A benchmark research study published in 1998 in the American Journal of Epidemiology demonstrated an 88% reduced risk of sudden heart attack (acute myocardial infarction, or AMI) in regular blood donors. Results published in Clinical Hemorheology and Microcirculation the same year demonstrated that blood donation reduced systolic and diastolic blood viscosity values from their baselines by 21% and 32%, respectively.
The first study was a prospective epidemiological study following 2,862 men aged 42-60 for an average of 9 years. Only one out of the 153 men (or 0.7%) who had donated blood in the 24 months preceding the baseline examination experienced an acute myocardial infarction during 1984 to 1995, whereas 316 men (12.5%) of 2,529 non-blood donors had an AMI (p < 0.0001 for difference between proportions). The study authors adjusted for age, examination years and all other predictive coronary disease risk factors and found the blood donors had an 88% reduced risk of AMI compared with non-blood donors.
The second study examined 30 patients (12 male, 18 female) who donated one unit (450 +/- 30 mL) every four days for a total of four donation sessions. Blood viscosity measurements were taken at baseline and at the end of the four sessions. Systolic blood viscosity was reduced by 21%, and diastolic blood viscosity was reduced by 32%, on average.
Donation of blood not only causes hemodilution but also erythropoiesis, or the formation of new red blood cells. The new, younger cells have more deformable membranes and less of a tendency to aggregate. In fact, old cells have been shown to be 30% more rigid and to aggregate 80% more than new cells. [Muravyov] The improved circulation from a larger proportion of young cells causes less damage to the vessel wall leading to a reduction in the buildup of atherosclerotic plaque and plaque rupture.