Data published in the Journal of Clinical Hypertension indicated that garlic supplements could reduce systolic and diastolic blood pressure by an average of 3.75 mmHg and 3.39 mmHg, respectively.
Additional number crunching showed that the benefits were only significant for people with elevated blood pressure (hypertension).
“Our meta-analysis suggests that garlic supplementation is superior to placebo in reducing blood pressure in hypertensive patients, especially in those with high systolic blood pressure,” wrote the authors from the First Affiliated Hospital of Soochow University in China.
Consumer awareness of the health benefits of garlic, mostly in terms of cardiovascular and immune system health, has benefited the supplements industry, particularly since consumers seek the benefits of garlic without the odors that accompany the fresh bulb.
The benefits have been linked to the compound allicin, which is not found in fresh garlic; It is only formed when garlic is crushed, which breaks down a compound called diallyl sulphide.
The 17 RCTs included supplements formulated with garlic powder, aged garlic extract, and garlic oil, with the majority using garlic powder in dosages ranging from 300 mg/d to 900 mg/d. These doses would provide daily amounts of allicin of between 1.8 mg and 5.4 mg.
Commenting on the potential mechanism, the authors noted that this is still not clear but several hypotheses have been proposed, including the antioxidant activity of allicin to counter the detrimental effects of oxidative stress on endothelial health, or via inhibition of angiotensin-converting enzymes (ACEs) by allicin.
“[S]everal dipeptides extracted from garlic have also been reported to inhibit ACE, and allicin may not be the only compound that has ACE inhibitory activity. Nonetheless, garlic can decrease blood pressure by inhibiting ACE,” they wrote.
In addition, no effect of the dose could be determined by the scientists.
“Because the studies reported multiple dosages and the duration was limited, it was difficult for us to detect an association between the dosage and duration with blood pressure change,” they wrote.
Garlic and heart health
The meta-analysis adds to the large body of science supporting the cardiovascular benefits of garlic. A recent meta-analysis, published in the Journal of the Science of Food and Agriculture (doi: 10.1002/jsfa.5557), concluded that garlic may also reduce cholesterol and triglyceride levels.
Researchers from Shandong University reported that, compared with placebo groups, garlic consumption is associated with a 5.4% reduction in cholesterol levels and a 6.5% reduction in triglyceride levels.
Garlic has been suggested to exhibit several health benefits, including inhibiting enzymes involved in lipid synthesis, decreasing platelet aggregation, preventing lipid peroxidation, and increasing antioxidant status.
Source: Journal of Clinical Hypertension
Published online ahead of print, doi: 10.1111/jch.12473
“Effect of Garlic on Blood Pressure: A Meta-Analysis”
Authors: H. Wang, J. Yang, L. Qin, X. Yang