7 + 5.0 months) (Table 1). None of the subjects had any conditions (other than menopause) nor were receiving any drugs that might influence bone or calcium metabolism. In addition, none of the subjects had bone fractures. Methods Measurement of BMD. BMD was measured using a Dual X-ray Bone Densitometer XR-26 (Norland Corp., Ft. Atkinson, WI, USA). BMD from the second to fourth lumbar vertebrae (L2-4) was measured by AP dual X-ray absorptiometry (DXA) as reported previously,26 and the mean value (L2-4 BMD) was calculated and recorded. At our institute, the coefficient of variance (CV) of L2-4 BMD was 1.27% for the short-term precision (in vivo) of this technique, and 0.122% for the long-term precision (in vitro). Laboratory examinations. The following laboratory examinations were performed for all subjects at the times of BMD assay. Serum levels of calcium (Ca), phosphorus (P), alkaline phosphatase (Al-P) activity, calcitonin (CTN), intact paratbyroid hormone (PTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol (E2) were determined as described previously.18-23,26 Urine samples were spot samples and were analyzed to derive the Ca/creatinine (Cr) ratio, hydroxyproline (Hpr)/Cr ratio, pyridinoline (Pyr)/Cr ratio, and deoxypyridinoline (D-Pyr)/Cr ratio as reported previously. 1S-23.26 Statistical analysis. The results are presented as means f SE. Student’s t-test was used for statistical analysis of data, and p values of 0.05 or less were considered to indicate statistical significance. Results
tween the groups was not significant (Table 2). There were no significant differences between the groups in serum P or serum Ca levels (Table 2). The CTN level was higher in the early menopause group than in the normal menopause group, but the difference was not significant (Table 2). The intact PTH was lower in the early menopause group than in the normal menopause group, but there was no significant difference between the groups (Table 2). The urinary (u) Ca/Cr ratio, which can reflect bone resorption to some extent, was higher in the early menopause group, but the difference from the normal menopause group was not significant (Table 2). The bone resorption marker U-HprlCr did not differ appreciably between the two groups, and there was no significant difference (Table 2). The new bone resorption marker, PyrKr ratio, representing pyridinium crosslinks, was 35.94 + 4.85 nmol/mmol Cr in the early menopause group compared with 28.3 2 5.15 nmol/mmol in the normal menopause group. Although the value was higher in the early menopause group, there was no significant difference from the normal menopause group (Figure 2). U-D-Pry/Cr was 18.52 + 3.69 nmol/mmol Cr in the early menopause group compared with 6.02 + 2.3 1 nmol/mmol Cr in the normal menopause group. This difference was significant @ < 0.05, t = 2.869) (Figure 2). Serum levels of the gonadotropins LH and FSH were higher in the normal menopause group than in the early menopause group, but the differences were not significant (Table 2). Serum E2 level was 13.9 f 1.6 pg/mL in the early menopause
g/cm2
jfSE 1 .oo 0.90
Bone Mineral Density 0.80 BMD of L2-4 in the early menopause group (0.81 + 0.05 g/cm’) was significantly lower than in the normal menopause group (1.00 f 0.04 g/cm’) (p < 0.01, t = 3.118) (Figure 1).
0.70
Biochemistry Al-P activity in the early menopause group and the normal menopause group was 202.7 * 19.5 IU and 182.6 f 10.6 IU, respectively. Although the value was higher in the early menopause group than in the normal menopause group, the difference be-
Normal menopause group (n=l9)
Early menopause group (n-1 8)
Figure 1. L2-4 BMD measured by DXA.
H. Ohta et al. Progressive loss of BMD after early menopause
Bone Vol. 18, No. 3 March 1996:227-23 1 Table 2. Serum and urinary biochemical data. These data were not significant differences in the two groups
Alkaline phosphatase (IU) S-Ca (mg/dl) S-P (mg/dl) Calcitonin (pg/mL) intact PTH (pg/mL) U-C&r U-HydroxyprolineKr LH (mIU/mL) FSH (mIU/mL) Estradiol (pg/mL)
Early menopausal group (n = 18) (mean + SE)
Normal menopausal group (n = 19) (mean f SE)
202.7 -+ 19.5 9.4 + 0.1 3.4 + 0.1 28.3 * 3.0 29.4 ” 2.6 0.22 f 0.03 0.01 f 0.001 29.1 + 4.6 71.1 * 9.0 13.9 + 1.6
182.6 i 10.6 9.2 + 0.1 3.4 f 0.1 23.6 * 2.1 33.8 f 2.6 0.19 f 0.02 0.01 + 0.001 38.8 + 3.6 83.8? 8.4 17.4 f 3.2
group and 17.4 f 3.2 pg/mL in the normal menopause group. Although the value was lower in the former group, the difference was not significant (Table 2).
Discussion Age-related changes i.n axial bone differ from those in peripheral bone. The former shows a relatively early decrease in BMD after attainment of peak bone mass.2,8 With aging there is an overall decrease in BMD,‘0,15,29 which is accelerated by menopaUse.7.sJ4.23 As reported previously, menopause has diverse effects on the dynamics of bone metabolism.23 Although signiticant postmenopausal increases in Al-P and osteocalcin activity suggest enhanced bone formation potential, the significant rise in U-Hpr/Cr ratio that occurs after menopause indicates increased bone resorption. BMD decreases when the amount of bone resorption surpasses that of bone formation. The main factor implicated in the postmenopausal drop in BMD is a failure to suppress bone resorption caused by decreased serum levels of not only E2 but also e&one (E,). 23 This consequently leads to elevated serum Ca levels, an associated inhibition of paratbyroid hormone function, and suppression of vitamin D activation in the kidney. After menopause, osteoporosis is thought to progress with aging.30 Seeman et al.31 reported that the pathogenesis of osteoporosis after early menopause was similar to that after normal menopause. They found that tbe decrease in BMD was initially greater in women with early menopause than in premenopausal women matched for age, but that the difference between these groups became indistinct after about 10 years. Although still unproven, this theory is widely accepted. The present study, however, demonstrated that L2-4 BMD was significantly lower in the early menopause group, in which about 10 years had passed since menopause, than in the normal menopause group, about 3 years after menopause, although the groups were matched for age and body size. In addition, the mean L2-4 BMD in the 18 subjects in the early menopause group was 0.81 rf:0.65 g/cm2, which was higher than the 90th percentile value for bone fractures (0.770 g/cm2) determined by XR-26, also used in the present study, by the Silver Science Study Group of the Japanese Ministry of Health and Welfare.33 However, individual patient analysis revealed that 10 (55.6%) of the 18 patients in the early menopause group had a L2-4 BMD below the threshold value of 0.770 g/cm2, indicating a high risk of fracture. In contrast, L2~l
229
BMD was below the fracture threshold in only 1 of the 19 patients (5.3%) in the normal menopause group. Subjects who have early menopause, therefore, have an increased risk of developing osteoporosis, as indicated by the absolute value of their L2-4 BMD and the fact that this value exceeded the 90th percentile of the bone fracture threshold. The factors responsible for the low BMD in the early menopause group are unknown and their clarification must await future studies. L24 BMD was lower in the early menopause group than in the normal menopause group, despite lack of a significant difference between the groups in age or body size. Serum levels of E2 and gonadotropins such as LH and FSH were slightly, but not significantly, lower in the early menopause group than in the normal menopause group. The mean D-Pyr/Cr ratio, serving as a bone metabolic marker (D-Pyr is the only deoxy metabolite of pyridinoline), was over threefold higher in the early menopause group than in the normal menopause group. However, although the mean PyrKr ratio was about 27% higher in the early menopause group than in the normal menopause group, the difference between the groups was not significant. In association with the metabolism of bone tissue, i.e., bone resorption, these pyridinolines are excreted in the urine as collagen crosslinks, formed by the breakdown of collagen. Pyridinoline is reported to be derived from bone and cartilage tissue, while its deoxy metabolite, DPyr, is derived from bone tissue.5,6,32 These markers are clinically useful for monitoring the status of bone metabolic diseases, bone metastasis, and endocrinological diseases, as well as assessing the response of these conditions to therapy, but they have recently attracted interest as bone resorption markers that rise remarkably after OPX or in postmenopausal osteoporosis.4*32 A recent report by the authors26 documents studies in which the mean Pyr/Cr ratio in patients undergoing OPX was 30% higher than that in premenopausal control subjects matched for age and body size. In OPX subjects, D-Pyr/Cr ratio did not change significantly compared with control subjects,26 but in postmenopausal patients with osteoporosis, both PyrKr ratio and D-PyrKr ratio were twofold higher than contro1.4*32 Although these were studies in menopausal patients with established osteoporosis, PyrKr ratio has been found to increase by 60% and D-Pyr/Cr by 82% in normal menopausal subjects.34 Hassager et al.’ ’reported a 30%-50% increase in PyrKr ratio 6 months after menopause compared with before menopause. Whether the Pyr/ Cr ratio or the D-PyrKr ratio is more useful as a clinical marker
U-PyridinolineKr nmoVmmol Cr
U-DeoxypyridinolineKr nmoVmmol Cr XrtSE
45
1
40
1
T
35 15 30 10
25
(n-19)
(n-1 8)
(n-19)
(n-1 8)
Figure 2. Urinary markers of bone absorption.
230
H. Ohta et al. Progressive loss of BMD after early menopause
Bone Vol. 18, No. 3 March 1996:227-231
g/cm’
n=19
n=19
1.50
r=O.3193 1.25
Y=o.180+ NS
.
P s . r; .A
.
l.OO-
.
.
??
.
.
??
.
1 .oo
?? . ??
.
??*
:
.
.
.
.
8
??
0.75
yrs
50
0.50
5.071 X
.
.
0.50’ 40
Y=O.996NS
??
.
.
.
-
1.25
;
. 0.75
r=-0.0775 1.606X
? ?
? ?
mon
r
0
24
48
72
96
120
interval after menopause
Figure 3. Relationship
between L24
BMD and age and interval after menopause
is currently unclear, but these values may differ somewhat depending on when urine samples were obtained, the assay method used, and the types of patients studied. Unlike conventional bone metabolic markers, these pyridinolines are regarded by the authors to be able to forecast the risk of a drop in L2-4 BMD in the forthcoming 6 months.24 Although D-Pyr/Cr ratio has been reported to be 11.97 f 2.68 mmoVnmo1 Cr (mean ? SE) in OPX subjects (n = 90),26 the value was abnormally high (18.52 + 3.69 mmol/nmol Cr) in the early menopause group in the present study. The significantly higher value than in the normal menopause group foretells of a further decline in BMD in the future. While menopause-related BMD changes continue up to 10 years after the event, the greatest changes occur in the first or second year; therefore, the fact that an average period since menopause in the normal group was approximately 3 years (mean 34 months) is of importance in this comparative study. As illustrated in Figures 3 and 4, although L24 BMD did not correlate with either age or time after menopause in the normal menopause group, L2-4 BMD in the early menopause group decreased with increasing age (r = -0.7043, p < 0.01) and with the number of years after menopause (r = -0.6107, p < 0.01). Future decreases in BMD, associated with
g/cm2
n=18
1.501]
1.25
0.50-1 30
k-O.7043 Y=l.690p
.
in the normal menopause
group.
increasing age and number of years after menopause, are therefore highly likely in women who have early menopause. There are slight country-specific differences in the criteria defining the cutoff age for early menopause. In the United Kingdom16 and the United Statesi early menopause is defined as menopause at age 40 or before, whereas the cutoff point is 42 years in Japan and 45 years in Argentina.’ Various experimental and clinical studies have addressed potential causes for premature onset of menopause. Autoimmune disease has been implicated as one possible cause, but evidence supporting this or other hypotheses is currently lacking. However, since at least 1%-2% to less than 5% of all women are estimated to have early menopause, the number of patients is considerable. Furthermore, as demonstrated in this study, women with early menopause have lower BMD than those with normal menopause, and about half of the former group have a BMD below the fracture threshold. In addition, the D-Pyr ratio and the negative correlation between BMD and age and the number of years after menopause in the early menopause group indicates a high risk of a future decrease in BMD. Considering the remarkable prolongation of mean life expectancy for women to about 82 years in Japan, an increased incidence of osteoporosis seems inevitable.
n=lf
1.501 r=-0.6107 Y=O.986p-Co.01
1.881X 1.25-
.
1.368X
mon
40
50
age Figure 4. Relationship
between L24
60
0
60
120
180
240
300
360
interval after menopause BMD and age and interval after menopause
in the early menopausal
group.
Bone Vol. 18, No. 3 March 1996:227-231
Acknowledgments:
This work was supported in part by the Ministry of Education of Japan (Grant No. 06671684), and its content was presented at the 1 lth congress of the Japan Society for Bone and Mineral Research in Yokohama, Japan, July 31-August 2, 1993. We express our gratitude to Professor J. Patrick Barron, Tokyo Medical College, for reviewing the manuscript.
References 1. Bagur, A. C. and Mautalen, C. A. Risk for developing osteoporosis in untreated premature menopause. Calcif Tissue Int 51:&7; 1992. 2. Buchanan, J. R., Myers, C., Lloyd, T., and Green R. B., III. Early vertebral trabecular bone loss in normal premenopausal women. J Bone Miner Res 3:583-587; 1988. 3. Cann, C. E., Genant, H. K., Kolb, F. O., and Ettinger, B. Quantitative computed tomography for prediction of vertebral fracture risk. Bone 6: 1-7; 1985. 4. Delmas, P. D., Schletnmer, A., Gineyts, E., Riis, B., and Christiansen, C. Urinary excretion of pyridinoline crosslinks correlates with bone turnover tneawed on iliac crest biopsy in patients with vertebral osteoporosis. J Bone Miner Res 6639-644; 1991. 5. Eyre, D. Collagen cross-linking amino acids, Methods Enzymol 144: 115-139; 1987. 6. Fujimoto, D., Motiguchi, T., Ishida, T., and Hayashi, H. The structure of pyridinoline, a collagen crosslink. Biochem Biophys Res Commun 84:52-57; 1978. 7. Gallagher, J. C., Goldgar, D., and Moy, A. Total bone calcium in normal women: effect of age and menopause status. J Bone Miner Res 2:491496; 1987. 8. Geusens, P., Dequeker, I., Verstraeten, A., and Nijs, J. Age-, sex- and tnenopause-related changes of vertebral and peripheral bone: population study using dual and single photon absorptiometry and radiogrammetry. J Nucl Med 27:154&1549; 1986. 9. Hansen, M. A. Assessment of age and risk factors on bone density and bone turnover in healthy premenopausal women. Osteoporosis Int 4:123-128; 1994. 10. Hansson, T. and Roos, B. Age changes in the bone mineral of the lumbar spine in normal women. Calcif Tissue Int 38:249-251; 1986. 11. Hassager, C., Colwell, A., Assiri, A.M. A., Eastell, R., Russell, R. G. G., and Christiansen, C. Effect of menopause and hormone replacement therapy on urinary excretion of pyridinium cross-links: a longitudinal and cross-sectional study. Clin Endoctinol 37:45-50; 1992. 12. Johnson. B. E., Lucasey, B., Robinson, R. G., and Luke& B. P. Contributing diagnoses in osteoporosis. The value of a complete medical evaluation. Arch Intern Med 149:1069-1072; 1989. 13. Jones, K. P., Ravnikar, V. A., Tulchinsky, D., and Schiff, I. Comparison of bone density in amenorrheic women due to athletics, weight loss, and pretnature menopause. Obstet Gynecol 66:5-8; 1985. 14. Krolner, B. and Pars Nielsen, S. Bone mineral content of the lumbar spine in normal and osteoporotic women: cross-sectional and longitudinal studies. Clin Sci 621329-336; 1982. 15. Matkovic, V., Jelic, T., Wardlaw, G. M., Ihch, J. Z., Gael, P. K., Wright, J. K., Andon, M. B., Smith, K. T., and Heaney, R. P. Timing of peak bone mass in Caucasian females and its implication for the prevention of osteoporosis. I Clin Invest 93:799-808; 1994. 16. Mitchell, A. Too young for the change? Menopause in women under 40. Prof Nurse 5:11&112; 1989. 17. Ohta, H., Nemoto, K., Nozawa, S., and Iizuka, R. Changes in bone mineral content and bone metabolism related to menopause. Acta Obstet Gynaec Jpn 41:1447-1454; 1989 (in Japanese, with English abstract). 18. Ohta, H., Nemoto, K., Nozawa, S., and Iizuka, R. Mechanism of the decrease in metacarpal bone mineral content due to oopherectomy. Acta Obst Gynaec Jpn 41:333-340; 1989 [in Japanese, with English abstract). 19. Ohta, H., Nemoto, K., Nozawa, S., and Iizuka, R. Assessment of osteopenia
Progressive
H. Ohta et al. loss of BMD after early menopause
231
following oophorectomy by quantitative computed tomography and its relation with Ca-regulating hormones. Acta Obstet Gynaec Jpn 41:1471-1478; 1989 (in Japanese, with English abstract). 20. Ohta, H., Nemoto, K., Nozawa, S., and Iizuka, R. Bone mineral loss due to premenopausal oophorectomy assessed by dual photon absorptiometry Acta Obstet Gynaec Jpn 42: 185-191; 1990 (in Japanese, with English abstract). 21. Ohta, H., Makita, K., Suds, Y., Ikeda, T., Masurawa, T., and Nozawa, S. Influence of oophorectomy on semm levels of sex steroids and bone metabolism and assessment of bone mineral density in lumbar trabecular bone by QCT-C value. J Bone Miner Res 7:659-665; 1992. 22. Ohta, H., Masuzawa, T., Ikeda, T., Suds, Y., Makita, K., and Nozawa, S. Which is more osteoporosis-inducing, tnenopause or oophorectomy? Bone Miner 19:273-285; 1992. 23. Ohta, H., Ikeda, T., Masuzawa, T., Makita, K., Suda, Y., and Nozawa, S. Differences in axial bone mineral density, sewn levels of sex steroids, and bone metabolism between postmenopausal and age- and body size-matched premenopausal subjects. Bone 14: 11l-l 16; 1993. 24. Ohta, H., Kotnukai, S., Ikeda, T., Masuzawa, T., Suds, Y., Makita, K., Horiguchi, F., and Nozawa, S. Early diagnosis of osteoporosis and indication of treatment in oophorectomized subjects. J Jpn Menopause Sot 1:202-210; 1993 (in Japanese, with English abstract). 25. Ohta, H. Sex steroid hormones and osteoporosis. Clin Physician 20:1680-1684; 1994 (in Japanese). 26. Ohta, H., Makita, K., Suds, Y., Masuzawa, T., Ikeda, T., Komukai, S., Masuda, A., Yoshimura, Y., Taketomi, S., and Nozawa, S. Urinary levels of pyridinium crosslinks of collagen and lumbar bone mineral density measured by DXA after oophorectomy. J Jpn Menopause Sot 2:201-209; 1994. 27. Part%, A. M. Trabecular bone architecture in the pathogenesis and prevention of fracture. Am J Med 82:68-72; 1987. 28. Raw, P., Hetland, M. L., Overgaatd, K., and Christiansen, C. Premenopausal and postmenopausal changes in bone mineral density of the proximal femur measured by dual-energy X-ray absorptiometry. J Bone Miner Res 9:19751980; 1994. 29. Riggs. B. L., Wahner, H. W., Melton, L. J., III, Richelson, L. S., Judd, H. L., and Offord, K. P. Rates of bone loss in the appendicular and axial skeletons of women. Evidence of substantial vertebral bone loss before menopause. J Clin Invest 77:1487-1491; 1986. 30. Riggs, B. L. and Melton, L. J., III. Medical progress: Involutional osteoporosis. N Engl J Med 314:1676-1686; 1986. 31. Seeman, E., Cooper, M. E., Hopper, I. L., Parkinson, E., McKay, J., and Jerums, G. Effect of early menopause on bone mass in normal women and patients with osteoporosis. Am J Med 85:213-216; 1988. 32. Seibel, M. J., Ratcliffe, A., Cosman, F., Shea, V., Henington, B., Dempster, D., and Lindsay, R. Urinary hydroxy-pytidinium crosslinks of collagen are markers of bone resorption and estrogen efficacy in postmenopausal osteoporosis. Tram Orthop Res Sot 16:S279; 1991. Shiraki, M., Kaneda, S., Nakamura, T., Nakamura, T., Kurokawa, T., Inoue, T., Totnita, A., Morii, H., Fujita, T., Fukase, M., Tsutsuizumi, M., Fukunaga, H., Yamamoto, K., Notimatsu, T., Morita, R., and Orimo, H. Age-related changes in bone mineral density and the fracture threshold. J Bone Miner Met 8:S283; 1990 (in Japanese). Uebelhatt, D., Schlemmer, A., Johansen, J. S., Gineyts, E., Christiansen, C., and Delmas, P. D. Effect of menopause and hormone replacement therapy on the urinary excretion of pytidinium cross-links. J Clin Endocrinol Metab 72~367-373; 1991.
Dare Received: June 19, 1995 Date Revised: October 25, 1995 Dare Accepted: October 31, 1995
ELSEVIER
Decreased Bone Mineral Density Associated with Early Menopause Progresses for at Least Ten Years: Cross-sectional Comparisons Between Early and Normal Menopausal Women H. OHTA, I. SUGIMOTO, A. MASUDA, F. HORIGUCHI, and S. NOZAWA
S. KOMUKAI,
Y. SUDA, K. MAIUTA,
K. TAKAMATSU,
Department of Obstetrics and Gynecology, School of Medicine, Keio University, Tokyo, Japan
To establish whether early onset of menopause carries an increased risk of osteoporosis, we compared the bone mineral density (BMD) of the second to fourth lumbar vertebrae (L24) between 18 women who had menopause before 43 years of age (early menopause group) and 19 women who had menopause after reaching 43 years of age (normal menopause group). Serum levels of calcium, phosphorus, calcitonin, intact parathyroid hormone, luteinixing hormone (LID, follicle-stimulating hormone (FSH), estradiol (E,), and alkaline phosphatase activity were measured, and urine samples were analyzed to derive calcium/creatinine, hydroxyprolinel creatinine, pyridinoline/creatinine, and deoxypyridinoline/ creatinine (D-Pyr/Cr) ratios. Mean BMD was significantly lower in the early menopause group than in the normal menopause group, and individual BMD values in about half of the subjects in the former group were below the fracture threshold for Japanese women. Serum concentrations of LH, FSH, and E, were slightly, but not significantly, lower in the early menopause group than in the normal menopause group. The D-Pyr/Cr ratio was significantly higher in the early menopause group than in the normal menopause group. There was no correlation between L2-4 BMD and age or the number of years ,after menopause in the normal menopause group, but both age and the number of years after menopause were negatively correlated with L2-4 BMD in the early menopause group. These results indicate that BMD in women who have early menopause continues to decline for up to 10 years, and that menopause and aging increase the risk of osteoporosis. (Bone 18:227-231; 1996)
in the genesis of osteoporosis, the influence of early menopause on bone metabolism has not yet been quantitatively assessed. The reasons for this are twofold: (1) compared with the number of women who undergo OPX, fewer women have early menopause; (2) early menopause has only recently been recognized to be a useful model by which to study osteoporosis in women. Although some reports indicate no premenopausal decrease in BMD,9,** studies in Japan have shown that the reduction in BMD that accompanies hypoestrogenism due to menopause or other factors differs between cancellous bone and cortical bone, with the former showing a more remarkable decrease.‘7,23 The BMD of cancellous bone starts to decrease before menopause,25 and this decrease is accelerated by the hypoestrogenism caused by menopause,3,7.14.1723 Accelerated loss of BMD persists generally for 5 to 10 years after menopause. The period 3 to 4 years after menopause is characterized by a decrease in the number of trabeculae of over 3% per year.27 About 10 years after menopause, the annual decrease in BMD drops to about l%, with mainly cortical bone being affected. We thus have achieved a fairly good understanding of the factors that precipitate osteoporosis in women who have menopause at a normal age. Whether or not early menopause imposes an increased risk of osteoporosis, however, is still an open question. Some investigators claim that early menopause increases the risk of osteoporosis,‘3 while others reject this theory.3’ The present study was designed to determine whether there are differences in BMD between women who have early menopause and women who have menopause at a normal age, and to investigate potential differences in sex steroids and bone metabolism between these two groups of subjects.
Key Words: Biochemical marker; Bone mineral density; Deoxypyridinoline; Early menopause; Osteoporosis; Risk factor.
Materials and Methods Materials
Introduction This study included a total of 37 women who underwent routine voluntary health checkups for involutional diseases due to estrogen deficiency at the outpatient clinic of our department between April 1991 and December 1992. They had similar levels of physical activity and dietary characteristics. Eighteen of the subjects (age: 46.8 + 1.5 years, mean + SE) had early menopause, defined as menopause before 43 years of age, and 19 (age: 49.5 + 0.6 years) had normal menopause, defined as menopause be-
Although early menopause, like oophorectomy (OPX), provides a model suitable for studying the role played by hypoestrogenism
Address for correspondence and reprints: Hiroaki Ohta, M.D., Department of Obstetrics and Gynecology, School of Medicine, Keio University, 35 Shinanomachi, Shinjuku-ku, Tokyo 160, Japan.
0 1996 by Elsevier Science Inc. All rights reserved.
221 SD1
8756.3282/96/$15.00 8756-3282(95)00480-7
228
H. Ohta et al. Progressive loss of BMD after early menopause
Bone Vol. 18, No. 3 March 1996:227-23 1
Table 1. Subjects
Early menopause group (n = 18) Normal menopause group (n = 19)
Age (years)
Height
Body weight
Body mass
Age at menopause (years)
Interval after menopause (months)
(m)
(kg)
index
[Mean & SE (range)]
[Mean f SE (range)]
46.8 f 1.5 (33-56) 49.5 f 0.6 (44-53)
1.54 f 0.02 (1.42-1.63) 1.55 f 0.01 (1.48-1.65)
49.8 + 1.7 (40.0-58.0) 49.0 + 0.8 (43.G53.5)
21.OeO.6 (17.4-24.7) 20.4 k 0.4 (16.624.2)
36.9 2 1.1” (27.42) 47.0 f 0.5” (4451)
116.0 + 20.4a (14-353) 34.7 + 5.0” (12-80)
=p < 0.001 tween the ages of 43 and 55 years (Table 1). The two groups were matched for age and body size based on BW, BH, and BMI. The 18 subjects in the early menopause group had menopause 14 to 353 months before entry into the study (mean + SE: 116.0 f 20.4 months). The 19 subjects in the normal menopause group had menopause 12 to 80 months prior to entry (mean f SE: 34.7 + 5.0 months) (Table 1). None of the subjects had any conditions (other than menopause) nor were receiving any drugs that might influence bone or calcium metabolism. In addition, none of the subjects had bone fractures. Methods Measurement of BMD. BMD was measured using a Dual X-ray Bone Densitometer XR-26 (Norland Corp., Ft. Atkinson, WI, USA). BMD from the second to fourth lumbar vertebrae (L2-4) was measured by AP dual X-ray absorptiometry (DXA) as reported previously,26 and the mean value (L2-4 BMD) was calculated and recorded. At our institute, the coefficient of variance (CV) of L2-4 BMD was 1.27% for the short-term precision (in vivo) of this technique, and 0.122% for the long-term precision (in vitro). Laboratory examinations. The following laboratory examinations were performed for all subjects at the times of BMD assay. Serum levels of calcium (Ca), phosphorus (P), alkaline phosphatase (Al-P) activity, calcitonin (CTN), intact paratbyroid hormone (PTH), luteinizing hormone (LH), follicle-stimulating hormone (FSH), and estradiol (E2) were determined as described previously.18-23,26 Urine samples were spot samples and were analyzed to derive the Ca/creatinine (Cr) ratio, hydroxyproline (Hpr)/Cr ratio, pyridinoline (Pyr)/Cr ratio, and deoxypyridinoline (D-Pyr)/Cr ratio as reported previously. 1S-23.26 Statistical analysis. The results are presented as means f SE. Student’s t-test was used for statistical analysis of data, and p values of 0.05 or less were considered to indicate statistical significance. Results
tween the groups was not significant (Table 2). There were no significant differences between the groups in serum P or serum Ca levels (Table 2). The CTN level was higher in the early menopause group than in the normal menopause group, but the difference was not significant (Table 2). The intact PTH was lower in the early menopause group than in the normal menopause group, but there was no significant difference between the groups (Table 2). The urinary (u) Ca/Cr ratio, which can reflect bone resorption to some extent, was higher in the early menopause group, but the difference from the normal menopause group was not significant (Table 2). The bone resorption marker U-HprlCr did not differ appreciably between the two groups, and there was no significant difference (Table 2). The new bone resorption marker, PyrKr ratio, representing pyridinium crosslinks, was 35.94 + 4.85 nmol/mmol Cr in the early menopause group compared with 28.3 2 5.15 nmol/mmol in the normal menopause group. Although the value was higher in the early menopause group, there was no significant difference from the normal menopause group (Figure 2). U-D-Pry/Cr was 18.52 + 3.69 nmol/mmol Cr in the early menopause group compared with 6.02 + 2.3 1 nmol/mmol Cr in the normal menopause group. This difference was significant @ < 0.05, t = 2.869) (Figure 2). Serum levels of the gonadotropins LH and FSH were higher in the normal menopause group than in the early menopause group, but the differences were not significant (Table 2). Serum E2 level was 13.9 f 1.6 pg/mL in the early menopause
g/cm2
jfSE 1 .oo 0.90
Bone Mineral Density 0.80 BMD of L2-4 in the early menopause group (0.81 + 0.05 g/cm’) was significantly lower than in the normal menopause group (1.00 f 0.04 g/cm’) (p < 0.01, t = 3.118) (Figure 1).
0.70
Biochemistry Al-P activity in the early menopause group and the normal menopause group was 202.7 * 19.5 IU and 182.6 f 10.6 IU, respectively. Although the value was higher in the early menopause group than in the normal menopause group, the difference be-
Normal menopause group (n=l9)
Early menopause group (n-1 8)
Figure 1. L2-4 BMD measured by DXA.
H. Ohta et al. Progressive loss of BMD after early menopause
Bone Vol. 18, No. 3 March 1996:227-23 1 Table 2. Serum and urinary biochemical data. These data were not significant differences in the two groups
Alkaline phosphatase (IU) S-Ca (mg/dl) S-P (mg/dl) Calcitonin (pg/mL) intact PTH (pg/mL) U-C&r U-HydroxyprolineKr LH (mIU/mL) FSH (mIU/mL) Estradiol (pg/mL)
Early menopausal group (n = 18) (mean + SE)
Normal menopausal group (n = 19) (mean f SE)
202.7 -+ 19.5 9.4 + 0.1 3.4 + 0.1 28.3 * 3.0 29.4 ” 2.6 0.22 f 0.03 0.01 f 0.001 29.1 + 4.6 71.1 * 9.0 13.9 + 1.6
182.6 i 10.6 9.2 + 0.1 3.4 f 0.1 23.6 * 2.1 33.8 f 2.6 0.19 f 0.02 0.01 + 0.001 38.8 + 3.6 83.8? 8.4 17.4 f 3.2
group and 17.4 f 3.2 pg/mL in the normal menopause group. Although the value was lower in the former group, the difference was not significant (Table 2).
Discussion Age-related changes i.n axial bone differ from those in peripheral bone. The former shows a relatively early decrease in BMD after attainment of peak bone mass.2,8 With aging there is an overall decrease in BMD,‘0,15,29 which is accelerated by menopaUse.7.sJ4.23 As reported previously, menopause has diverse effects on the dynamics of bone metabolism.23 Although signiticant postmenopausal increases in Al-P and osteocalcin activity suggest enhanced bone formation potential, the significant rise in U-Hpr/Cr ratio that occurs after menopause indicates increased bone resorption. BMD decreases when the amount of bone resorption surpasses that of bone formation. The main factor implicated in the postmenopausal drop in BMD is a failure to suppress bone resorption caused by decreased serum levels of not only E2 but also e&one (E,). 23 This consequently leads to elevated serum Ca levels, an associated inhibition of paratbyroid hormone function, and suppression of vitamin D activation in the kidney. After menopause, osteoporosis is thought to progress with aging.30 Seeman et al.31 reported that the pathogenesis of osteoporosis after early menopause was similar to that after normal menopause. They found that tbe decrease in BMD was initially greater in women with early menopause than in premenopausal women matched for age, but that the difference between these groups became indistinct after about 10 years. Although still unproven, this theory is widely accepted. The present study, however, demonstrated that L2-4 BMD was significantly lower in the early menopause group, in which about 10 years had passed since menopause, than in the normal menopause group, about 3 years after menopause, although the groups were matched for age and body size. In addition, the mean L2-4 BMD in the 18 subjects in the early menopause group was 0.81 rf:0.65 g/cm2, which was higher than the 90th percentile value for bone fractures (0.770 g/cm2) determined by XR-26, also used in the present study, by the Silver Science Study Group of the Japanese Ministry of Health and Welfare.33 However, individual patient analysis revealed that 10 (55.6%) of the 18 patients in the early menopause group had a L2-4 BMD below the threshold value of 0.770 g/cm2, indicating a high risk of fracture. In contrast, L2~l
229
BMD was below the fracture threshold in only 1 of the 19 patients (5.3%) in the normal menopause group. Subjects who have early menopause, therefore, have an increased risk of developing osteoporosis, as indicated by the absolute value of their L2-4 BMD and the fact that this value exceeded the 90th percentile of the bone fracture threshold. The factors responsible for the low BMD in the early menopause group are unknown and their clarification must await future studies. L24 BMD was lower in the early menopause group than in the normal menopause group, despite lack of a significant difference between the groups in age or body size. Serum levels of E2 and gonadotropins such as LH and FSH were slightly, but not significantly, lower in the early menopause group than in the normal menopause group. The mean D-Pyr/Cr ratio, serving as a bone metabolic marker (D-Pyr is the only deoxy metabolite of pyridinoline), was over threefold higher in the early menopause group than in the normal menopause group. However, although the mean PyrKr ratio was about 27% higher in the early menopause group than in the normal menopause group, the difference between the groups was not significant. In association with the metabolism of bone tissue, i.e., bone resorption, these pyridinolines are excreted in the urine as collagen crosslinks, formed by the breakdown of collagen. Pyridinoline is reported to be derived from bone and cartilage tissue, while its deoxy metabolite, DPyr, is derived from bone tissue.5,6,32 These markers are clinically useful for monitoring the status of bone metabolic diseases, bone metastasis, and endocrinological diseases, as well as assessing the response of these conditions to therapy, but they have recently attracted interest as bone resorption markers that rise remarkably after OPX or in postmenopausal osteoporosis.4*32 A recent report by the authors26 documents studies in which the mean Pyr/Cr ratio in patients undergoing OPX was 30% higher than that in premenopausal control subjects matched for age and body size. In OPX subjects, D-Pyr/Cr ratio did not change significantly compared with control subjects,26 but in postmenopausal patients with osteoporosis, both PyrKr ratio and D-PyrKr ratio were twofold higher than contro1.4*32 Although these were studies in menopausal patients with established osteoporosis, PyrKr ratio has been found to increase by 60% and D-Pyr/Cr by 82% in normal menopausal subjects.34 Hassager et al.’ ’reported a 30%-50% increase in PyrKr ratio 6 months after menopause compared with before menopause. Whether the Pyr/ Cr ratio or the D-PyrKr ratio is more useful as a clinical marker
U-PyridinolineKr nmoVmmol Cr
U-DeoxypyridinolineKr nmoVmmol Cr XrtSE
45
1
40
1
T
35 15 30 10
25
(n-19)
(n-1 8)
(n-19)
(n-1 8)
Figure 2. Urinary markers of bone absorption.
230
H. Ohta et al. Progressive loss of BMD after early menopause
Bone Vol. 18, No. 3 March 1996:227-231
g/cm’
n=19
n=19
1.50
r=O.3193 1.25
Y=o.180+ NS
.
P s . r; .A
.
l.OO-
.
.
??
.
.
??
.
1 .oo
?? . ??
.
??*
:
.
.
.
.
8
??
0.75
yrs
50
0.50
5.071 X
.
.
0.50’ 40
Y=O.996NS
??
.
.
.
-
1.25
;
. 0.75
r=-0.0775 1.606X
? ?
? ?
mon
r
0
24
48
72
96
120
interval after menopause
Figure 3. Relationship
between L24
BMD and age and interval after menopause
is currently unclear, but these values may differ somewhat depending on when urine samples were obtained, the assay method used, and the types of patients studied. Unlike conventional bone metabolic markers, these pyridinolines are regarded by the authors to be able to forecast the risk of a drop in L2-4 BMD in the forthcoming 6 months.24 Although D-Pyr/Cr ratio has been reported to be 11.97 f 2.68 mmoVnmo1 Cr (mean ? SE) in OPX subjects (n = 90),26 the value was abnormally high (18.52 + 3.69 mmol/nmol Cr) in the early menopause group in the present study. The significantly higher value than in the normal menopause group foretells of a further decline in BMD in the future. While menopause-related BMD changes continue up to 10 years after the event, the greatest changes occur in the first or second year; therefore, the fact that an average period since menopause in the normal group was approximately 3 years (mean 34 months) is of importance in this comparative study. As illustrated in Figures 3 and 4, although L24 BMD did not correlate with either age or time after menopause in the normal menopause group, L2-4 BMD in the early menopause group decreased with increasing age (r = -0.7043, p < 0.01) and with the number of years after menopause (r = -0.6107, p < 0.01). Future decreases in BMD, associated with
g/cm2
n=18
1.501]
1.25
0.50-1 30
k-O.7043 Y=l.690p
.
in the normal menopause
group.
increasing age and number of years after menopause, are therefore highly likely in women who have early menopause. There are slight country-specific differences in the criteria defining the cutoff age for early menopause. In the United Kingdom16 and the United Statesi early menopause is defined as menopause at age 40 or before, whereas the cutoff point is 42 years in Japan and 45 years in Argentina.’ Various experimental and clinical studies have addressed potential causes for premature onset of menopause. Autoimmune disease has been implicated as one possible cause, but evidence supporting this or other hypotheses is currently lacking. However, since at least 1%-2% to less than 5% of all women are estimated to have early menopause, the number of patients is considerable. Furthermore, as demonstrated in this study, women with early menopause have lower BMD than those with normal menopause, and about half of the former group have a BMD below the fracture threshold. In addition, the D-Pyr ratio and the negative correlation between BMD and age and the number of years after menopause in the early menopause group indicates a high risk of a future decrease in BMD. Considering the remarkable prolongation of mean life expectancy for women to about 82 years in Japan, an increased incidence of osteoporosis seems inevitable.
n=lf
1.501 r=-0.6107 Y=O.986p-Co.01
1.881X 1.25-
.
1.368X
mon
40
50
age Figure 4. Relationship
between L24
60
0
60
120
180
240
300
360
interval after menopause BMD and age and interval after menopause
in the early menopausal
group.
Bone Vol. 18, No. 3 March 1996:227-231
Acknowledgments:
This work was supported in part by the Ministry of Education of Japan (Grant No. 06671684), and its content was presented at the 1 lth congress of the Japan Society for Bone and Mineral Research in Yokohama, Japan, July 31-August 2, 1993. We express our gratitude to Professor J. Patrick Barron, Tokyo Medical College, for reviewing the manuscript.
References 1. Bagur, A. C. and Mautalen, C. A. Risk for developing osteoporosis in untreated premature menopause. Calcif Tissue Int 51:&7; 1992. 2. Buchanan, J. R., Myers, C., Lloyd, T., and Green R. B., III. Early vertebral trabecular bone loss in normal premenopausal women. J Bone Miner Res 3:583-587; 1988. 3. Cann, C. E., Genant, H. K., Kolb, F. O., and Ettinger, B. Quantitative computed tomography for prediction of vertebral fracture risk. Bone 6: 1-7; 1985. 4. Delmas, P. D., Schletnmer, A., Gineyts, E., Riis, B., and Christiansen, C. Urinary excretion of pyridinoline crosslinks correlates with bone turnover tneawed on iliac crest biopsy in patients with vertebral osteoporosis. J Bone Miner Res 6639-644; 1991. 5. Eyre, D. Collagen cross-linking amino acids, Methods Enzymol 144: 115-139; 1987. 6. Fujimoto, D., Motiguchi, T., Ishida, T., and Hayashi, H. The structure of pyridinoline, a collagen crosslink. Biochem Biophys Res Commun 84:52-57; 1978. 7. Gallagher, J. C., Goldgar, D., and Moy, A. Total bone calcium in normal women: effect of age and menopause status. J Bone Miner Res 2:491496; 1987. 8. Geusens, P., Dequeker, I., Verstraeten, A., and Nijs, J. Age-, sex- and tnenopause-related changes of vertebral and peripheral bone: population study using dual and single photon absorptiometry and radiogrammetry. J Nucl Med 27:154&1549; 1986. 9. Hansen, M. A. Assessment of age and risk factors on bone density and bone turnover in healthy premenopausal women. Osteoporosis Int 4:123-128; 1994. 10. Hansson, T. and Roos, B. Age changes in the bone mineral of the lumbar spine in normal women. Calcif Tissue Int 38:249-251; 1986. 11. Hassager, C., Colwell, A., Assiri, A.M. A., Eastell, R., Russell, R. G. G., and Christiansen, C. Effect of menopause and hormone replacement therapy on urinary excretion of pyridinium cross-links: a longitudinal and cross-sectional study. Clin Endoctinol 37:45-50; 1992. 12. Johnson. B. E., Lucasey, B., Robinson, R. G., and Luke& B. P. Contributing diagnoses in osteoporosis. The value of a complete medical evaluation. Arch Intern Med 149:1069-1072; 1989. 13. Jones, K. P., Ravnikar, V. A., Tulchinsky, D., and Schiff, I. Comparison of bone density in amenorrheic women due to athletics, weight loss, and pretnature menopause. Obstet Gynecol 66:5-8; 1985. 14. Krolner, B. and Pars Nielsen, S. Bone mineral content of the lumbar spine in normal and osteoporotic women: cross-sectional and longitudinal studies. Clin Sci 621329-336; 1982. 15. Matkovic, V., Jelic, T., Wardlaw, G. M., Ihch, J. Z., Gael, P. K., Wright, J. K., Andon, M. B., Smith, K. T., and Heaney, R. P. Timing of peak bone mass in Caucasian females and its implication for the prevention of osteoporosis. I Clin Invest 93:799-808; 1994. 16. Mitchell, A. Too young for the change? Menopause in women under 40. Prof Nurse 5:11&112; 1989. 17. Ohta, H., Nemoto, K., Nozawa, S., and Iizuka, R. Changes in bone mineral content and bone metabolism related to menopause. Acta Obstet Gynaec Jpn 41:1447-1454; 1989 (in Japanese, with English abstract). 18. Ohta, H., Nemoto, K., Nozawa, S., and Iizuka, R. Mechanism of the decrease in metacarpal bone mineral content due to oopherectomy. Acta Obst Gynaec Jpn 41:333-340; 1989 [in Japanese, with English abstract). 19. Ohta, H., Nemoto, K., Nozawa, S., and Iizuka, R. Assessment of osteopenia
Progressive
H. Ohta et al. loss of BMD after early menopause
231
following oophorectomy by quantitative computed tomography and its relation with Ca-regulating hormones. Acta Obstet Gynaec Jpn 41:1471-1478; 1989 (in Japanese, with English abstract). 20. Ohta, H., Nemoto, K., Nozawa, S., and Iizuka, R. Bone mineral loss due to premenopausal oophorectomy assessed by dual photon absorptiometry Acta Obstet Gynaec Jpn 42: 185-191; 1990 (in Japanese, with English abstract). 21. Ohta, H., Makita, K., Suds, Y., Ikeda, T., Masurawa, T., and Nozawa, S. Influence of oophorectomy on semm levels of sex steroids and bone metabolism and assessment of bone mineral density in lumbar trabecular bone by QCT-C value. J Bone Miner Res 7:659-665; 1992. 22. Ohta, H., Masuzawa, T., Ikeda, T., Suds, Y., Makita, K., and Nozawa, S. Which is more osteoporosis-inducing, tnenopause or oophorectomy? Bone Miner 19:273-285; 1992. 23. Ohta, H., Ikeda, T., Masuzawa, T., Makita, K., Suda, Y., and Nozawa, S. Differences in axial bone mineral density, sewn levels of sex steroids, and bone metabolism between postmenopausal and age- and body size-matched premenopausal subjects. Bone 14: 11l-l 16; 1993. 24. Ohta, H., Kotnukai, S., Ikeda, T., Masuzawa, T., Suds, Y., Makita, K., Horiguchi, F., and Nozawa, S. Early diagnosis of osteoporosis and indication of treatment in oophorectomized subjects. J Jpn Menopause Sot 1:202-210; 1993 (in Japanese, with English abstract). 25. Ohta, H. Sex steroid hormones and osteoporosis. Clin Physician 20:1680-1684; 1994 (in Japanese). 26. Ohta, H., Makita, K., Suds, Y., Masuzawa, T., Ikeda, T., Komukai, S., Masuda, A., Yoshimura, Y., Taketomi, S., and Nozawa, S. Urinary levels of pyridinium crosslinks of collagen and lumbar bone mineral density measured by DXA after oophorectomy. J Jpn Menopause Sot 2:201-209; 1994. 27. Part%, A. M. Trabecular bone architecture in the pathogenesis and prevention of fracture. Am J Med 82:68-72; 1987. 28. Raw, P., Hetland, M. L., Overgaatd, K., and Christiansen, C. Premenopausal and postmenopausal changes in bone mineral density of the proximal femur measured by dual-energy X-ray absorptiometry. J Bone Miner Res 9:19751980; 1994. 29. Riggs. B. L., Wahner, H. W., Melton, L. J., III, Richelson, L. S., Judd, H. L., and Offord, K. P. Rates of bone loss in the appendicular and axial skeletons of women. Evidence of substantial vertebral bone loss before menopause. J Clin Invest 77:1487-1491; 1986. 30. Riggs, B. L. and Melton, L. J., III. Medical progress: Involutional osteoporosis. N Engl J Med 314:1676-1686; 1986. 31. Seeman, E., Cooper, M. E., Hopper, I. L., Parkinson, E., McKay, J., and Jerums, G. Effect of early menopause on bone mass in normal women and patients with osteoporosis. Am J Med 85:213-216; 1988. 32. Seibel, M. J., Ratcliffe, A., Cosman, F., Shea, V., Henington, B., Dempster, D., and Lindsay, R. Urinary hydroxy-pytidinium crosslinks of collagen are markers of bone resorption and estrogen efficacy in postmenopausal osteoporosis. Tram Orthop Res Sot 16:S279; 1991. Shiraki, M., Kaneda, S., Nakamura, T., Nakamura, T., Kurokawa, T., Inoue, T., Totnita, A., Morii, H., Fujita, T., Fukase, M., Tsutsuizumi, M., Fukunaga, H., Yamamoto, K., Notimatsu, T., Morita, R., and Orimo, H. Age-related changes in bone mineral density and the fracture threshold. J Bone Miner Met 8:S283; 1990 (in Japanese). Uebelhatt, D., Schlemmer, A., Johansen, J. S., Gineyts, E., Christiansen, C., and Delmas, P. D. Effect of menopause and hormone replacement therapy on the urinary excretion of pytidinium cross-links. J Clin Endocrinol Metab 72~367-373; 1991.
Dare Received: June 19, 1995 Date Revised: October 25, 1995 Dare Accepted: October 31, 1995