Worldwide, approximately 1 billion people are affected by hypertension and 7 million deaths per year may be attributed to it. Hypertension is typically defined as having a systolic blood pressure >140 mmHg and a diastolic blood pressure >90 mmHg,. It's important to identify safe and effective treatments, if we are to prevent the associated mortality and morbidity of high blood pressure. We did this Cochrane Review to see if garlic might qualify as such a treatment.
Garlic is considered one of the most popular complementary therapies for blood pressure control and is thought to be used by up to 50% of patients with hypertension. Its blood pressure lowering properties appear to come mainly from one of its components, Allicin. This is a vasodilating agent, that has been shown to inhibit angiotensin-converting enzyme, and by doing so it should reduce blood pressure. Recently, a meta-analysis combining hypertensive and normotensive patients provided evidence that garlic consumption lowers blood pressure in this mixed group. But, we felt that it would be important to know about the effects of garlic just within people who have hypertension, as opposed to a mixed population, and to see what garlic consumption does to morbidity and mortality for these patients with hypertension. Unfortunately, we weren't able to go as far as we would have liked, because of the small amount of research that is available.
We found just two trials in which data for hypertensive patients could be extracted and analyzed. In the first trial, 47 hypertensive individuals used 200 mg of garlic powder three times a day versus placebo. After 12 weeks, the average blood pressure in the patients in the garlic powder group had been significantly reduced compared to those in the placebo group. Supine systolic blood pressure was reduced by 12 mmHg and diastolic blood pressure by 9 mmHg. However, no clinical outcome or harm data were reported.
We were unable to analyse the data from the second trial fully, because the authors did not report the number of people randomized to each group. They did report that 200 mg of garlic powder given three times a day, in addition to hydrochlorothiazide-triamterene baseline therapy, produced a 10–11 mmHg reduction in systolic blood pressure and a 6–8 mmHg reduction in diastolic blood pressure, compared to placebo. Once again, though, no clinical outcomes were reported and insufficient data were provided on the safety of garlic powder.
In summary, based on the available evidence, it appears that garlic does reduce blood pressure in hypertensive patients but its impact on clinical outcomes remains uncertain, and little is known about the potential harm associated with garlic therapy.