Dose-dependent effect of nuts on blood pressure: a systematic review and meta-analysis of randomized controlled trials

ObjectiveTraditional pairwise meta-analyses indicated that nuts consumption can improve blood pressure. We iamed to determine the dose-dependent effect of nuts on systolic (SBP) and diastolic blood pressure (DBP) in adults. MethodsA systematic search was undertaken in PubMed, Scopus, and ISI Web of Science till March 2021. Randomized controlled trials (RCT) evaluating the effects of nuts on SBP and DBP in adults were included. We estimated change in blood pressure for each 20 g/d increment in nut consumption in each trial and then, calculated mean difference (MD) and 95%CI using a random-effects model. We estimated dose-dependent effect using a dose-response meta-analysis of differences in means. The certainty of evidence was rated using the GRADE instrument, with the minimal clinically important difference being considered 2 mmHg. ResultsA total of 31 RCTs with 2784 participants were included. Each 20 g/d increase in nut consumption reduced SBP (MD: -0.50 mmHg, 95%CI: -0.79, -0.21; I2 = 12%, n = 31; GRADE = moderate certainty) and DBP (MD: -0.23 mmHg, 95%CI: -0.38, -0.08; I2 = 0%, n = 31; GRADE = moderate certainty). The effect of nuts on SBP was more evident in patients with type 2 diabetes (MD: -1.31, 95%CI: -2.55, -0.05; I2 = 31%, n = 6). The results were robust in the subgroup of trials with low risk of bias. Levels of SBP decreased proportionally with the increase in nuts consumption up to 40 g/d (MD40g/d: -1.60, 95%CI: -2.63, -0.58), and then appeared to plateau with a slight upward curve. A linear dose-dependent reduction was seen for DBP, with the greatest reduction at 80 g/d (MD80g/d: -0.80, 95%CI: -1.55, -0.04). ConclusionsThe available evidence provides a good indication that nut consumption can result in a small improvement in blood pressure in adults. Well-designed trials are needed to confirm the findings in long term follow-up.