General characteristics of the participants
The mean (± SD) age of the normal weight group was 59.01 ± 0.42 years, which was not statistically different from the mean age of the underweight group (61.43 ± 3.00 years) but was significantly different from that of the obese group (60.98 ± 0.44 years) (p = 0.001). Among body composition items, mean height was not different among the three groups; however, weight, BMI, and waist circumference were different from the normal weight group. The mean weight of the normal, underweight, and obese groups was 53.62 ± 0.21 kg, 41.43 ± 1.05 kg, and 64.65 ± 0.28 kg, respectively; the differences were statistically significant (underweight, p < 0.001; obese, p < 0.001). The mean BMI of the normal, underweight, and obese groups was 22.49 ± 0.06 kg/m2, 17.55 ± 0.20 kg/m2, and 27.31 ± 0.09 kg/m2, respectively (underweight group, p < 0.001; obese group, p < 0.001). The mean waist circumferences of the normal, underweight, and obese groups were 76.96 ± 0.29 cm, 65.30 ± 0.86 cm, and 89.47 ± 0.37 cm, respectively, which was significantly different from the normal weight group (underweight group, p < 0.001; obese, p < 0.001). The average age at menopause was not different among the groups (normal weight, 48.59 ± 0.22 years; underweight, 45.61 ± 1.66 years; obese, 48.48 ± 0.26 years). The average weight-corrected appendicular skeletal muscle mass was 34.29 ± 0.37 for normal weight group, 49.43 ± 3.35 for underweight group, and 28.52 ± 0.33 for the obese group, with the underweight group and the obese group showing statistically significant difference compared to the normal weight group (each p < 0.001). In case of bone density (g/cm2), the average bone density of the femoral neck (0.79 ± 0.03) and the entire femur (0.94 ± 0.03) in the underweight group was significantly higher than that of the normal weight group (femoral neck average, 0.73 ± 0.01; femur average 0.88 ± 0.01) (each p = 0.035, p = 0.029) In the case of T-score, only the average T-score of the femoral neck in the underweight group (-0.35 ± 0.24) was significantly different from that of the normal weight group (-0.87 ± 0.06) (p = 0.032). Regarding fragility fracture rate, there were differences among the three groups: underweight, 5.9% ± 2.9; normal, 1.1 ± 0.3%; and obese, 3.0 ± 0.7% (p = 0.001). In the smoking status, there was a difference in the proportion of non-smoker, former smoker and current smoker in the three groups(p=0.043, χ2=11.863). There were no statistical differences in treatment history and family history of osteoporosis, history of rheumatoid arthritis, drinking status, and moderate exercise among the three groups (Table 1).
Table 1. Characteristics for postmenopausal women according to BMI
|
Underweight
|
Normal
|
Obesity
|
p-value
|
|
(BMI <18.5)
N=45
|
(BMI ≥18.5 and <25)
N=1234
|
(BMI ≥25)
N=835
|
(𝟀2)
|
Est. number (n) (%)
|
105855 (2.1%)
|
3030556 (60.6%)
|
1867253 (37.3%)
|
|
Age (years)
|
61.43±3.00
|
59.01±0.42
|
60.98±0.44b
|
|
Height (cm)
|
153.36±1.61
|
154.28±0.22
|
153.77±0.28
|
|
Weight (kg)
|
41.43±1.05c
|
53.62±0.21
|
64.65±0.28c
|
|
BMI (kg/㎡)
|
17.55±0.20c
|
22.49±0.06
|
27.31±0.09c
|
|
Waist circumference (cm)
|
65.30±0.86c
|
76.96±0.29
|
89.47±0.37c
|
|
Menopausal age (years)
|
45.61±1.66
|
48.59±0.22
|
48.48±0.26
|
|
Weight-adjusted ASM
|
49.43±3.35c
|
34.29±0.37
|
28.52±0.33c
|
|
BMD (g/cm2)
|
|
|
|
|
Lumbar spine total
|
0.92±0.03
|
0.90±0.01
|
0.91±0.01
|
|
Femur neck
|
0.79±0.03a
|
0.73±0.01
|
0.72±0.01
|
|
Femur total
|
0.94±0.03a
|
0.88±0.01
|
0.88±0.01
|
|
BMD (T-score)
|
|
|
|
|
Lumbar spine total
|
-0.80±0.22
|
-0.91±0.06
|
-0.88±0.06
|
|
Femur neck
|
-0.35±0.24a
|
-0.87±0.06
|
-0.89±0.06
|
|
Femur total
|
0.31±0.18
|
-0.03±0.05
|
-0.07±0.06
|
|
Fragility fracture (%)
|
5.9(±2.9)
|
1.1(±0.3)
|
3.0(±0.7)
|
0.001 (11.186)
|
Treatment of OP (%)
|
|
|
|
0.369
|
None
|
91.8(±3.6)
|
91.4(±1.0)
|
93.2(±1.1)
|
(1.938)
|
Current treatment
|
8.2(±3.6)
|
8.6(±1.0)
|
6.8(±1.1)
|
|
FHx of osteoporosis (%)
|
|
|
|
0.540
|
No
|
78.3(±8.0)
|
85.1(±1.3)
|
86.0(±1.6)
|
(1.859)
|
Yes
|
21.7(±8.0)
|
14.9(±1.3)
|
14.0(±1.6)
|
|
Rheumatoid arthritis (%)
|
|
|
|
0.156
|
No
|
94.0(±3.7)
|
96.3(±0.6)
|
94.3(±0.9)
|
(3.835)
|
Yes
|
6.0(±3.7)
|
3.7(±0.6)
|
5.7(±0.9)
|
|
Smoking status (%)
|
|
|
|
0.043
|
Non-smoker
|
76.7(±7.8)
|
90.4(±1.0)
|
91.8(±1.1)
|
(11.863)
|
Former smoker
|
9.6(±5.0)
|
5.2(±0.7)
|
3.8(±0.7)
|
|
Current smoker
|
13.7(±6.6)
|
4.4(±0.7)
|
4.4(±0.9)
|
|
Alcohol consumption (%)
|
|
|
|
0.242
|
Non-drinker
|
65.4(±9.3)
|
52.4(±1.6)
|
49.1(±2.2)
|
(8.583)
|
Moderate drinker
|
23.9(±7.5)
|
40.4(±1.6)
|
44.6(±2.3)
|
|
Heavy drinker
|
10.8(±7.6)
|
7.2(±0.9)
|
6.3(±1.1)
|
|
Moderate exercise (%)
|
|
|
|
0.264
|
Yes
|
6.9(±4.1)
|
12.8(±1.3)
|
15.4(±1.9)
|
(3.855)
|
No
|
93.1(±4.1)
|
87.2(±1.3)
|
84.6(±1.9)
|
|
All values are weighted value and presented mean(±standard deviation) or percent(±standard deviation).
a, b and c are presented p-value <0.05, <0.01 and <0.001, respectively.
BMI, body mass index;ASM, appendicular skeletal muscle mass;BMD, bone mineral density;OP, osteoporosis;FHx, familial history.
Difference between vertebral and non-vertebral fracture rate according to BMI via Rao-Scott chi-squared test
The overall fragility fracture rates for the underweight, normal weight, and obese groups were 5.9%, 1.1%, and 3.0%, respectively, and the difference was statistically significant (p = 0.001, χ2 = 11.186). When fracture rates were compared between the vertebral and non-vertebral fracture rates, vertebral fracture rate for the underweight group (4.5 ± 2.6%) was significantly higher compared with the normal weight group (0.6 ± 0.2%) and obese group (0.9 ± 0.4%) (p = 0.014, χ2=7.644). In the case of non-vertebral fracture rate, that of the obese group (2.3 ± 0.6%) was relatively higher than that of the normal weight group (0.7 ± 0.3%) and underweight group (1.4 ± 1.4%), with a statistically significant difference among the three groups (p = 0.011, χ2 = 8.040) (Figure 2).
Odds ratio for fragility fracture according to multiple logistic regression analysis
The odds ratio for fragility fracture in the underweight and obese groups was compared with the normal weight group via multiple logistic regression analysis. In model 1, which was not corrected, the odds ratio for fracture in the underweight group was 5.48 (95% CI 1.66–17.76) and 2.72 (95% CI 1.38–5.37) in the obese group. In model 2, which was corrected for age and family history and treatment history of osteoporosis, odds ratio for the underweight group was 5.14 (95% CI 1.77–14.93) and 3.12 (95% CI 1.50–6.48) in the obese group. In model 3, which was corrected for age, family history and treatment history of osteoporosis, history of rheumatoid arthritis, smoking status, drinking status, and moderate exercise, the odds ratio for the underweight group was 5.48 (95% CI 1.80–16.73) and 3.33 (95% CI 1.61–6.87) for the obese group (Table 2).
Table 2. Odds ratio(OR) of fragility fracture for postmenopausal women by multivariate logistic regression analysis.
|
OR (95% CI)
|
|
|
Normal weight (BMI ≥18.5 and <25)
|
1 (Reference)
|
|
|
Underweight (BMI <18.5)
|
|
Model 1
|
5.48 (1.66-17.76)
|
Model 2
|
5.14 (1.77-14.93)
|
Model 3
|
5.48 (1.80-16.73)
|
|
|
Obesity (BMI ≥25)
|
|
Model 1
|
2.72 (1.38-5.37)
|
Model 2
|
3.12 (1.50-6.48)
|
Model 3
|
3.33 (1.61-6.87)
|
Model 1 : Crude
Model 2 : Adjusted for age, family history of OP and treatment of OP.
Model 3: Adjusted for age, family history of OP, treatment of OP, presence of rheumatoid arthritis, smoking status, alcohol consumption and moderate exercise.
BMI, body mass index;OP, osteoporosis.
Fragility fractures were classified as vertebral and non-vertebral fractures, and logistic regression analysis was performed after correcting for age, family history and treatment history of osteoporosis, history of rheumatoid arthritis, smoking status, drinking status, and moderate exercise. In the underweight group, the odds ratio for vertebral fracture was 5.49 (95% CI 1.31–23.09) times higher than that of the normal weight group. In the obese group, there was no statistically significant difference in the odds ratio for vertebral fracture, while the non-vertebral fracture odds ratio was observed to be 3.87 (95% CI 1.45–10.33) times higher. When non-vertebral fractures were compared after dividing them into hip and wrist, the obese group had an odds ratio for hip fracture 22.05 (95% CI 1.33–365.31) times higher and 3.85 (95% CI 1.35–10.93) times higher for wrist fracture (Table 3).
Table 3. Odds ratio(OR) of vertebral fracture(VF) and non-vertebral fracture(NVF) according to BMI.
|
VF
|
NVF
|
|
OR (95% CI)
|
OR (95% CI)
|
|
Total
|
Total
|
Hip
|
Wrist
|
Underweight
(BMI <18.5)
|
5.49 (1.31-23.09)
|
1.83 (0.22-15.60)
|
10.65 (0.38-295.97)
|
2.02 (0.24-17.29)
|
Normal
(BMI ≥18.5 and <25)
|
1 (Reference)
|
1 (Reference)
|
1 (Reference)
|
1 (Reference)
|
Obesity
(BMI ≥25)
|
1.89 (0.59-6.00)
|
3.87 (1.45-10.33)
|
22.05 (1.33-365.31)
|
3.85 (1.35-10.93)
|
Adjusting for age, family history of osteoporosis, treatment of osteoporosis, presence of rheumatoid arthritis, smoking status, alcohol consumption and moderate exercise.
BMI, body mass index