Associations of Bone Mineral Density With Blood Pressure and Obesity in Hong Kong Chinese Adults

Background: There were conflicting results regarding the association between blood pressure (BP) and bone mineral density (BMD) in previous studies. Obesity, often co-existing with high BP, may explain the discrepancy in those findings. The aim of this study was to examine the association between BP and BMD in Hong Kong Chinese adults, and to determine whether the relationship between BP and BMD differed in subjects with and without obesity. Methods: Eight hundred and one adults aged from 45 to 86 years were recruited at two outpatient clinics in Hong Kong. Data of weight, height, waist circumference, BP, disease diagnosis were extracted from medical records at the clinics. The femur neck total BMD (g/cm2) was measured by dual-energy X-ray absorptiometry (DXA). The demographics, smoking, drinking, and other covariates were collected by a self-administered questionnaire. Osteoporosis, osteopenia, and normal bone mass were classified by BMD T-score for analysis. Results: The average systolic BP was 121.5 mmHg, 123.2 mmHg, and 126.9 mmHg, diastolic BP was 71.9 mmHg, 72.6 mmHg, and 75.8 mmHg among osteoporosis, osteopenia, and normal bone mass groups, respectively. Subjects with osteoporosis had lowest BP level (all P<0.01). In the multiple liner regression analysis, after adjustment of age, gender, BMI, cancer, diabetes, and chronic renal failure, higher systolic BP was associated with higher BMD (B=0.00078, 95%CI: 0.00020 to 0.00136, P<0.01). This association was significant in both males and females (both P<0.05). No significant association was observed between diastolic BP and BMD (P>0.05). When subjects were stratified by obesity status, the non-obese (BMI<25) subjects had a lower BMD for a given level of systolic BP (B=0.00064, 95%CI: 0.00006 to 0.00128, P<0.05), whereas the association was no longer significant among obese (BMI≥25) subjects (P>0.05). Conclusion: Unlike most previous studies, we found a positive association between systolic BP and BMD, which higher systolic BP predicted higher BMD. This association was not significant in obese subjects but existed in non-obese subjects, indicating more studies are needed to explore the mechanisms of BP and obesity on the changes of BMD.