Blood viscosity as a continuous marker of cardio-metabolic risk burden: a large-scale cross-sectional study of 38,574 adults

Metabolic syndrome (MetS) is diagnosed using fixed thresholds that may not fully reflect the continuous accumulation of cardio-metabolic risk. We investigated whether whole blood viscosity (WBV) increases progressively with increasing MetS burden and explored the relative contribution of individual MetS components to hemorheologic alterations.

We analyzed 38,574 adults (21,914 men and 16,660 women) who underwent comprehensive health examinations between January and April 2021. Whole blood viscosity was measured by cone-plate viscometry at shear rates of 300 s^-1 (systolic blood viscosity [SBV]) and 5 s^-1 (diastolic blood viscosity [DBV]). MetS was defined according to NCEP-ATP III criteria. Associations between WBV and MetS burden were evaluated using logistic regression, ANCOVA, regression tree analyses, ROC analyses, and sex-by-viscosity interaction testing.

WBV increased progressively with each additional MetS component in both sexes (p for trend <0.001). After full adjustment for hematocrit, age, smoking status, eGFR, white blood cell count, and AST/ALT, higher SBV was associated with MetS in both women (OR 1.45, 95% CI 1.32-1.58, per 1-SD increase) and men (OR 1.27, 95% CI 1.22-1.33, per 1-SD increase). Regression tree analyses identified triglycerides and waist circumference as metabolic factors associated with elevated WBV. Sex-stratified analyses demonstrated a stronger association between WBV and MetS in women than in men.

WBV increased in parallel with accumulating cardio-metabolic risk burden, including among individuals who did not meet diagnostic criteria for MetS. WBV may serve as a complementary marker associated with metabolic risk burden, particularly among women and individuals with hypertriglyceridemia or central adiposity.