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.
I took myself off my high blood pressure pills after two readings that it was normal. I have a very slow pulse, low temp. and used to have, when a bit younger, low blood pressure. Instead I eat a clove of raw garlic for breakfast and glue it onto my wholemeal bread with honey. I will let you know when next I visit my GP whether it is working.
Dr B, previously you have dismissed evidence from other systematic reviews and the conclusions of metanalysis as merely someone’s “opinion”, yet now you seem happy to quote these type of sources as evidence when it comes to garlic.
Perhaps I can remind you of what you yourself said in the WHI thread when you were asked about the conclusions of a systematic review:
Does this mean you now are going to enlighten us about the scientific evidence from each of the 25 specific individual studies on garlic?
PS – I am actually quite happy to accept your evidence as it stands. I am comfortable with the idea of accepting the conclusions drawn by experts through the process of systematic review. It is just that you have previously said you were not, so I wondered why your opinion has now changed.
david
“Dr B, previously you have dismissed evidence from other systematic reviews and the conclusions of metanalysis as merely someone’s “opinion”
I didn’t dismiss the “evidence” David. I asked superburger (or anyone) to quote the evidence which supported the conclusions the authors came to (that’s not the same thing, is it?). Seems to me the authors put a positive spin on some pretty dismal results.
The difference with the garlic meta-analysis is that the individual studies do seem to support the authors’ conclusions. And that difference is critical (obviously).
But the most important thing, David, is that superburger cited the Cochrane review as evidence to support his assertion that “there is plenty of evidence that a diet low in saturated fat can reduce CHD”. Yet, the results of the Cochrane review do not support his assertions. If they did, then it was a simple matter for him (or anyone) to quote the actual studies. In other words, superburger has made supposedly evidence-based claims but is unable to validate these scientifically. I’m sure you can see the problem with that, can’t you?
I read that more effective health results were achieved with crushed garlic than chopped. I wonder why that would be?
Dr. B,
my friend and I were debating this the other day. My friend said since he already had low blood pressure he was afraid eating garlic would lower it even more. My question is whether eating too much garlic would lower blood pressure to an unsafe level? Thanks Dr. B