Han B, Nazary-Vannani A, Talaei S, et al. The effect of green coffee extract supplementation on blood pressure: a systematic review and meta-analysis of randomized controlled trials. Phytother Res. November 2019;33(11):2918-2926. doi: 10.1002/ptr.6481.
Hypertension is major risk factor for cardiovascular disease and is associated with stroke, kidney problems, disability, and early mortality. Drug therapies and lifestyle changes are used to reduce blood pressure; however, many studies have reported reduced blood pressure with the use of antioxidant vitamins, supplements, and other nutritional supplements. Coffee (Coffea arabica, Rubiaceae) has been shown to have beneficial effects on liver function, diabetes mellitus, and degenerative diseases. Unroasted green coffee contains chlorogenic acid (CGA), which possesses antidiabetic, antiobesity, and antilipidemic properties. These authors conducted a systematic review and meta-analysis of studies investigating the efficacy and effectiveness of supplementation with green coffee bean extract (GCBE) on lowering blood pressure.
The authors searched PubMed/Medline, Scopus, the Cochrane Library, and Google Scholar to identify clinical trials investigating the effects of GCBE on systolic blood pressure (SBP) and diastolic blood pressure (DBP) up to February 2019. They sought reports of randomized, placebo-controlled trials with crossover or parallel designs that included participants older than 18 years, reported sufficient data on baseline and final results of SBP or/and DBP in both GCBE and control groups, and used any green coffee species as interventions. Of the 129 articles that were screened, 103 were excluded based on their title and abstract. Twenty-one of the remaining 26 full-text articles were excluded for various reasons, leaving five articles with nine studies in the meta-analysis.
The included articles were published between 2004 and 2018. The studies were conducted in Iran, South Korea, and Japan; ranged in duration from four to 16 weeks; and used daily doses of GCBE between 46 mg and 800 mg. All trials were parallel-group studies. One trial included females only, four studies included males only, and four studies included both genders. The study populations ranged from 31 to 72 participants, including patients with metabolic syndrome, healthy participants, and patients with hypertension. Most studies were of adequate quality; one was rated as fair quality for blinding of outcome assessment.
All studies (including 501 participants) reported SBP as an outcome measure. Overall, results indicated GCBE significantly decreased SBP (P < 0.001), with no significant heterogeneity found among the studies. The results remained significant in analyses of subgroups of patients with hypertension and patients with metabolic syndrome. Greater reductions in SBP were observed with the use of 400 mg or more of GCBE (P = 0.030) and when used for four weeks (P < 0.001).
All nine studies also reported DBP as an outcome measure. DBP decreased significantly after GCBE supplementation (P < 0.001), with low heterogeneity found among the studies. In the subgroup analyses, decreases in DBP were seen only in patients with hypertension (P < 0.001). GCBE reduced DBP in studies lasting four weeks and using < 400 mg of GCBE. Reports of adverse effects among the studies suggest that the interventions were generally safe.
The authors found no evidence of publication bias in the meta-analysis. This study has several limitations, which are acknowledged by the authors. Lifestyle adjustments may have influenced the results. CGA is available in many foods, and individuals may consume about 1 g of CGA daily. Whether the extra amount of CGA consumed by the study participants enhanced its effect on blood pressure is unclear. The analyses were not restricted to participants of only one type (as some were healthy and others were not), which could have affected the mechanism of action and effectiveness of the treatment. Some trials included small study populations.
"The results of the current meta-analysis study support the use of GCBE supplementation for the improvement of blood pressure indices, with subgroup analysis highlighting improvements in hypertensive patients," conclude the authors.
The authors declare no conflict of interest.