Background
Osteoporosis is a bone disease that can reduce both bone mass and bone strength. It is typically thought to be age-related
Methods
Study Population
The present study included 965 patients, who were older than 20 years old, chronic schizophrenia admitted to the Psychiatric Department of Yuli Veterans Hospital in Taiwan, ROC, between 2003 and 2004. All of these patients met the DSM-IV criteria for schizophrenia as diagnosed by psychiatrists in Yuli Veterans Hospital. Patients with severe extra-pyramidal symptoms (EPS), poor disease control, or severe debility that precluded cooperation with the bone density survey were excluded from the study. For comparison, 405 community members, who were older than 20 years old, living in the same district as Yuli Veterans Hospital, also entered the study. All residents who lived in this district were visited at their home. Those who were not living in Yuli Town during the survey period or did not give consent or had medical or mental disability that prevented them from completing the examination were excluded. The study was approved by the medical ethics policy of the Institutional Review Board Committee at Yuli Veterans Hospital (serial No. 92-11-02A).
Bone Mass and Quantitative Ultrasound
A QUS-II Calcaneal Ultrasonometer (Metra Biosystems, Mountain View, CA, USA) was used to measure bone density as broadband ultrasound attenuation (BUA) data. Ultrasound bone densiometry is reported to correlate well with the results of DXA and can predict osteoporosis-related fracture
Osteoporosis is defined by decreased bone mineral density (BMD) to a level of or less than -2.5 SD of the mean value of young adults. Firstly, our group assessed the precision of the quantitative ultrasound densitometry. Intra-test precision was calculated from three repeated scans with repositioning in 25 volunteers; the short-term coefficient of variation was 3.5% for BUA. T-scores used in our data were calculated from measured BUA data, the apparatus' specific threshold and further adjustment using data from Chinese patients living in Taiwan as reported by N.P. Yang
Statistical Analysis
All subjects were classified into two subject groups. Admitted schizophrenic patients were classified as schizophrenic patient group. Residents lived in the community were classified as community population group. All the subjects were classified into 5 age groups in decades of age from 20 to 60 years old and 60 years above. Correlation between measured BUA value and weight, gender, subject groups, and age groups was tested by fractional factorial generalized linear model. Interactions between age groups and subject groups were also tested in the same model. Effects of weight, gender and age groups on the differences of means of measured BUA value was tested with generalized linear model in each subject group. Trends of mean BUA values between age groups stratified by subject groups and gender was tested by nonparametric test for trend. Prevalence of osteoporosis data were stratified by both gender and age groups for both groups and reported by descriptive analysis and was compared further with the prevalence reported in Taiwan. All statistical calculations were conducted using the Stata 10/SE system for Mac.
Results
The demographic data and BUA value results stratified by subject groups, age groups and gender are presented in Table
The Basic Characteristics of the Schizophrenic Patients compared to community population, sampled from the same community, Yu-Li area, Taiwan
Age Strata (y/o)
- Studied Subjects
- BUA (dB/MHz)
- Weight (Kgw)
Schizophrenic
Community
Schizophrenic
Community
Schizophrenic
Community
No.(%)
No.(%)
Mean (S.D.)
Mean (S.D.)
Mean (S.D.)
Mean (S.D.)
Male
20–29
59(9.5)
12(6.6)
77.1(15.3)
86.1(21.6)
69.3(13.9)
63.9(8.9)
30–39
184(29.5)
18(9.8)
82.3(17.0)
90.1(17.2)
71.3(19.2)
71.3(10.5)
40–49
177(28.4)
30(16.4)
83.9(18.6)
92.0(19.4)
67.2(15.3)
69.5(10.9)
50–59
77(12.4)
28(15.3)
80.3(18.2)
83.7(20.7)
67.4(13.4)
67.3(8.3)
60 or more
126(20.2)
95(51.9)
82.2(18.2)
78.0(21.1)
52.9(9.2)
66.8(10.9)
Total
623
183
Female
20–29
22(6.4)
16(7.2)
71.9(26.5)
85.3(11.1)
69.6(12.3)
53.7(7.7)
30–39
84(24.6)
33(14.9)
76.9(20.8)
85.8(11.7)
70.2(15.6)
57.3(9.9)
40–49
97(28.4)
38(17.1)
81.2(20.5)
86.3(16.9)
71.9(19.1)
59.8(10.7)
50–59
97(28.4)
45(20.3)
82.3(20.1)
72.0(16.5)
68.4(7.8)
58.0(9.2)
60 or more
42(12.3)
90(40.5)
79.0(19.9)
68.7(17.1)
65.3(6.2)
57.5(10.2)
Total
342
222
Totally
965
405
Mean BUA values were lower for male schizophrenic patients as compared with male community population group of same age groups if they were 60 years old or younger. But mean BUA value was higher for male schizophrenic patients in the age group older than 60 years. Mean BUA values were also lower for female schizophrenic patients as compared with female community population group of same age groups if they were younger than 50 years old. But mean BUA values for female schizophrenic patients were higher in age groups older than 50 years. This is demonstrated in Fig.
BUA vs. age with 95% confidence and fit line by subject population and sex
BUA vs. age with 95% confidence and fit line by subject population and sex.
The male schizophrenic patient group has a higher mean weight than the male community population group except in the age group 40–50 and the age group > 60 years old. The mean weight of the female schizophrenic patient group is higher than the female community population group across all age groups.
Table
Comparison of BUA in schizophrenic patient and community population group stratified by age group, gender by fractional factorial generalized linear model
(dependent variable = BUA)
Independent variables
coef.
std. err.
p-value
Gender (female vs. male)
-4.251
1.054
***
Weight (kgw)
0.158
0.036
***
Group#(community vs. schizophrenic)
13.069
4.096
**
Age group 20–39
-23.949
6.497
***
Age group 30–39
-15.424
4.980
**
Age group 40–49
-10.727
4.777
*
Age group 50–59
-----
-----
n.s.
Age group ≧ 60
-----
-----
n.s.
Group*Age group 20–39
-----
-----
n.s.
Group*Age group 30–39
-----
-----
n.s.
Group*Age group 40–49
-----
-----
n.s.
Group*Age group 50–59
-16.723
4.826
**
Group*Age group ≧ 60
-20.967
4.563
***
Constant
80.987
4.741
***
n.s. : not significant
* : p < 0.05
** : p < 0.01
*** : p < 0.001
#: schizophrenic patient group and community population group
Generalized linear model was used to test the effect of gender, weight, and age on the difference of mean BUA value and was stratified by subject groups. The result is shown in Table
Comparison of BUA by gender, weight, and age in schizophrenic patient and community population group with generalized linear model
Schizophrenic patient
Community population
Independent variable
β
std. err.
p-value
β
std. err.
p-value
Gender (male vs female)
-2.731
1.278
*
-4.474
1.986
*
Weight (kgw)
0.105
0.041
*
0.445
0.086
***
Age (years)
0.097
0.044
*
-0.362
0.052
***
Constant
73.189
4.218
***
78.992
8.206
***
* : p<0.05
** : p<0.01
*** : p<0.001
Table
Comparison of low bone mass condition between the comminuty population and a schizophrenic population in Taiwanese
- prevalence of low bone mass [t < 1.0]
- prevalence of severe low bone mass [t ≦ -2.5]
Schizophrenic population in Yuli area
Community population in Yuli area
Community-surveyed People in Kinmen, Taiwan, 2000–2003§
Schizophrenic population in Yuli area
Community people in Yuli area
Community-surveyed People in Kinmen, Taiwan, 2000–2003§
(%)
(%)
(%)
(%)
(%)
(%)
Age Strata
Male
20–29 y/o
54.2
50.0
-----
15.3
0
-----
30–39 y/o
42.9
33.3
-----
9.8
0
-----
40–49 y/o
37.3
33.3
35.5
6.8
3.3
3.9
50–59 y/o
46.8
50.0
42.5
13.0
10.7
7.1
> 60 y/o
48.4
55.8
55.8
6.4
25.3
16.9
Female
20–29 y/o
77.3
18.8
-----
50.0
0
-----
30–39 y/o
50.0
18.2
-----
26.2
0
-----
40–49 y/o
42.3
31.6
38.4
17.5
5.3
6.7
50–59 y/o
46.4
68.9
52.9
14.4
28.9
16.5
> 60 y/o
52.4
78.9
84.1
19.1
31.1
50.9
Note: The above three population were screened for low bone mass using the same ultrasonography, QUS-II. The t-score was calculated using machine BUA value and adjusted as: (BUAindividual – 92.72)/13.36 for the male, and (BUAindividual – 87.90)/10.68 for the female. Those were based on the published reference§.
§Nan-Ping Yang, Shao-Yuan Chuang, Shui-Hu Chen, Pesus Chou. Screening for low bone mass with quantitative ultrasonography in a community without dual X-ray absorptiometry: population-based study. BMC Musculoskeletal Disorders 2006;7:24.
Discussion
The results of our study reveal lower BUA value in the schizophrenic patient group while these patients are young. The prevalence of low bone mass and severe low bone mass showed similar changes when compared with community populations from the same geographical area and from Kinmen Island, which is in a different geographical location. The geography- related effect can be ruled out in this study. Yuli town is in a rural area in the east part of Taiwan. Healthier young people move to the cities for work. For this reason, the sample size of the 20–29 and the 30–39 year old group is small in the community population group. This is also the reason of higher osteoporosis prevalence in the 20–29 year-old male group.
Poorer bone mass in psychiatric patients has been reported in many literatures
A rapid decrease of bone mass and an increase of osteoporosis during the menopausal transition are reported in the community female population
The BUA value keeps relatively stable while aging, as shown in trend analysis. In the generalized linear model, BUA increased significantly with age increase. Aging is not a risk factor of poor bone mass in schizophrenic patient group in our study, and is a protective factor as the statistical result. Aging has been reported to be a risk factor of osteopenia in psychiatric patients treated with prolactin-elevating antipsychotics.
The chronic schizophrenic patient may also have several of the risk factors for osteoporosis-related fractures, commonly including unsteady gait, decreased physical activity and the use of sedative medications and low cognitive function. Residents of a long-term care unit are at a higher risk of osteoporotic fractures due to one or more of following risk factors: advanced age, poor physical function, low muscle strength, decreased cognition, dementia, poor nutrition and the use of certain medications.
Conclusion
In this study, schizophrenic patients have lower BUA values since they are young when compared with the community population. Aging and menopausal transition effect on bone mass in the general female population cannot be seen in the schizophrenic patient group. The bone mass distribution of schizophrenic patients is different from that of the community population. This is a cross-sectional study, and does not include the information of sex hormone, bone metabolism related hormones, the type of antipsychotic medication used and bone turnover markers is its limitation. Use of ultrasonographic assessments instead of DXA scans and the assessment of bone mass at only one location is another limitation of this survey. Further studies are necessary to clarify the hormonal changes, bony metabolism and effects of medication on bone mass characteristics in schizophrenic patients. Prospective study begins from the onset of schizophrenia may be also necessary. Once the cause and effect relationships are clearer, intervention may be used to either prevent or delay the onset of osteoporosis in these patients.
Competing interests
The whole study is funded by research budget of Yuli Veterans Hospital for supporting and encouraging staff to perform study related to medicine. Otherwise, there are no other competing interests.
Authors' contributions
JHR conducted and performed the whole project. NPY carried the data analysis. CMC and CYL confirmed the schizophrenia diagnosis. THL sampled the schizophrenic patients within all inpatient in Yuli Veterans Hospital and arranged and recorded result and arranged the schedule of ultrasound densitometer. PC designed and supervised the whole project.