Among all fruits, berries have shown substantial cardio-protective benefits due to their high polyphenol content. However, investigation of their efficacy in improving features of metabolic syndrome and related cardiovascular risk factors in obesity is limited. We examined the effects of blueberry supplementation on features of metabolic syndrome, lipid peroxidation, and inflammation in obese men and women. Forty-eight participants with metabolic syndrome [4 males and 44 females; BMI: 37.8 +/- 2.3 kg/m(2); age: 50.0 +/- 3.0 y (mean +/- SE)] consumed freeze-dried blueberry beverage (50 g freeze-dried blueberries, approximately 350 g fresh blueberries) or equivalent amounts of fluids (controls, 960 mL water) daily for 8 wk in a randomized controlled trial. Anthropometric and blood pressure measurements, assessment of dietary intakes, and fasting blood draws were conducted at screening and at wk 4 and 8 of the study. The decreases in systolic and diastolic blood pressures were greater in the blueberry-supplemented group (- 6 and - 4%, respectively) than in controls (- 1.5 and - 1.2%) (P lt 0.05), whereas the serum glucose concentration and lipid profiles were not affected. The decreases in plasma oxidized LDL and serum malondialdehyde and hydroxynonenal concentrations were greater in the blueberry group (- 28 and - 17%, respectively) than in the control group (- 9 and - 9%) (P lt 0.01). Our study shows blueberries may improve selected features of metabolic syndrome and related cardiovascular risk factors at dietary achievable doses.