Garlic powder intake and cardiovascular risk factors: a meta-analysis of randomized controlled clinical trials

Abstract

Background/objectives: Although preclinical studies suggest that garlic has potential preventive effects on cardiovascular disease (CVD) risk factors, clinical trials and reports from systematic reviews or meta-analyses present inconsistent results. The contradiction might be attributed to variations in the manufacturing process that can markedly influence the composition of garlic products. To investigate this issue further, we performed a meta-analysis of the effects of garlic powder on CVD risk factors.

Materials/methods: We searched PubMed, Cochrane, Science Direct and EMBASE through May 2014. A random-effects meta-analysis was performed on 22 trials reporting total cholesterol (TC), 17 trials reporting LDL cholesterol (LDL-C), 18 trials reporting HDL cholesterol (HDL-C), 4 trials reporting fasting blood glucose (FBG), 9 trials reporting systolic blood pressure (SBP) and 10 trials reporting diastolic blood pressure (DBP).

Results: The overall garlic powder intake significantly reduced blood TC and LDL-C by -0.41 mmol/L (95% confidence interval [CI], -0.69, -0.12) (-15.83 mg/dL [95% CI, -26.64, -4.63]) and -0.21 mmol/L (95% CI, -0.40, -0.03) (-8.11 mg/dL [95% CI, -15.44, -1.16]), respectively. The mean difference in the reduction of FBG levels was -0.96 mmol/L (95% CI, -1.91, -0.01) (-17.30 mg/dL [95% CI, -34.41, -0.18]). Evidence for SBP and DBP reduction in the garlic supplementation group was also demonstrated by decreases of -4.34 mmHg (95% CI, -8.38, -0.29) and -2.36 mmHg (95% CI, -4.56, -0.15), respectively.

Conclusions: This meta-analysis provides consistent evidence that garlic powder intake reduces the CVD risk factors of TC, LDL-C, FBG and BP.

Keywords: Allium sativum; CVD risk factor; garlic; meta-analysis; systematic review.

Fig. 1

Flow diagram of the article selection process.

Fig. 2

Forest plot results of the effect of garlic powder on cholesterol. (A) Total cholesterol, (B) LDL-cholesterol and (C) HDL-cholesterol; WMD, weighted mean difference

Fig. 3

Forest plot results of the effect of garlic powder on fasting blood glucose; WMD, weighted mean difference

Fig. 4

Forest plot results of the effect of garlic powder on blood pressure. (A) SBP and (B) DBP; WMD, weighted mean difference

Fig. 5

Meta-regression analysis between changes in cardiovascular disease risk factors and garlic powder dosage. (A) Total cholesterol, (B) LDL-cholesterol, (C) HDL-cholesterol, (D) systolic blood pressure and (E) diastolic blood pressure.

Fig. 6

Meta-regression analysis between changes in cardiovascular disease risk factors and duration of garlic powder supplementation. (A) Total cholesterol, (B) LDL-cholesterol, (C) HDL-cholesterol, (D) systolic blood pressure and (E) diastolic blood pressure.

Fig. 7

Meta-regression analysis between changes in cardiovascular disease risk factors and study quality regarding garlic powder supplementation. (A) Total cholesterol, (B) LDL-cholesterol, (C) HDL-cholesterol, (D) systolic blood pressure and E) diastolic blood pressure.

Fig. 8

Meta-regression analysis between changes in cardiovascular disease risk factors and baseline values of (A) total cholesterol, (B) LDL-cholesterol, (C) HDL-cholesterol, (D) systolic blood pressure and (E) diastolic blood pressure.

Fig. 9

Meta-regression analysis between changes in cardiovascular disease risk factors and number of participants. (A) Total cholesterol, (B) LDL-cholesterol, (C) HDL-cholesterol, (D) systolic blood pressure and (E) diastolic blood pressure.

Fig. 10

Funnel plot showing the effects of the garlic powder intervention on changes in (A) total cholesterol, (B) LDL-cholesterol, (C) HDL-cholesterol, (D) fasting blood glucose, (E) systolic blood pressure and (F) diastolic blood pressure.