1 Division of International Public Health Nutrition, Institute of Health Biosciences, University of Tokushima Graduate School, Tokushima, Japan
2 Vietnam National Institute of Nutrition, Hanoi, Vietnam
3 Nutrition Center of Ho Chi Minh City, Ho Chi Minh City, Vietnam
Reprint requests to Dr. Shigeru Yamamoto, Division of International Public Health Nutrition, Institute of Health Biosciences, University of Tokushima Graduate School, 3 Kuramoto, Tokushima, 770-8503 Japan (e-mail: syamamoto{at}nutr.med.tokoshima-u.ac.jp).
Received for publication June 30, 2004. Accepted for publication December 6, 2004.
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ABSTRACT |
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cross-sectional studies; osteoporosis; risk factors; ultrasonics; Vietnam
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INTRODUCTION |
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The optimal method for diagnosing osteoporosis is to measure bone mineral density by dual-energy x-ray absorptiometry at the hip and lumbar spine (5). However, it is very difficult to apply this procedure in community-based studies because of its lack of portability and its cost. Furthermore, the procedure exposes subjects to low, but significant doses of ionizing radiation. Quantitative ultrasound (QUS) measurement, a technique for measuring the peripheral skeleton, has been proposed because it can be performed quickly, is relatively inexpensive, is portable, and involves less radiation. Thus, QUS could be an ideal tool to screen for osteoporosis at the community level (6
12
).
Although Asians are thought to have lower bone mass than Caucasians because of their smaller body size (13), few population-based studies have been conducted in Asian countries. In Vietnam, life expectancy is increasing as the economy improves (14
), and, with a longer lifespan, there is concern about an increased prevalence of osteoporosis. However, the prevalence of osteoporosis and its related factors remains unclear. A pilot study in 2000 measuring the bone mass of Vietnamese adult men and women living in Hanoi City estimated that bone density is low in this population (15
). However, data were insufficient to characterize the prevalence. Thus, further studies on the epidemiologic distribution of osteoporosis and associated factors in Vietnam are required. Although osteoporosis can affect both men and women of any age, women are four times more likely than men to develop osteoporosis (16
). Thus, the aim of the present study was to determine the prevalence of osteoporosis and related factors in Vietnamese adult women.
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MATERIALS AND METHODS |
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Hanoi City is the capital of Vietnam, located in the northern area of the country, and has a population of approximately 3 million inhabitants (17). There are 228 wards and communes divided into 102 urban wards and 126 rural communes. A multistage sampling method was used to select subjects. First, 30 of the total 228 wards and communes were chosen by using a probability proportional-to-size sampling method (18
). From each of the selected wards and communes, 80 women aged 20 years or older were chosen randomly and were stratified by 5-year age groups (2024, 2529, 3034, 3539, 4044, 4549, 5054, 5559, 6064, 6569, 7074, 7579, 8084, and
85 years). To recruit subjects, a list of all families that included women aged 20 years or older was constructed, and family codes were created. From this list, the first family was selected by randomly choosing a family code. In each family selected, all women aged 20 years or older and free of bone deformities and acute illnesses were invited to participate. After selecting the first family, we used the "random walking" method to approach other families, adding subjects to obtain 80 women stratified by 5-year age groups (18
). From 30 selected wards and communes, 2,400 women were selected to participate.
This survey was carried out at the local health centers of the selected sites. To maximize participation, the local health staff visited each household to explain the study, obtain written consent from each subject, and remind participants of the time and date of the survey. At the end of the survey, a total of 2,368 participants had been included.
Interview
All participants completed a structured questionnaire. Included was an assessment of subjects' medical history, particularly focusing on hyperparathyroidism, gastrectomy, diseases of the kidney, diabetes mellitus, rheumatoid arthritis, chronic liver disease, chronic malabsorptive syndromes, cancer, and jejunoileal bypass, as well as current or past treatment with glucocorticoids and/or thyroid hormone. Subjects were excluded from analysis if they had at least one of the above conditions. Use of oral contraceptive pills was also recorded.
Information on fracture history, family history of fracture and osteoporosis, socioeconomic status, lifelong occupation, educational level, and recreational weight-bearing exercise was collected from each subject. The interview also asked about current age and age at menarche and menopause, as well as number of children.
Lifelong occupation was defined as the occupation that the subject engaged in most frequently in her life. It was classified as heavy work (farmers, manual workers), office work (office clerks and other sedentary jobs), or domestic work (housewife). Educational level was categorized in three groups, by number of years of schooling: low level (5 years), medium level (68 years), and high level (
9 years). Recreational weight-bearing exercise was assessed by inquiring about regular weight-bearing exercise during at least the past 12 months. The subjects reported the number of sessions of weight-bearing exercise of at least 30 minutes per week. Active behavior was defined as engaging in more than two sessions per week.
Anthropometry measurement
Height and weight were measured while subjects were standing, wearing light clothing and no shoes. Body mass index was calculated as the ratio of weight (in kilograms) to height (in meters) squared. Waist circumference was measured at the minimum circumference between the umbilicus and iliac crest, and hip circumference was measured at the widest circumference around the buttocks.
Bone mass assessment
Bone mass was assessed by speed of sound (m/second) using a QUS device (CM-100; ELK Corporation, Tokyo, Japan). This device is small and portable, with a gel-coupled (dry) system that can measure speed of sound at the calcaneus. Coefficients of variation for the device were measured short term in vivo and in vitro. Precision error (percent coefficient of variation) using the phantom technique was 0.15 percent and, in vivo, was 0.27 percent (19).
For all subjects, speed of sound was measured at the right calcaneus. The measurement was taken in a temperature-controlled environment and was performed by a trained medical technician only. Standardization and calibration with standards were performed before the first measurement of each survey day.
The T-score for each subject was calculated by using the peak speed-of-sound value for a defined population of young adults, and its standard deviation, with the following equation (20): T-score = speed of soundsubject speed of soundpeak value for young adults/standard deviationpeak value for young adults.
We calculated the peak speed-of-sound value for young adults (speed of soundpeak value for young adults) by estimating peak bone mass, which was itself defined as the average maximum bone mass achieved by young, healthy, sex- and race-matched adults (21). For our own population, we defined the young adult population by identifying the age range at which speed of sound reached peak value. Speed of soundpeak value for young adults and standard deviationpeak value for young adults were determined as the mean speed-of-sound value for the young adult population and its standard deviation, respectively.
A person was classified as having osteoporosis if her T-score was 1.8 and as normal if the score was >1.8.
Statistical analysis
In this paper, data are presented as percentage and as mean (standard deviation). Student's t test (two sided) was applied to examine differences in age, number of children, anthropometric indicators, and speed-of-sound values between women in rural and urban areas. Bonferroni's t test was used to identify significant differences in speed-of-sound values for 5-year age groups to define the age range for young adults and their peak speed-of-sound value. Chi-square testing was used to examine differences in the prevalence of osteoporosis, active weight-bearing exercise, lowest educational level, and heavy lifelong occupation between women in the rural and urban areas.
Multiple logistic regression analysis was used to test several models for the associations between osteoporosis assessed by speed of sound and other variables. Here, data are presented as odds ratios and 95 percent confidence intervals. Associations were considered statistically significant at the p < 0.05 level.
All statistical procedures were performed by using SPSS software for Windows, version 10.0 (SPSS, Inc., Chicago, Illinois).
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RESULTS |
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Table 1 shows the characteristics of subjects; their mean age was 48.5 (standard deviation, 16.5) years. In the rural areas, anthropometric indicators such as weight, body mass index, and waist/hip ratio were significantly lower in both premenopausal and postmenopausal women, while height was significantly lower only in postmenopausal women compared with those in the urban areas.
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Prevalence of osteoporosis
Speed-of-sound value reached its peak at age 3034 years, started to decline at age 3539 years, and declined significantly from age 45 to 49 years. Because mean speed-of-sound values at ages 3539 years and at ages 4044 years were similar or even higher than for the age group 2024 years, we defined women aged 2044 years as young adults to calculate peak speed-of-sound value (speed of soundpeak value for young adults) and its standard deviation (standard deviationpeak value for young adults) for our own population. The peak speed-of-sound value for the young adults was determined to be 1,536 (standard deviation, 30) m/second. On the basis of this value, the crude prevalence of osteoporosis was estimated at 15.4 percent in the study population. Table 2 shows that the prevalence of osteoporosis in the age groups increased with age (2 = 669.7; p < 0.001, two-sided). After we adjusted for age (using 1999 Hanoi census data), the estimated prevalence of osteoporosis was 9.0 percent.
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DISCUSSION |
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Speed-of-sound measurements at the calcaneus can identify persons at risk of osteoporotic fracture as reliably as bone mineral density measurements (2326
) and could be an ideal tool to screen for osteoporosis at the community level (6
12
). However, it also has been demonstrated that the T-score threshold of 2.5 may lead to underestimation of the prevalence of osteoporosis when QUS is measured at the heel (21
). Recent studies on the Hologic Sahara and the Hologic UBA575+ (Hologic, Bedford, Massachusetts) and on the Osteometer DTUone (Osteometer MediTech, Inc., Hawthorne, California) QUS devices indicate that a T-score threshold of 1.8 identifies the same percentage of persons with osteoporosis as the World Health Organization threshold for bone mineral density measurements (27
). The CM-100 device used in our study is very similar to the Sahara device and is also used to measure QUS parameters at the calcaneus. The device comes with a manufacturer's recommended cutoff value for diagnosing osteoporosis, validated by dual-energy x-ray absorptiometry (28
). In addition, we found excellent agreement between the manufacturer's cutoff and our data-derived T-score in classifying osteoporosis (kappa = 0.967, p < 0.001). Therefore, we felt it was reasonable to apply a T-score threshold of 1.8 to define osteoporosis in our population.
The age at peak bone mass depends on skeletal sites or technologies used (20). Evidence from previous studies indicates that QUS parameters start to decline from the age of 4045 years and fall steadily thereafter (29
, 30
). Our study showed similar results, with the peak value of speed of sound occurring from 20 to 44 years of age, followed by a significant decline thereafter. For these reasons, we concluded that defining peak speed-of-sound value as the mean for women aged 2044 years and defining osteoporosis by using a T-score threshold of 1.8 is reasonable in screening for osteoporosis in our population when the CM-100 device is used.
In this study, the prevalence of osteoporosis in Vietnamese women was found to be lower than that in Japanese women in the age group 5079 years (29.5 percent vs. 51.2 percent) (31) but was similar or higher in comparison to nearby countries such as China (3.7 percent vs. 3.7 percent in the age group 4049 years, 8.4 percent vs. 3.9 percent in the age group 5059 years) (32
) and Korea (12.8 percent vs. 11.8 percent in women aged
50 years) (33
) when the same age range was compared or when the same method was used to classify osteoporosis. When we put the information into context, Japanese women aged 5079 years were infants and young children during World War II. Their nutrition was poor, and calcium intake in 1946 was only 253 mg per day (34
). Therefore, the prevalence of osteoporosis in that age group is very high. In Vietnam, women who are aged 5079 years were also exposed to war and had poor nutrition. Thus, it is reasonable to compare the prevalence of osteoporosis between Vietnamese and Japanese women aged 5079 years. The Vietnamese women aged 4049 years were born when the war had just ended. The situation may be the same with Chinese women in the same age range. This factor might explain why the prevalence of osteoporosis is comparable in Vietnamese and Chinese women aged 4049 years. When classified on the basis of the T-score threshold of the World Health Organization, the prevalence of low bone mass among Vietnamese women aged 20 years or older in 2003 increased compared with that in 2000 (6.4 percent vs. 5.7 percent) (15
). These comparisons may be slightly weakened by the difference in the measurement, calibration, and standardization methods used in these studies, but our findings indicate that osteoporosis is becoming a noteworthy problem in Vietnam.
Factors affecting bone mineral density have been studied extensively (3538
). Recently, the impact of risk factors on QUS parameters has also been given more attention. Our data show that increasing age and postmenopausal status are predictors of low speed of sound. Increased age was associated with a significantly increased risk of osteoporosis, especially when women become postmenopausal. This finding is consistent with those from other studies (10
, 15
, 39
). Our study also agreed with previous research reporting that low educational level was related to increased risk of osteoporosis (40
). Low stature and a large number of children are predictors of low speed of sound. These associations were demonstrated in previous studies (41
43
) and were also confirmed in our data. In addition, our survey indicates that engaging in recreational, active weight-bearing exercise and having a lifelong occupation involving heavy work can help protect subjects from osteoporosis.
Our study also revealed contrasting distributions of osteoporosis between urban and rural areas of the country. To our knowledge, this finding has not been observed in other countries and is likely due to socioeconomic characteristics of Vietnamese. In rural areas, most of the people are farmers and take part in more active weight-bearing exercise, which might explain why the prevalence of osteoporosis among rural premenopausal women was lower compared with that among urban women. However, because rural postmenopausal women have more children, a lower stature, and a lower educational level, the prevalence of osteoporosis among postmenopausal women in the rural areas was higher. In addition, rural women consume fewer dairy products, and eggs/milk consumption in the rural areas was lower than in the urban areas (5.4 g per capita/day vs. 25.5 g per capita/day). Moreover, the postmenopausal women experienced greater problems with access to enough food, including calcium-rich foods, when they were teens and young adults because of war and the early years thereafter (44). Exposed to a long period of inadequate calcium intake, rural postmenopausal women are more likely to suffer from osteoporosis. This finding may partially explain why the prevalence of osteoporosis among postmenopausal women was higher in the rural areas, and it should be confirmed by further studies in order to design an appropriate intervention strategy.
The present study has several limitations. First, the T-score threshold for diagnosing osteoporosis by QUS or use of the CM-100 device has not been established. However, in the context of epidemiologic studies at the community level in developing countries, we could only apply QUS and use a T-score threshold of 1.8 to identify subjects with osteoporosis. Many studies support the view of using QUS to screen for osteoporosis at the community level (6
12
). A previous study also applied a T-score threshold of
1.8 to define osteoporosis using QUS (45
). For these reasons, we believe that, with a large sample size and random sampling methods, our data may truly represent the prevalence of osteoporosis in Hanoi City, or they may even underestimate its prevalence. Second, this study was a cross-sectional survey, and we could not measure all factors affecting the risk of osteoporosis. Moreover, using a prevalence measure to assess risk factors also has limitations because the factors associated with osteoporosis may not reflect the real cause-effect relation. Risk factors assessed by using prevalence measures can only suggest the hypothesis for a possible cause-effect relation. Thus, a prospective study is needed to confirm any association between low speed of sound and risk factors and to explain the differing patterns of osteoporosis distribution between urban and rural areas.
In conclusion, this study shows that the prevalence of osteoporosis in Vietnamese adult women in Hanoi City, determined by QUS, is relatively high compared with that in nearby countries. In addition, our data indicate differing distributions of osteoporosis between rural and urban areas of Hanoi City. These findings suggest that osteoporosis is a problem in Vietnam. Furthermore, using multiple logistic regression, we assessed associations between low speed of sound and risk factors, as well as protective factors. Because osteoporosis is related to considerable mortality and increasingly higher costs of health care, screening for osteoporosis, particularly in high-risk populations, and setting up a national program to prevent and control osteoporosis in Vietnam are urgently needed.
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References |
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