Garlic is an oft-touted natural remedy, particularly with regard to affairs of the heart: regular garlic consumption has been said to improve cardiovascular health. In the past, one mechanism that has been said through which garlic can exert a heart-healthy effect is by some ability to reduce blood pressure. A previous review of the evidence in the area found that of 7 trials in which the effects of garlic (powder) was compared with placebo, three showed a significant reduction in systolic blood pressure (the higher blood pressure value), while 4 showed a significant reduction in diastolic blood pressure (the lower blood pressure value). Overall, the results indicated that garlic had genuine blood pressure lowering potential [1].
Since this review was published, other evidence has come to light. Recently, scientists brought the state of the science on this topic up to date with a meta-analysis which combined the results of 11 relevant studies [2]. The amassed results demonstrated:
Overall, a statistically significant reduction in systolic blood pressure (an average reduction of 4.6 mmHg)
Overall, no statistically significant reduction in diastolic blood pressure
The authors of this study also went on to separate out the data from individuals in studies who were deemed to have high blood pressure (blood pressure of 140/90 mmHg or higher).
In this group, the results showed:
A statistically significant reduction in systolic blood pressure (an average reduction of 8.4 mmHg)
A statistically significant reduction in systolic blood pressure (an average reduction of 7.3 mmHg)
The authors point out that if the overall effect of garlic on blood pressure seen found in the review were applied to the population as a whole, risk of cardiovascular disease and death from cardiovascular disease would be expected to fall by 8-20 per cent. It should be perhaps borne in mind that garlic might possibly reduce the risk of cardiovascular disease by other mechanisms as well, notably an anti-coagulant effect (garlic is a ‘blood-thinner’, like aspirin).
The dosages of garlic used in the studies on blood pressure were 600 mg to 900 mg. One of garlic’s main active ingredients is believed to be allicin. The dosages used in the studies would translate to a daily allicin dose of 3.6 mg to 5.4 mg. One single fresh close of garlic contains 5 mg to 9 mg of allicin. For maximum effect, the garlic should be raw (uncooked).
References:
1. Silagy CA, et al. A meta-analysis of the effect of garlic on blood pressure.
J Hypertens. 1994 Apr;12(4):463-8.
