Effects of blueberry supplementation on blood pressure: a systematic review and meta-analysis of randomized clinical trials

Blueberries belong to the genus Vaccinium of the family Ericaceae. A series of epidemiological studies have demonstrated that blueberry polyphenols, particularly blueberry anthocyanins provide significant beneficial effects for humans. However, the findings of clinical studies have been equivocal. Therefore, we sought to assess the potential anti-hypertensive effects of blueberry supplementation through a meta-analysis of available randomized controlled trials (RCTs). A comprehensive literature search of PubMed, The Cochrane Library, AMED (Allied and Complementary Medicine Database), Embase, Web of Science, Wanfang Database, and China National Knowledge Infrastructure were performed to identify potential studies published before June 2015. The standardized mean difference and 95% confidence interval (CI) were used as summary statistics. Net changes in systolic blood pressure (SBP) and diastolic blood pressure (DBP) between the blueberry and placebo groups were calculated by subtracting the values at the end of follow-up from those at baseline. Meta-regression was used to identify potential moderators of effect size. Six RCT studies with 204 participants were included in our meta-analysis. There was no significant effect of blueberry supplementation on changes in blood pressure (BP) relative to baseline, and there was a mean difference of -0.28 (95% CI: -1.11 to 0.56, I-2 = 87%) and -0.5 (95% CI: -1.24 to 0.24, I2 = 84%) mmHg for SBP and DBP, respectively. In summary, the results from this meta-analysis do not favor any clinical efficacy of blueberry supplementation in improving BP. Further well-designed larger RCTs are required to verify the association between blueberry supplementation and BP.