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Important evidence for the link between blood viscosity and cardiovascular events was provided by the Edinburgh Artery Study in a random population of 1,592 men and women aged 55 to 74 years, who were followed over a mean period of 5 years. After adjustment for age and gender, mean values for both blood viscosity and hematocrit-adjusted blood viscosity were elevated in patients who experienced cardiovascular events (ischemic heart attacks and strokes) relative to those who did not. The differences in blood viscosity were statistically significant (p=0.0003), and the link between blood viscosity and the occurrence of cardiovascular events was at least as strong as that of diastolic blood pressure and LDL cholesterol and stronger than that of smoking.1
In a seminal report just prior to the publication of the Edinburgh Artery Study, Lousiana State University pathologist Gregory Sloop proposed that blood viscosity is the one unifying mechanism by which all established cardiovascular risk factors promote atherosclerosis, including LDL cholesterol, high blood pressure, diabetes, obesity and smoking.2 Numerous studies have confirmed the linkages between blood viscosity and the following cardiovascular risk factors:
- Hypertension 3-6
- Hyperlipidema: positive correlation with LDL cholesterol, total cholesterol and triglycerides; negative correlation with HDL cholesterol 7-13
- Diabetes, insulin resistance syndrome and obesity 12,14-18
- Tobacco smoking 6,19-21
- Male gender vs. premenopausal women 12-13,22-23
- Aging 12,21,24
In his report, which was titled A Unifying Theory of Atherogenesis, Dr. Sloop indicated that blood viscosity was uniquely suited to predict the entire course of cardiovascular disease because blood viscosity accomplishes the following: (i) accounts for the morphological similarity of atherosclerotic lesions associated with many diverse risk factors, (ii) explains the anatomic distribution of lesions throughout the body, (iii) provides a role for platelet activation by turbulent blood flow caused by hyperviscosity, (iv) includes an explanation of the protective role of HDL cholesterol (i.e., HDL has been shown experimentally to lower viscosity).2
Blood viscosity holds certain similarities with blood pressure. Like blood pressure, the viscosity of blood changes during each cardiac cycle and is reported using two numerical quantities: systolic and diastolic viscosity. However, while blood pressure is parameter of the circulatory system as a whole, blood viscosity is a parameter specific to the fluid flowing through the system. Therefore, viscosity can be said to precede pressure and to be biophysically more fundamental than pressure.
7. Sloop GD, Garber DW. The effects of low-density lipoprotein and high-density lipoprotein on blood viscosity correlate with their association with risk of atherosclerosis in humans. Clin Sci 1997; 92:473-479.
12. de Simone G, Devereux RB, Chien S, et al. Relation of blood viscosity to demographic and physiologic variables and to cardiovascular risk factors in apparently normal adults. Circulation 1990; 81:107-17.
14. Tamariz LJ, Young JH, Pankow JS, et al. Blood viscosity and hematocrit as risk factors for type 2 diabetes mellitus: The Atherosclerosis Risk in Communities (ARIC) Study. Am J Epidemiol 2008; 168:1153-60.
15. Jax TW, Peters AJ, Plehn G, Schoebel FC. Hemostatic risk factors in patients with coronary artery disease and type 2 diabetes - a two year follow-up of 243 patients. Cardiovasc Diabetol 2009; 8:48.
23. Fowkes FG, Pell JP, Donnan PT, et al. Sex differences in susceptibility to etiologic factors for peripheral atherosclerosis. Importance of plasma fibrinogen and blood viscosity. Arterioscler Thromb 1994; 14:862-8.