J Bone Miner Metab DOI 10.1007/s00774-013-0534-x
ORIGINAL ARTICLE
Relationship between autonomic nervous system activity and bone mineral density in non-medicated perimenopausal women Naoyuki Miyasaka • Mihoko Akiyoshi Toshiro Kubota
•
Received: 13 June 2013 / Accepted: 16 October 2013 Ó The Japanese Society for Bone and Mineral Research and Springer Japan 2013
Abstract The autonomic nervous system (ANS) has attracted attention as a regulator of bone remodeling and the effects of beta-blockers on the prevention of osteoporosis have been studied. However, results are as yet inconclusive and the physiological role of the ANS in bone metabolism has not been clarified. Thus, we investigated the relationship between bone mineral density (BMD) and ANS activity in non-medicated perimenopausal women. ANS activity was evaluated by power spectral analysis of heart rate variability, and overall ANS activity and the balance between sympathetic and parasympathetic nervous activities (SNS and PNS) were quantified. Pre- and postmenopausal subjects were divided into higher or lower overall ANS activity groups, and were also divided into SNS- and PNS-dominant groups. BMD (percentage of young adult mean) was significantly higher in the higher overall ANS group than in the lower group (112.2 ± 16.2 % vs 99.7 ± 14.8 %, p \ 0.05) of premenopausal subjects, but not in postmenopausal subjects (91.5 ± 15.9 % vs 91.0 ± 14.9 %). BMD was significantly higher in the SNS-dominant group than in the PNS-dominant group (94.1 ± 16.3 % vs 88.4 ± 18.8 %, p \ 0.05) of postmenopausal subjects, but not in the premenopausal subjects (103.5 ± 18.4 % vs. 107.2 ± 14.6 %). Our study revealed that ANS influences bone metabolism under
N. Miyasaka (&) Department of Pediatric, Perinatal and Maternal Medicine, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-5819, Japan e-mail: [email protected] M. Akiyoshi T. Kubota Comprehensive Reproductive Medicine, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-5819, Japan
physiological conditions. Thus, it appears to be worthwhile to introduce ANS activity evaluation into the management of bone health in perimenopausal women. Keywords Menopause Bone mineral density Autonomic nervous system Heart rate variability Power spectrum analysis
Introduction Osteoporosis is a skeletal disorder characterized by a low bone mass and structural deterioration of bone tissue. Its consequences are compromised bone strength and an increased risk of fracture. Osteoporosis is more common in women, in which bone is lost rapidly in the first 4-8 years after menopause. Therefore, a multi-faceted approach to the prevention of postmenopausal osteoporosis is important. Bone undergoes remodeling throughout a person’s life and this remodeling was long believed to be regulated by local mechanical and cytokine influences and by the effects of systemic hormones. At the beginning of this century, Ducy et al. [1] reported that leptin, a hormone produced by fat, inhibited bone formation in mice and Takeda et al. [2] demonstrated that this effect was mediated by the sympathetic nervous system (SNS). Since these discoveries, the autonomic nervous system (ANS) has attracted attention as a newly recognized regulator of bone remodeling, and a number of clinical and experimental studies have shown that SNS activation is associated with reduced bone mineral density (BMD) [3]. However, contradictory conclusions have been reached in both animal and clinical studies, specifically in clinical studies involving peri- and postmenopausal women [4–7]. In addition, the relationship between ANS activity and BMD under physiological non-
123
J Bone Miner Metab
medicated conditions is not known because most prior clinical studies were designed to compare BMD and/or fracture risks between beta-blocker users and non-users. Spectral analysis of heart rate variability (HRV) is a non-invasive measure of ANS activity [8] and offers a practical approach to evaluating activities of the SNS and the parasympathetic nervous system (PNS) in clinical research. Accordingly, the present study evaluated resting ANS activity, including overall ANS activity and the balance between SNS and PNS activities in non-medicated perimenopausal women by means of HRV spectral analysis. The purpose of this study was to investigate the relationship between ANS activity and BMD in order to clarify the role of the ANS in controlling bone remodeling in perimenopausal women in physiological states.
digitized with a sampling rate of 1 kHz and the R–R intervals were stored sequentially. Next, the power spectral analysis by means of a fast Fourier transformation was performed on the R–R interval series. The spectral powers were calculated for the following respective frequency bands—the low frequency (0.03–0.15 Hz) power (LP), an indicator of both SNS and PNS activity; the high frequency (0.15–0.5 Hz) power (HP), which reflects solely PNS activity; and total (0.03–0.5 Hz) power (TP) representing the overall ANS activity. In order to assess the balance between SNS and PNS activities, we used LP/HP and HP/ TP as indicators of SNS and PNS activities (SNA and PNA), respectively [10]. Statistical differences between groups were assessed using Student’s unpaired t test for parametric measures and the Mann–Whitney U test for non-parametric measures, and p values \0.05 were considered statistically significant. Data are expressed as mean ± SD or medians (range).
Materials and methods The subjects were recruited consecutively from among the patients who visited our climacteric clinic. Those who exercised regularly, smoked, or drank heavily, those who were diagnosed with diabetes mellitus, hypertension, cardiovascular diseases, psychiatric disease or endocrine disorders not related to menopause, and those who were taking medications were excluded. The present study involved 90 premenopausal women (47.9 ± 4.0 years) and 117 postmenopausal women (53.4 ± 6.0 years). The study protocol was approved by the medical ethics committee of Tokyo Medical and Dental University and was carried out in accordance with the Declaration of Helsinki. The subjects completed a standardized health questionnaire including medical history, medications, menstrual history, smoking habits and alcohol consumption. In postmenopausal women, more than 6 months had passed since the last menstruation. After height and weight measurements had been obtained, the percentage of body fat was determined employing a bioelectrical impedance analyzer and a blood sample was then drawn from the antecubital vein. BMD was measured at the lumbar spine by dual-energy X-ray absorptiometry and the data were expressed as a percentage of the young adult mean (%YAM). ANS function was evaluated by analyzing the electrocardiogram (ECG) R–R interval variability. The procedures for ECG measurement and power spectrum analysis of R–R interval variability were described in detail elsewhere [9]. Briefly, the subjects were allowed to rest for at least 20 min prior to the measurement, and the ECG was then continuously monitored and recorded for 5 min during supine rest. ECG measurements were always performed in the morning to avoid circadian variation. ECG data were
123
Results There were no significant differences between pre- and postmenopausal subjects in height, weight, body mass index (BMI), or percentage of body fat. BMD was significantly higher in premenopausal than in postmenopausal subjects (105.4 ± 16.5 % vs 91.3 ± 15.3 %, p \ 0.01). Estradiol and follicular stimulating hormone (FSH) in premenopausal subjects were significantly higher and lower, respectively, than those in postmenopausal subjects. The TP showed a skewed distribution, and its median value in premenopausal subjects was significantly higher than that in postmenopausal subjects (334 vs 242 ms2, p \ 0.05), whereas no significant differences were
Table 1 Comparison between pre- and postmenopausal subjects Pre-menopause (n = 90) Age (years) 2
47.9 (4.0)
Post-menopause (n = 117) 53.4 (6.0)
P \0.0001
TP (ms )
334 (25–7,851)
242 (35–5,600)
0.042
LP/HP (a.u.)
0.86 (0.12–7.49)
0.80 (0.06–11.84)
0.810
HP/TP (a.u.)
0.54 (0.12–0.90)
0.56 (0.08–0.95)
Height (cm)
0.810
158.3 (5.8)
157.5 (5.6)
0.323
54.9 (9.9)
54.0 (8.3)
0.483
21.9 (4.0) 27.1 (5.3)
21.8 (3.5) 28.5 (5.2)
0.795 0.153
BMD (%YAM)
105.4 (16.5)
91.3 (15.3)
\0.0001
Estradiol (pg/ mL)
189.6 (162.0)
33.7 (36.7)
\0.0001
FSH (IU/mL)
13.8 (13.6)
91.1 (38.2)
\0.0001
BW (kg) 2
BMI (kg/m ) Body fat (%)
J Bone Miner Metab Table 2 Comparison between higher and lower overall ANS activity groups in pre- and postmenopausal subjects Overall autonomic nervous activity
Pre-menopause (n = 90) LOW group
Post-menopause (n = 117)
HIGH group
p
LOW group
HIGH group
p
TP (ms2)
174 (25–320)
730 (348–7,851) \0.0001
130 (35–242)
489 (244–5,600) \0.0001
LP/HP (a.u.)
0.99 (0.21–6.65)
0.68 (0.12–7.49)
0.0345
0.90 (0.06–11.84)
0.74 (0.07–7.65)
0.2546
HP/TP (a.u.)
0.50 (0.13–0.83)
0.60 (0.12–0.90)
0.0345
0.53 (0.08–0.95)
0.58 (0.12–0.93)
0.2546
Height (cm)
159.0 (5.7)
0.2715
157.8 (5.4)
BW (kg)
54.5 (10.6)
55.4 (9.2)
0.6927
55.0 (9.2)
53.1 (0.2143)
0.2143
BMI (kg/m2)
22.0 (4.3)
21.9 (3.6)
0.9719
22.2 (4.1)
21.5 (2.9)
0.3053
27.7 (5.1) 183.1 (175.3)
26.3 (5.6) 197.6 (147.0)
0.3769 0.7461
29.0 (5.8) 18.9 (20.8)
28.0 (4.5) 29.7 (43.7)
0.4307 0.0925
15.1 (15.5)
12.1 (10.9)
0.4245
93.5 (38.9)
88.9 (37.7)
0.5335
Body fat (%) Estradiol (pg/mL) FSH (IU/mL)
157.6 (5.8)
157.2 (5.9)
0.6203
Fig. 1 a In premenopausal subjects, BMD was significantly higher in the HIGH group (TP [334 ms2) than in the LOW group (TP \334 ms2) (112.2 ± 16.2 % vs 99.7 ± 14.8 %, p \ 0.05). b In contrast, no significant difference was observed in postmenopausal subjects (91.5 ± 15.9 % vs 91.0 ± 14.9 %, respectively). c In premenopausal subjects, there was no significant difference in BMD between the SNS- and PNS-dominant groups (103.5 ± 18.4 % vs 107.2 ± 14.6 %). d In contrast, in postmenopausal subjects, BMD was significantly higher in the SNS-dominant group than in the PNS-dominant group (94.1 ± 16.3 % vs 88.4 ± 18.8 %, p \ 0.05)
observed in either LP/HP or HP/TP between the two groups (Table 1). To identify potential influences of overall ANS activity levels on BMD in pre- and postmenopausal subjects separately, we divided the subjects into two subgroups based on the TP, i.e., the LOW group (TP \334 ms2 in premenopausal women and \242 ms2 in postmenopausal women) and HIGH group (TP [334 ms2 in premenopausal women and [242 ms2 in postmenopausal women). There were no significant differences in height, weight, BMI, percentage of body fat, plasma estradiol, or FSH between
the LOW and HIGH groups of both pre- and postmenopausal subjects (Table 2). In premenopausal subjects, BMD was significantly higher in the HIGH than in the LOW group (112.2 ± 16.2 % vs 99.7 ± 14.8 %, p \ 0.05) (Fig. 1a), which were also significantly different even after adjustment for age and BMI (111.7 ± 15.1 vs 99.9 ± 15.2, p \ 0.05). In contrast, no significant difference was observed in the postmenopausal subjects (91.5 ± 15.9 % vs 91.0 ± 14.9 %, respectively) (Fig. 1b). To assess potential influences of the balance between SNS and PNS activities on BMD in pre- and
123
J Bone Miner Metab Table 3 Comparison between SNS- and PNS-dominant groups in pre- and postmenopausal subjects Balance of ANS activity
Pre-menopause (n = 90) SNS dominant
PNS dominant
Post-menopause (n = 117) p
SNS dominant
PNS dominant
p
LP/HP (a.u.)
1.55 (0.87–7.49)
0.44 (0.12–0.85)
\0.0001
1.43 (0.80–11.84)
0.44 (0.06–0.79)
\0.0001
HP/TP (a.u.)
0.39 (0.12–0.54)
0.69 (0.54–0.90)
\0.0001
0.41 (0.08–0.56)
0.69 (0.56–0.95)
\0.0001
TP (ms2)
260 (25–4,200)
440 (56–7,851)
0.1005
230 (35–5,600)
277 (80–3,202)
0.2251
Height (cm)
158.2 (5.3)
0.8094
157.3 (5.9)
157.7 (5.4)
BW (kg)
56.4 (11.5)
53.6 (8.0)
0.2148
54.2 (7.0)
53.8 (9.6)
0.7856
BMI (kg/m2)
22.4 (4.3)
21.5 (3.7)
0.3042
22.0 (3.0)
21.6 (4.0)
0.6358
28.3 (6.3) 164.0 (145.5)
25.8 (3.7) 211.6 (174.6)
0.0928 0.2867
28.7 (4.7) 25.6 (35.4)
28.2 (5.8) 23.3 (34.2)
0.7398 0.7298
17.2 (17.6)
10.8 (8.2)
0.0831
88.7 (34.8)
93.4 (41.2)
0.5257
Body fat (%) Estradiol (pg/mL) FSH (IU/mL)
158.5 (6.3)
postmenopausal subjects separately, we also divided the subjects into two subgroups based on the LP/HP and HP/ TP, i.e., SNS dominant (LP/HP is higher and HP/TP is lower than 50th percentile) and PNS dominant (LP/HP is lower and HP/TP is higher than 50th percentile). There were no significant differences in height, weight, BMI, percentage of body fat, plasma estradiol, or FSH between the SNS and PNS dominant groups of both pre- and postmenopausal subjects (Table 3). In premenopausal subjects, no significant difference was observed in BMD between the SNS- and PNS-dominant groups (103.5 ± 18.4 % vs 107.2 ± 14.6 %) (Fig. 1c). However, in postmenopausal subjects, BMD was significantly higher in the SNS-dominant group than in the PNS-dominant group (94.1 ± 16.3 % vs 88.4 ± 18.8 %, p \ 0.05) (Fig. 1d); BMD was also significantly different even after adjustment for age and BMI (93.5 ± 15.5 vs 89.1 ± 12.0, p \ 0.05).
Discussion Unlike previous clinical studies in which BMD and/or fracture risks were compared between beta-blocker users (i.e., patients with cardiovascular diseases) and non-users, we studied subjects with neither complications nor medication use to clarify the relationship between the ANS and BMD under physiological conditions in perimenopausal women. Furthermore, we analyzed pre- and postmenopausal subjects separately because physical and mental conditions are known to be altered after menopause. In order to evaluate ANS activities quantitatively, we employed the power spectral analysis of ECG R-R interval variability in the resting state, a technique which has been applied under various physiological conditions and in a range of clinical settings. The most striking advantage of this method is that individual SNS and PNS activities can be estimated by the spectral power of each frequency band,
123
0.7322
and the validity of this approach has been confirmed by pharmacological blockade experiments with atropine, a parasympathetic muscarinic antagonist, and propranolol, a beta-adrenoceptor antagonist [10]. Therefore, in this study, ANS activity was evaluated from two perspectives, i.e., the overall ANS activity and the balance between SNS and PNS activities. One of the noteworthy findings of our study was that higher overall ANS activity was associated with higher BMD, which has not been described in any of the previous reports. In premenopausal subjects, BMD was significantly higher in the HIGH than in the LOW group, although there were no significant differences in other factors such as BMI, percentage of body fat, or plasma estradiol levels between these two groups. A similar difference was also found between pre- and postmenopausal subjects, with overall SNS activity and BMD both being significantly decreased in the postmenopausal as compared to the premenopausal subjects. Although the precise mechanism underlying the association between overall ANS activity and BMD is not known, our data imply that bone remodeling is partly controlled directly by overall ANS activities, and that reduced overall ANS activity might contribute, together with decreased estrogen, to postmenopausal bone loss. Another possible explanation for these results is an indirect relationship with physical activity levels because physical exercise is known to increase overall ANS activity [11] and to correlate positively with BMD [12]. On the contrary, no such relationship was present in the postmenopausal subjects, probably because the influence of overall ANS activity has diminished as compared to those of other factors due to significantly reduced overall ANS activity. Another noteworthy finding of our study was that the balance between SNS and PNS activities did not significantly influence BMD in premenopausal subjects and that BMD in the SNS-dominant group was significantly higher
J Bone Miner Metab
than that in the PNS-dominant group of postmenopausal subjects. These findings were unexpected because previous studies have shown SNS activation to be associated with reduced bone mass [3]. Our data imply that the SNS plays a relatively limited role in the control of bone remodeling under physiological conditions as compared to other factors such as humoral, nutritional, and mechanical factors. This may explain why the conclusions of previous clinical studies on the effects of beta-blocker administration for the prevention of osteoporosis have been controversial. Higher BMD in the SNS-dominant postmenopausal group may be associated with most such subjects, at least in our present study, not being osteoporotic. SNS activity is assumed to be increased as a result of negative feedback in non-osteoporotic postmenopausal women. A limitation of our study is that multivariate analysis was not performed due to lack of quantitative data on confounding factors such as physical activity, nutritional status and life style, and also due to the relatively small number of subjects. Therefore, the relative importance of the ANS among a number of factors which regulate bone remodeling is not clear in our study. However, our study revealed that ANS influences BMD independently of BMI, body fat percentage, and plasma estradiol concentrations. In conclusion, we have, for the first time, demonstrated that overall ANS activity contributes to the regulation of BMD under physiological conditions in perimenopausal women. Although this is a preliminary study with a small number of subjects, it appears to be worthwhile to introduce ANS activity evaluation into the management of bone health in perimenopausal women. Conflict of interest
All authors have no conflict of interest.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
bone formation through a hypothalamic relay: a central control of bone mass. Cell 100:197–207 Takeda S, Elefteriou F, Levasseur R, Liu X, Zhao L, Parker KL, Amstrong D, Ducy P, Karsenty G (2002) Leptin regulates bone formation via the sympathetic nervous system. Cell 111:305–317 He JY, Jiang LS, Dai LY (2011) The roles of the sympathetic nervous system in osteoporotic diseases: a review of experimental and clinical studies. Ageing Res Rev 10:253–263 Rejnmark L, Vestergaard P, Kassem M, Christoffersen BR, Kolthoff N, Brixen K, Mosekilde L (2004) Fracture risk in perimenopausal women treated with beta-blockers. Calcif Tissue Int 75:365–372 Levasseur R, Dargent-Molina P, Sabatier JP, Marcelli C, Breart G (2005) Beta-blocker use, bone mineral density, and fracture risk in older women: results from the Epidemiologie de l’Osteoporose prospective study. J Am Geriatr Soc 53:550–552 Reid IR, Gamble GD, Grey AB, Black DM, Ensrud KE, Browner WS, Bauer DC (2005) beta-blocker use, BMD, and fractures in the study of osteoporotic fractures. J Bone Miner Res 20:613–618 Sosa M, Saavedra P, Gomez de Tejada MJ, Mosquera J, PerezCano R, Olmos JM, Munoz-Torres M, Amerigo ML, Moro MJ, Diaz-Curiel M, Alegre J, Malouf J, Del Pino J, Nogues X, Torrijos A, GIUMO Cooperative Group (2011) Beta-blocker use is associated with fragility fractures in postmenopausal women with coronary heart disease. Aging Clin Exp Res 23:112–117 Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (1996) Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation 93:1043–1065 Kimura T, Matsumoto T, Akiyoshi M, Owa Y, Miyasaka N, Aso T, Moritani T (2006) Body fat and blood lipids in postmenopausal women are related to resting autonomic nervous system activity. Eur J Appl Physiol 97:542–547 Matsumoto T, Miyawaki T, Ue H, Kanda T, Zenji C, Moritani T (1999) Autonomic responsiveness to acute cold exposure in obese and non-obese young women. Int J Obes Relat Metab Disord 23:793–800 Amano M, Kanda T, Ue H, Moritani T (2001) Exercise training and autonomic nervous system activity in obese individuals. Med Sci Sports Exerc 33:1287–1291 Kim KZ, Shin A, Lee J, Myung SK, Kim J (2012) The beneficial effect of leisure-time physical activity on bone mineral density in pre- and postmenopausal women. Calcif Tissue Int 91:178–185
References 1. Ducy P, Amling M, Takeda S, Priemel M, Schilling AF, Beil FT, Shen J, Vinson C, Rueger JM, Karsenty G (2000) Leptin inhibits
123
ORIGINAL ARTICLE
Relationship between autonomic nervous system activity and bone mineral density in non-medicated perimenopausal women Naoyuki Miyasaka • Mihoko Akiyoshi Toshiro Kubota
•
Received: 13 June 2013 / Accepted: 16 October 2013 Ó The Japanese Society for Bone and Mineral Research and Springer Japan 2013
Abstract The autonomic nervous system (ANS) has attracted attention as a regulator of bone remodeling and the effects of beta-blockers on the prevention of osteoporosis have been studied. However, results are as yet inconclusive and the physiological role of the ANS in bone metabolism has not been clarified. Thus, we investigated the relationship between bone mineral density (BMD) and ANS activity in non-medicated perimenopausal women. ANS activity was evaluated by power spectral analysis of heart rate variability, and overall ANS activity and the balance between sympathetic and parasympathetic nervous activities (SNS and PNS) were quantified. Pre- and postmenopausal subjects were divided into higher or lower overall ANS activity groups, and were also divided into SNS- and PNS-dominant groups. BMD (percentage of young adult mean) was significantly higher in the higher overall ANS group than in the lower group (112.2 ± 16.2 % vs 99.7 ± 14.8 %, p \ 0.05) of premenopausal subjects, but not in postmenopausal subjects (91.5 ± 15.9 % vs 91.0 ± 14.9 %). BMD was significantly higher in the SNS-dominant group than in the PNS-dominant group (94.1 ± 16.3 % vs 88.4 ± 18.8 %, p \ 0.05) of postmenopausal subjects, but not in the premenopausal subjects (103.5 ± 18.4 % vs. 107.2 ± 14.6 %). Our study revealed that ANS influences bone metabolism under
N. Miyasaka (&) Department of Pediatric, Perinatal and Maternal Medicine, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-5819, Japan e-mail: [email protected] M. Akiyoshi T. Kubota Comprehensive Reproductive Medicine, Graduate School, Tokyo Medical and Dental University, 1-5-45 Yushima, Bunkyo-ku, Tokyo 113-5819, Japan
physiological conditions. Thus, it appears to be worthwhile to introduce ANS activity evaluation into the management of bone health in perimenopausal women. Keywords Menopause Bone mineral density Autonomic nervous system Heart rate variability Power spectrum analysis
Introduction Osteoporosis is a skeletal disorder characterized by a low bone mass and structural deterioration of bone tissue. Its consequences are compromised bone strength and an increased risk of fracture. Osteoporosis is more common in women, in which bone is lost rapidly in the first 4-8 years after menopause. Therefore, a multi-faceted approach to the prevention of postmenopausal osteoporosis is important. Bone undergoes remodeling throughout a person’s life and this remodeling was long believed to be regulated by local mechanical and cytokine influences and by the effects of systemic hormones. At the beginning of this century, Ducy et al. [1] reported that leptin, a hormone produced by fat, inhibited bone formation in mice and Takeda et al. [2] demonstrated that this effect was mediated by the sympathetic nervous system (SNS). Since these discoveries, the autonomic nervous system (ANS) has attracted attention as a newly recognized regulator of bone remodeling, and a number of clinical and experimental studies have shown that SNS activation is associated with reduced bone mineral density (BMD) [3]. However, contradictory conclusions have been reached in both animal and clinical studies, specifically in clinical studies involving peri- and postmenopausal women [4–7]. In addition, the relationship between ANS activity and BMD under physiological non-
123
J Bone Miner Metab
medicated conditions is not known because most prior clinical studies were designed to compare BMD and/or fracture risks between beta-blocker users and non-users. Spectral analysis of heart rate variability (HRV) is a non-invasive measure of ANS activity [8] and offers a practical approach to evaluating activities of the SNS and the parasympathetic nervous system (PNS) in clinical research. Accordingly, the present study evaluated resting ANS activity, including overall ANS activity and the balance between SNS and PNS activities in non-medicated perimenopausal women by means of HRV spectral analysis. The purpose of this study was to investigate the relationship between ANS activity and BMD in order to clarify the role of the ANS in controlling bone remodeling in perimenopausal women in physiological states.
digitized with a sampling rate of 1 kHz and the R–R intervals were stored sequentially. Next, the power spectral analysis by means of a fast Fourier transformation was performed on the R–R interval series. The spectral powers were calculated for the following respective frequency bands—the low frequency (0.03–0.15 Hz) power (LP), an indicator of both SNS and PNS activity; the high frequency (0.15–0.5 Hz) power (HP), which reflects solely PNS activity; and total (0.03–0.5 Hz) power (TP) representing the overall ANS activity. In order to assess the balance between SNS and PNS activities, we used LP/HP and HP/ TP as indicators of SNS and PNS activities (SNA and PNA), respectively [10]. Statistical differences between groups were assessed using Student’s unpaired t test for parametric measures and the Mann–Whitney U test for non-parametric measures, and p values \0.05 were considered statistically significant. Data are expressed as mean ± SD or medians (range).
Materials and methods The subjects were recruited consecutively from among the patients who visited our climacteric clinic. Those who exercised regularly, smoked, or drank heavily, those who were diagnosed with diabetes mellitus, hypertension, cardiovascular diseases, psychiatric disease or endocrine disorders not related to menopause, and those who were taking medications were excluded. The present study involved 90 premenopausal women (47.9 ± 4.0 years) and 117 postmenopausal women (53.4 ± 6.0 years). The study protocol was approved by the medical ethics committee of Tokyo Medical and Dental University and was carried out in accordance with the Declaration of Helsinki. The subjects completed a standardized health questionnaire including medical history, medications, menstrual history, smoking habits and alcohol consumption. In postmenopausal women, more than 6 months had passed since the last menstruation. After height and weight measurements had been obtained, the percentage of body fat was determined employing a bioelectrical impedance analyzer and a blood sample was then drawn from the antecubital vein. BMD was measured at the lumbar spine by dual-energy X-ray absorptiometry and the data were expressed as a percentage of the young adult mean (%YAM). ANS function was evaluated by analyzing the electrocardiogram (ECG) R–R interval variability. The procedures for ECG measurement and power spectrum analysis of R–R interval variability were described in detail elsewhere [9]. Briefly, the subjects were allowed to rest for at least 20 min prior to the measurement, and the ECG was then continuously monitored and recorded for 5 min during supine rest. ECG measurements were always performed in the morning to avoid circadian variation. ECG data were
123
Results There were no significant differences between pre- and postmenopausal subjects in height, weight, body mass index (BMI), or percentage of body fat. BMD was significantly higher in premenopausal than in postmenopausal subjects (105.4 ± 16.5 % vs 91.3 ± 15.3 %, p \ 0.01). Estradiol and follicular stimulating hormone (FSH) in premenopausal subjects were significantly higher and lower, respectively, than those in postmenopausal subjects. The TP showed a skewed distribution, and its median value in premenopausal subjects was significantly higher than that in postmenopausal subjects (334 vs 242 ms2, p \ 0.05), whereas no significant differences were
Table 1 Comparison between pre- and postmenopausal subjects Pre-menopause (n = 90) Age (years) 2
47.9 (4.0)
Post-menopause (n = 117) 53.4 (6.0)
P \0.0001
TP (ms )
334 (25–7,851)
242 (35–5,600)
0.042
LP/HP (a.u.)
0.86 (0.12–7.49)
0.80 (0.06–11.84)
0.810
HP/TP (a.u.)
0.54 (0.12–0.90)
0.56 (0.08–0.95)
Height (cm)
0.810
158.3 (5.8)
157.5 (5.6)
0.323
54.9 (9.9)
54.0 (8.3)
0.483
21.9 (4.0) 27.1 (5.3)
21.8 (3.5) 28.5 (5.2)
0.795 0.153
BMD (%YAM)
105.4 (16.5)
91.3 (15.3)
\0.0001
Estradiol (pg/ mL)
189.6 (162.0)
33.7 (36.7)
\0.0001
FSH (IU/mL)
13.8 (13.6)
91.1 (38.2)
\0.0001
BW (kg) 2
BMI (kg/m ) Body fat (%)
J Bone Miner Metab Table 2 Comparison between higher and lower overall ANS activity groups in pre- and postmenopausal subjects Overall autonomic nervous activity
Pre-menopause (n = 90) LOW group
Post-menopause (n = 117)
HIGH group
p
LOW group
HIGH group
p
TP (ms2)
174 (25–320)
730 (348–7,851) \0.0001
130 (35–242)
489 (244–5,600) \0.0001
LP/HP (a.u.)
0.99 (0.21–6.65)
0.68 (0.12–7.49)
0.0345
0.90 (0.06–11.84)
0.74 (0.07–7.65)
0.2546
HP/TP (a.u.)
0.50 (0.13–0.83)
0.60 (0.12–0.90)
0.0345
0.53 (0.08–0.95)
0.58 (0.12–0.93)
0.2546
Height (cm)
159.0 (5.7)
0.2715
157.8 (5.4)
BW (kg)
54.5 (10.6)
55.4 (9.2)
0.6927
55.0 (9.2)
53.1 (0.2143)
0.2143
BMI (kg/m2)
22.0 (4.3)
21.9 (3.6)
0.9719
22.2 (4.1)
21.5 (2.9)
0.3053
27.7 (5.1) 183.1 (175.3)
26.3 (5.6) 197.6 (147.0)
0.3769 0.7461
29.0 (5.8) 18.9 (20.8)
28.0 (4.5) 29.7 (43.7)
0.4307 0.0925
15.1 (15.5)
12.1 (10.9)
0.4245
93.5 (38.9)
88.9 (37.7)
0.5335
Body fat (%) Estradiol (pg/mL) FSH (IU/mL)
157.6 (5.8)
157.2 (5.9)
0.6203
Fig. 1 a In premenopausal subjects, BMD was significantly higher in the HIGH group (TP [334 ms2) than in the LOW group (TP \334 ms2) (112.2 ± 16.2 % vs 99.7 ± 14.8 %, p \ 0.05). b In contrast, no significant difference was observed in postmenopausal subjects (91.5 ± 15.9 % vs 91.0 ± 14.9 %, respectively). c In premenopausal subjects, there was no significant difference in BMD between the SNS- and PNS-dominant groups (103.5 ± 18.4 % vs 107.2 ± 14.6 %). d In contrast, in postmenopausal subjects, BMD was significantly higher in the SNS-dominant group than in the PNS-dominant group (94.1 ± 16.3 % vs 88.4 ± 18.8 %, p \ 0.05)
observed in either LP/HP or HP/TP between the two groups (Table 1). To identify potential influences of overall ANS activity levels on BMD in pre- and postmenopausal subjects separately, we divided the subjects into two subgroups based on the TP, i.e., the LOW group (TP \334 ms2 in premenopausal women and \242 ms2 in postmenopausal women) and HIGH group (TP [334 ms2 in premenopausal women and [242 ms2 in postmenopausal women). There were no significant differences in height, weight, BMI, percentage of body fat, plasma estradiol, or FSH between
the LOW and HIGH groups of both pre- and postmenopausal subjects (Table 2). In premenopausal subjects, BMD was significantly higher in the HIGH than in the LOW group (112.2 ± 16.2 % vs 99.7 ± 14.8 %, p \ 0.05) (Fig. 1a), which were also significantly different even after adjustment for age and BMI (111.7 ± 15.1 vs 99.9 ± 15.2, p \ 0.05). In contrast, no significant difference was observed in the postmenopausal subjects (91.5 ± 15.9 % vs 91.0 ± 14.9 %, respectively) (Fig. 1b). To assess potential influences of the balance between SNS and PNS activities on BMD in pre- and
123
J Bone Miner Metab Table 3 Comparison between SNS- and PNS-dominant groups in pre- and postmenopausal subjects Balance of ANS activity
Pre-menopause (n = 90) SNS dominant
PNS dominant
Post-menopause (n = 117) p
SNS dominant
PNS dominant
p
LP/HP (a.u.)
1.55 (0.87–7.49)
0.44 (0.12–0.85)
\0.0001
1.43 (0.80–11.84)
0.44 (0.06–0.79)
\0.0001
HP/TP (a.u.)
0.39 (0.12–0.54)
0.69 (0.54–0.90)
\0.0001
0.41 (0.08–0.56)
0.69 (0.56–0.95)
\0.0001
TP (ms2)
260 (25–4,200)
440 (56–7,851)
0.1005
230 (35–5,600)
277 (80–3,202)
0.2251
Height (cm)
158.2 (5.3)
0.8094
157.3 (5.9)
157.7 (5.4)
BW (kg)
56.4 (11.5)
53.6 (8.0)
0.2148
54.2 (7.0)
53.8 (9.6)
0.7856
BMI (kg/m2)
22.4 (4.3)
21.5 (3.7)
0.3042
22.0 (3.0)
21.6 (4.0)
0.6358
28.3 (6.3) 164.0 (145.5)
25.8 (3.7) 211.6 (174.6)
0.0928 0.2867
28.7 (4.7) 25.6 (35.4)
28.2 (5.8) 23.3 (34.2)
0.7398 0.7298
17.2 (17.6)
10.8 (8.2)
0.0831
88.7 (34.8)
93.4 (41.2)
0.5257
Body fat (%) Estradiol (pg/mL) FSH (IU/mL)
158.5 (6.3)
postmenopausal subjects separately, we also divided the subjects into two subgroups based on the LP/HP and HP/ TP, i.e., SNS dominant (LP/HP is higher and HP/TP is lower than 50th percentile) and PNS dominant (LP/HP is lower and HP/TP is higher than 50th percentile). There were no significant differences in height, weight, BMI, percentage of body fat, plasma estradiol, or FSH between the SNS and PNS dominant groups of both pre- and postmenopausal subjects (Table 3). In premenopausal subjects, no significant difference was observed in BMD between the SNS- and PNS-dominant groups (103.5 ± 18.4 % vs 107.2 ± 14.6 %) (Fig. 1c). However, in postmenopausal subjects, BMD was significantly higher in the SNS-dominant group than in the PNS-dominant group (94.1 ± 16.3 % vs 88.4 ± 18.8 %, p \ 0.05) (Fig. 1d); BMD was also significantly different even after adjustment for age and BMI (93.5 ± 15.5 vs 89.1 ± 12.0, p \ 0.05).
Discussion Unlike previous clinical studies in which BMD and/or fracture risks were compared between beta-blocker users (i.e., patients with cardiovascular diseases) and non-users, we studied subjects with neither complications nor medication use to clarify the relationship between the ANS and BMD under physiological conditions in perimenopausal women. Furthermore, we analyzed pre- and postmenopausal subjects separately because physical and mental conditions are known to be altered after menopause. In order to evaluate ANS activities quantitatively, we employed the power spectral analysis of ECG R-R interval variability in the resting state, a technique which has been applied under various physiological conditions and in a range of clinical settings. The most striking advantage of this method is that individual SNS and PNS activities can be estimated by the spectral power of each frequency band,
123
0.7322
and the validity of this approach has been confirmed by pharmacological blockade experiments with atropine, a parasympathetic muscarinic antagonist, and propranolol, a beta-adrenoceptor antagonist [10]. Therefore, in this study, ANS activity was evaluated from two perspectives, i.e., the overall ANS activity and the balance between SNS and PNS activities. One of the noteworthy findings of our study was that higher overall ANS activity was associated with higher BMD, which has not been described in any of the previous reports. In premenopausal subjects, BMD was significantly higher in the HIGH than in the LOW group, although there were no significant differences in other factors such as BMI, percentage of body fat, or plasma estradiol levels between these two groups. A similar difference was also found between pre- and postmenopausal subjects, with overall SNS activity and BMD both being significantly decreased in the postmenopausal as compared to the premenopausal subjects. Although the precise mechanism underlying the association between overall ANS activity and BMD is not known, our data imply that bone remodeling is partly controlled directly by overall ANS activities, and that reduced overall ANS activity might contribute, together with decreased estrogen, to postmenopausal bone loss. Another possible explanation for these results is an indirect relationship with physical activity levels because physical exercise is known to increase overall ANS activity [11] and to correlate positively with BMD [12]. On the contrary, no such relationship was present in the postmenopausal subjects, probably because the influence of overall ANS activity has diminished as compared to those of other factors due to significantly reduced overall ANS activity. Another noteworthy finding of our study was that the balance between SNS and PNS activities did not significantly influence BMD in premenopausal subjects and that BMD in the SNS-dominant group was significantly higher
J Bone Miner Metab
than that in the PNS-dominant group of postmenopausal subjects. These findings were unexpected because previous studies have shown SNS activation to be associated with reduced bone mass [3]. Our data imply that the SNS plays a relatively limited role in the control of bone remodeling under physiological conditions as compared to other factors such as humoral, nutritional, and mechanical factors. This may explain why the conclusions of previous clinical studies on the effects of beta-blocker administration for the prevention of osteoporosis have been controversial. Higher BMD in the SNS-dominant postmenopausal group may be associated with most such subjects, at least in our present study, not being osteoporotic. SNS activity is assumed to be increased as a result of negative feedback in non-osteoporotic postmenopausal women. A limitation of our study is that multivariate analysis was not performed due to lack of quantitative data on confounding factors such as physical activity, nutritional status and life style, and also due to the relatively small number of subjects. Therefore, the relative importance of the ANS among a number of factors which regulate bone remodeling is not clear in our study. However, our study revealed that ANS influences BMD independently of BMI, body fat percentage, and plasma estradiol concentrations. In conclusion, we have, for the first time, demonstrated that overall ANS activity contributes to the regulation of BMD under physiological conditions in perimenopausal women. Although this is a preliminary study with a small number of subjects, it appears to be worthwhile to introduce ANS activity evaluation into the management of bone health in perimenopausal women. Conflict of interest
All authors have no conflict of interest.
2.
3.
4.
5.
6.
7.
8.
9.
10.
11.
12.
bone formation through a hypothalamic relay: a central control of bone mass. Cell 100:197–207 Takeda S, Elefteriou F, Levasseur R, Liu X, Zhao L, Parker KL, Amstrong D, Ducy P, Karsenty G (2002) Leptin regulates bone formation via the sympathetic nervous system. Cell 111:305–317 He JY, Jiang LS, Dai LY (2011) The roles of the sympathetic nervous system in osteoporotic diseases: a review of experimental and clinical studies. Ageing Res Rev 10:253–263 Rejnmark L, Vestergaard P, Kassem M, Christoffersen BR, Kolthoff N, Brixen K, Mosekilde L (2004) Fracture risk in perimenopausal women treated with beta-blockers. Calcif Tissue Int 75:365–372 Levasseur R, Dargent-Molina P, Sabatier JP, Marcelli C, Breart G (2005) Beta-blocker use, bone mineral density, and fracture risk in older women: results from the Epidemiologie de l’Osteoporose prospective study. J Am Geriatr Soc 53:550–552 Reid IR, Gamble GD, Grey AB, Black DM, Ensrud KE, Browner WS, Bauer DC (2005) beta-blocker use, BMD, and fractures in the study of osteoporotic fractures. J Bone Miner Res 20:613–618 Sosa M, Saavedra P, Gomez de Tejada MJ, Mosquera J, PerezCano R, Olmos JM, Munoz-Torres M, Amerigo ML, Moro MJ, Diaz-Curiel M, Alegre J, Malouf J, Del Pino J, Nogues X, Torrijos A, GIUMO Cooperative Group (2011) Beta-blocker use is associated with fragility fractures in postmenopausal women with coronary heart disease. Aging Clin Exp Res 23:112–117 Task Force of the European Society of Cardiology and the North American Society of Pacing and Electrophysiology (1996) Heart rate variability: standards of measurement, physiological interpretation and clinical use. Circulation 93:1043–1065 Kimura T, Matsumoto T, Akiyoshi M, Owa Y, Miyasaka N, Aso T, Moritani T (2006) Body fat and blood lipids in postmenopausal women are related to resting autonomic nervous system activity. Eur J Appl Physiol 97:542–547 Matsumoto T, Miyawaki T, Ue H, Kanda T, Zenji C, Moritani T (1999) Autonomic responsiveness to acute cold exposure in obese and non-obese young women. Int J Obes Relat Metab Disord 23:793–800 Amano M, Kanda T, Ue H, Moritani T (2001) Exercise training and autonomic nervous system activity in obese individuals. Med Sci Sports Exerc 33:1287–1291 Kim KZ, Shin A, Lee J, Myung SK, Kim J (2012) The beneficial effect of leisure-time physical activity on bone mineral density in pre- and postmenopausal women. Calcif Tissue Int 91:178–185
References 1. Ducy P, Amling M, Takeda S, Priemel M, Schilling AF, Beil FT, Shen J, Vinson C, Rueger JM, Karsenty G (2000) Leptin inhibits
123
