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Obesity Associated with Elevated Blood Viscosity

Study Shows 15% Higher Blood Viscosity In Obese Patients

Research published in the International Journal of Obesity demonstrates that obese patients (BMI > 28 kg/m2) had diastolic blood viscosity levels that were 15% higher than age and sex matched controls, even in the absence of impaired glucose tolerance, diabetes, hypertension, or hyperlipidaemia.

The results are based on a study of 90 obese subjects (36 men, 54 women) and 90 non-obese subjects matched for age, sex, and smoking habits (36 men, 54 women). Obese subjects with clinical signs of ischemic heart disease, peripheral vascular disease or a history of stroke were excluded from the study. All patients showed normal hepatic and renal function tests and did not suffer from insulin-treated diabetes or any hematological disorder. Average BMI of the obese group was 67% higher than that of the control group (36.2+/-4.8 vs. 21.7 +/- 2.8).

Obesity is a well-known risk factor for cardiovascular disease. Blood viscosity is less known but has been shown to be a strong independent risk factor for cardiovascular disease. Viscosity is determined by and aggregates numerous factors including hematocrit, red cell age and deformability, plasma content including lipids, fibrinogen, and immunoglobulins. In this study, the link between obesity and hyperviscosity may have been mediated by fibrinogen levels, which were on average 40% higher in the obese group than in healthy controls. Increased fibrinogen plays a dual role in increasing blood viscosity: (1) as a high molecular weight protein fibrinogen increases plasma viscosity directly, and (2) fibrinogen enhances erythrocyte aggregation. The latter is likely a significant reason for the increased diastolic blood viscosity levels of the obese group due to the fact that aggregation occurs during diastolic flow.

The study authors concluded: “Blood viscosity is abnormal in obese patients with normal lipid parameters. However, blood viscosity parameters become slightly worse in the presence of additional lipid disturbances... The correlation between body mass index and plasma and whole blood viscosity indicates that the degree of obesity influences blood rheology. Morbid obesity per se even without impaired glucose tolerance, diabetes, hypertension or lipid disturbances may be associated with blood viscosity derangements.”


E. Rillaerts, et al. Blood viscosity in human obesity: Relation to glucose tolerance and insulin status. International Journal of Obesity, (1989) 13, 739-745.


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