Introduction: Fat mass is associated with secretion of bone-active hormones from the pancreatic β-cell and secretion of bone-active factors from adipocytes;1 however, some studies have challenged that theory. In this study, we investigated whether obesity was related to osteoporosis in adults with normal BMIs.
Materials & methods: We retrospectively reviewed 1,345 consecutive men and postmenopausal women aged more than 50 years with normal BMIs who were referred from our health check-up center for dual-energy X-ray absorptiometry (DXA) scans. Each patient underwent a standard BMD scan of both hips and the lumbar spinal region (L1 to L4), and body fat (BF, %) was measured using DXA. Osteoporosis is when the BMD T-score is lower than - 2.5 SD below the mean among young women. Obesity is when total body fat exceeds 38% for women or 25% for men.2 Normal BMI is 18.5?24.0 kg/m2 in Taiwan.
Results: Among women with normal BMIs, obesity occurred 32.84% of the time. Results showed a significant negative correlation between %BF and whole-body BMD (r=-0.297, p<0.001) and between %BF and BMD in bilateral femoral necks (right, r=-0.73, p<0.01; left, r=-0.82, p<0.01) but not in the lumbar spine (r=0.032, p=0.20). Also, 30.16% had osteoporosis, 56.43% low bone mass, and 13.40% normal BMDs. No significant difference in %BF was found between these three groups (p=0.76). Among the men, obesity occurred 22.70% of the time. Results showed a significant negative correlation between %BF and whole-body BMD (r=-0.331, p<0.001) and between %BF and BMD in the left femoral neck (r=-0.059, p=0.05) but not in the lumbar spine (r=0.021, p=0.48) or right femoral neck (r=0.045, p=0.13). Also, 17.36% had osteoporosis, 60.77% low bone mass, and 21.87% normal BMDs. No significant difference in %BF was found between these three groups (p=0.30).
Discussions: Based on BMI-adjusted data, these findings agree with a recent study showing that obesity was not correlated with body-weight adjusted bone loss or osteoporosis.3 They differ from reported positive correlation changes in BMD and body fat measured by DXA.4 The spurious decrease in BMD could be attributable to spurious increases in both BMC (numerator) and bone area (denominator for BMD) from artifacts in DXA.4
Conclusion: Obese and non-obese individuals have similar degrees of osteoporosis among older adults with normal BMIs.
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