Blueberries improve endothelial function, but not blood pressure, in adults with metabolic syndrome: a randomized, double-blind, placebo-controlled clinical trial

Abstract

Blueberry consumption has been shown to have various health benefits in humans. However, little is known about the effect of blueberry consumption on blood pressure, endothelial function and insulin sensitivity in humans. The present study investigated the role of blueberry consumption on modifying blood pressure in subjects with metabolic syndrome. In addition, endothelial function and insulin sensitivity (secondary measurements) were also assessed. A double-blind and placebo-controlled study was conducted in 44 adults (blueberry, n = 23; and placebo, n = 21). They were randomized to receive a blueberry or placebo smoothie twice daily for six weeks. Twenty-four-hour ambulatory blood pressure, endothelial function and insulin sensitivity were assessed pre- and post-intervention. The blood pressure and insulin sensitivity did not differ between the blueberry and placebo groups. However, the mean change in resting endothelial function, expressed as reactive hyperemia index (RHI), was improved significantly more in the group consuming the blueberries versus the placebo group (p = 0.024). Even after adjusting for confounding factors, i.e., the percent body fat and gender, the blueberry group still had a greater improvement in endothelial function when compared to their counterpart (RHI; 0.32 ± 0.13 versus -0.33 ± 0.14; p = 0.0023). In conclusion, daily dietary consumption of blueberries did not improve blood pressure, but improved (i.e., increased) endothelial function over six weeks in subjects with metabolic syndrome.

Keywords: blueberries; cardiovascular risk factors; endothelial dysfunction; endothelial function; hypertension; prediabetes.

Figure 1

Consolidated Standards of Reporting Trials (CONSORT) flow diagram of participants from recruitment to data analysis.

Figure 2

(A) Change in RHI (Δ; post- minus pre-intervention) in individual humans with metabolic syndrome who consumed the blueberry or placebo smoothie for six weeks; (B) mean change in RHI after adjusting for percentage of body fat and gender. * p = 0.0023 between groups (blueberry versus placebo). RHI, reactive hyperemia index (i.e., endothelial function). Values are the means ± SEM, n = 22 (blueberry) or n = 18 (placebo).