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Metabolic syndrome is a condition that affects about one quarter of the U.S. population. Characterized by risk factors such as obesity and insulin resistance, metabolic syndrome is often a precursor to type-2 diabetes, heart disease and stroke.
A randomized clinical study of 64 patients with metabolic syndrome, published in 2012, showed that therapeutic phlebotomy significantly reduced systolic blood pressure in patients with metabolic syndrome (SBP decreased from 148.5 ± 12.3 mmHg to 130.5 ± 11.8 mmHg in the phlebotomy group, and from 144.7 ± 14.4 mmHg to 143.8 ± 11.9 mmHg in the control group, reflecting a difference of 16.6 mmHg, 95% CI -20.7 to -12.5, P<0.001).1
Phlebotomy of 300 mL per patient was performed at the beginning of the study for patients in the phlebotomy group and, additionally, a second phlebotomy was performed after 4 weeks, removing between 250 to 500 mL based on serum ferritin. The phlebotomy group also demonstrated significant improvements in other biomarkers such as diastolic blood pressure, insulin resistance, and hemoglobin A1c.
This 2012 report focused on the reduction of body iron stores as a possible mechanism of action for phlebotomy-induced improvements in metabolic and cardiovascular biomarkers, however the study authors also discussed improved blood viscosity as a possible mechanism of action that may have contributed to these effects.
In a separate study of 42 apparently healthy young males, systolic blood viscosity and diastolic blood viscosity were both shown to hold negative correlations with insulin sensitivity (r = -0.41, p=0.007, for both systolic and diastolic viscosity). The authors of this study suggested that blood viscosity may be part of metabolic syndrome and that high blood viscosity itself may increase insulin resistance. The researchers underscored that a hemodynamic mechanism could explain the relationship between viscosity and insulin resistance—“higher whole blood viscosity reduces blood flow and thereby decreases delivery of glucose to skeletal muscle”.2