In this present cohort study, we were able to calculate mean BMD and bone turnover markers by age and sex for the elderly aged 50 years and older according to the Japanese population ratio in more than 400 subjects randomly selected from a rural town registry in Japan. We were able to create a cohort that more accurately reflects the general population in comparison to traditional population studies that recruit active volunteers. Another feature of this study was the uniform distribution of age and gender ratios between 50 and 89 years old, as a result of collecting about 50 physical examination participants by age and gender. This uniform distribution is advantageous for making accurate statistical comparisons between men and women and between age groups.
In this study, the BMD decreased with age in the femoral neck and total hip in males and females. The BMD of the femoral neck, total hip, and lumber spine were comparable with previous studies in our country and elsewhere after accounting for gender and age (Table 7). Previous studies have demonstrated that BMD decreased with aging [13, 14], and this study obtained the same results as have been described in the literature.
Table 7
Mean BMD values in previous reports
Study | Country | Sex | Number | Age(years) | Femoral neck | Total hip | Lumber spine |
Lee, 2019 | Korea | Male | 244 | age > 65 | 0.78 (0.007) | 0.87 (0.008) | 0.94 (0.005) |
| | Female | 319 | | 0.56 (0.005) | 0.70 (0.005) | 0.73 (0.008) |
Schacht, 2019 | Denmark | Male | 98 | 69.0 (6.0) | 0.95 (0.18) | 1.10 (0.24) | 1.31 (0.26) |
| | Female | 86 | 70.0 (5.8) | 0.83 (0.19) | 0.88 (0.24) | 1.13 (0.25) |
Fuggle, 2018 | England and Wales | Male | 194 | 64.4 (2.5) | 1.03 (0.14) | | 1.06 (0.15) |
| | Female | 171 | 66.5 (2.7) | 0.89 (0.13) | | 0.95 (0.17) |
Fujiwara, 2003 | Japan | Male | 763 | 62.9 (9.8) | 0.73 (0.11) | | 0.98 (0.16) |
| | Female | 1593 | 65.4 (9.8) | 0.62 (0.11) | | 0.82 (0.11) |
Our study | Japan | Male | 203 | 69.5 (11.2) | 0.88 (0.13) | 0.95 (0.15) | 1.27 (0.25) |
| | Female | 208 | 70.0 (11.0) | 0.74 (0.11) | 0.81 (0.13) | 1.04 (0.19) |
Values represent mean (standard deviation). |
All bone markers in this study were within the standard value for males and females in each generation [5, 7]. In men and women, pentosidine and DPD increased with age. TRACP-5b increased with age in males. However, other markers showed no association with age. In this study, subjects were randomly selected from a rural Japanese town; thus, subjects may be healthy. Aging may exert little influence on bone markers, while the prevalence of osteoporosis and osteopenia increased with aging in both males and females.
In terms of the association between low BMD and bone markers, there was a significant association between low BMD and TRACP-5b in females. TRACP-5b is a bone resorption marker that is not affected by renal dysfunction and has a low diurnal variability [15, 16]. Thus, TRACP-5b has been considered a useful marker. TRACP-5b was inversely correlated with BMD in females [17]. Furthermore, TRACP-5b has been described to be associated with increased fracture risk in elderly females [18, 19]. TRACP-5b could be a potential marker to predict fractures. In this study, TRACP-5b was related to low BMD in randomly selected female residents in the area. High bone resorption may be a factor for low BMD in female residents. TRACP-5b may be marker which was useful for the detection of low BMD.
There is a limitation in this study. Although the research design reduces the sampling bias by adopting random sampling from the resident register, we may not have been able to control for all potential biases as a result of the low participation rate.