In chronic heart failure (CHF), the heart muscle does not pump blood well enough to meet the body’s need for blood and oxygen. CHF is caused by high blood pressure, coronary artery disease, and other cardiovascular conditions. It is a common cause of death in older people. Garlic (Allium sativum, Amaryllidaceae) bulb has been shown to lower blood pressure, blood lipid levels, and inflammation in people with heart disease. Black garlic (BG) is garlic that has been fermented and aged under conditions of high temperature and high humidity. BG has antioxidant, anti-inflammatory, and antidiabetic effects, but the effects of BG in people with CHF are not known. The purpose of this randomized controlled trial was to evaluate the effects of BG on chronic heart failure in patients with coronary heart disease.
Patients with CHF caused by coronary heart disease were enrolled at Jilin University in Changchun, China from May 1, 2016, to June 30, 2017. Patients were included if they were 35-75 years old, met the Framingham and Boston heart failure criteria, had coronary heart disease confirmed by an echocardiogram, and had left ventricular ejection fraction (LVEF) ≤ 50% and heart function classes II-III using the New York Heart Association classification. Patients were excluded if they had an acute coronary syndrome, “combined shock,” severe valvular heart disease, other systemic diseases, any condition affecting lower limb function, including arthritis and recent knee surgery, MRSA infection, or planned surgery. Patients continued with their prescribed heart failure treatments during the trial, which included multiple interventions.
Patients were randomly assigned to the BG group or placebo group. Additionally, all were prescribed 30 minutes of walking exercise five times weekly. The BG group took 20 g BG daily for six months. The black garlic was purchased from Shandong Sanjin Black Garlic Industry Co., Ltd. in Jinzian, China. The garlic was prepared by fermenting fresh garlic at 140-176°F (60-80°C) and 70-95% humidity for 50 days. The composition of BG was analyzed using gas chromatography/mass spectrophotometry (GC/MS), and several assays were conducted to evaluate the antioxidant activity of BG. The article did not describe the dosage form used in the trial, and it is not known how the patients consumed the BG each day. The article does not describe a placebo product, and it is not clear if patients in the placebo group took a placebo or were simply a control group. The following tests were performed before and after the intervention: quality of life using the Minnesota Living with Heart Failure Questionnaire (MLHFQ); LVEF; six-minute walk test; and blood levels of lipids, antioxidants, blood urea nitrogen (BUN), serum creatinine, and N-terminal pro-brain natriuretic peptide (Nt-proBNP), which is a precursor of the BNP hormone that increases with severity of heart failure.
A total of 120 patients were recruited, evenly divided between the BG and placebo groups. Clinical characteristics were similar between patients in the BG and placebo groups at baseline. It appears that there were no dropouts. Improvement in MLHFQ quality of life score was significantly greater in the BG group compared to the placebo group (P = 0.02), although both groups improved significantly (P = 0.01). LVEF increased in both groups (both P = 0.01), but the improvement was significantly greater for the BG group compared to the placebo group (P < 0.03). Mean LVEF increased from 28.24±8.15% to 32.73±10.21% in the placebo group, and from 29.36±9.34% to 36.82±10.43% in the BG group. Improvement in the six-minute walk test was significantly greater in the BG group compared to the placebo group (P = 0.02): the increase in mean distance walked was 24.51 m in the placebo group and 69.94 m in the BG group.
Nt-proBNP levels decreased in both groups, and the improvement was significantly greater for the BG group compared to the placebo group (P = 0.03). Levels of the antioxidant enzymes glutathione peroxidase and superoxide dismutase increased significantly in the BG group compared to the placebo group (both P < 0.05). Levels of nitric oxide and malondialdehyde, an indicator of lipid oxidation, decreased significantly in the BG group compared to the placebo group (both P < 0.05). BUN and serum creatinine decreased in both groups, but more so in the BG group (P = 0.02 for both). The article did not report blood lipid levels before and after the intervention. The Lee Score, which estimates the risk of a cardiac event occurring, decreased in both groups and the improvement was significantly greater for the BG group compared to the placebo group (P = 0.02). It was reported that “no obvious adverse reactions occurred” during the trial.
The total phenolic content of BG was 2.60 mg gallic acid equivalents (GAE)/g, while the total phenolic content of raw garlic was 0.49 mg GAE/g. Oxygen Radical Absorbance Capacity (ORAC), which estimates total antioxidant capacity, was 984.56 μmol Trolox equivalents (TE)/g for BG and 324.43 μmol TE/g μmol for raw garlic. The antioxidant activity was significantly greater for BG than raw garlic for all antioxidant assays (ORAC, ferric iron reduction, and free radical scavenging of synthetic compounds assays; all P < 0.05).
The authors conclude that BG has many health-promoting properties and that BG may improve heart disease symptoms by increasing antioxidant activity. However, assuming that the placebo group did not consume raw garlic, their study did not actually generate evidence that the antioxidant activity of BG was related to the improvement in cardiac performance. They recommend further work to confirm their findings, given the short duration and small sample size of the trial. The article could have been strengthened by providing more details about the black garlic intervention and study design. Since the nature of the “placebo” or control group is unknown, it is not clear if the patients or researchers were blinded to the group assignment. The placebo group showed significant improvements in most study outcomes, which the authors did not address. Their use of exercise therapy and conventional medications likely suffices to explain that outcome. Although blood lipid levels were to be measured in the trial, no results were reported. Many patients likely had elevated blood lipids, and it would have been informative to learn whether black garlic has the same lipid-lowering effects as regular garlic.
The authors declare no conflict of interest.
Liu J, Zhang G, Cong X, Wen C. Black garlic improves heart function in patients with coronary heart disease by improving circulating antioxidant levels. Front Physiol. November 1, 2018;9:1435. doi: 10.3389/fphys.2018.01435.