The largest blood viscosity study ever conducted was part of the Edinburgh Artery Study in the 1990s, which followed a random population of 1,592 middle-aged adults for a mean of 5 years. It showed that blood viscosity, after adjustment for age and sex, was significantly higher in patients experiencing heart attacks and strokes than those who did not (p = 0.0003). The 20% of the individuals with the highest viscosity had 55% of the heart attacks and strokes during the 5-year period. In contrast, only 4% of those in the lowest viscosity group had any significant events.
What is remarkable is that these findings were based solely on measuring systolic blood viscosity. Even so, the link between systolic blood viscosity and acute cardiovascular events was statistically as strong as the links that diastolic blood pressure or LDL cholesterol had with cardiovascular events. Systolic viscosity was a stronger predictor of heart attacks and strokes than smoking.
Survival curves (cardiovascular event-free survival) for males with high blood pressure. Diastolic blood viscosity was measured at the beginning of the clinical study, and patients were divided equally into 3 groups according to viscosity levels then followed for up to 12 years.
In a prospective study, 331 middle-aged men with high blood pressure were followed for up to 12 years after measuring diastolic blood viscosity. The patients were divided into three groups according to viscosity levels: those in the highest tertile had more than three times more cardiovascular deaths than those in the lowest tertile (hazard ratio = 3.42, 95% confidence interval = 1.4–8.4, p = 0.006).