Osteoporosis is a degenerative often age-related condition of the bone, resulting in a weakening and thinning of bones, as well as possible fractures. A cross-sectional, case-controlled study, performed at Harbin Medical University, evaluated the relationship between blood flow parameters and bone mineral density (BMD) in 318 elderly Chinese patients and 163 controls matched for type 2 diabetes and hypertension.
The clinical study included a stepwise multivariate regression analysis which showed significant negative correlation between lumbar spine (L2-4) BMD and whole blood viscosity (WBV) at low shear (3 s-1) and high shear (200 s-1), (β = -0.513; p < 0.001 and β = -0.089; P < 0.001, respectively).1 Low shear WBV also showed a significant negative correlation with femoral neck BMD (β – -0.157; p = 0.003).
Elevated diastolic blood viscosity (low shear viscosity) had the strongest correlation to low BMD. The largest differences in WBV were observed in patients with osteoporosis with matched controls, however patients with osteopenia also showed increases relative to the control group.
Authors of the study, Teng et al., were unable to elucidate the cause of these correlations although they stated that blood viscosity and osteoporosis share similar risk factors such as inflammation, age, smoking, physical activity, and estrogen deficiency due to menopause. Viscous forces are predominant at low shear and directly influence the ability of blood to flow within the microvasculature. Since thick blood at low shear rates showed the strongest correlation to reduced bone mineral density, inadequate perfusion of the microvasculature may also contribute to the pathology of osteoporosis.
While this study design certainly does not demonstrate causality, it provides rationale for future prospective clinical studies to determine the clinical implications of elevated diastolic blood viscosity (low shear) levels in osteoporosis treatment and prevention.