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With Comments from John La Puma, MD, FACP
October 2001; Volume 4; 118
Source: Ackermann RT, et al. Garlic shows promise for improving some cardiovascular risk factors. Arch Intern Med 2001;161: 813-824.
To summarize the effects of garlic on several cardiovascular-related factors and to note its adverse effects, the authors of this study identified English and non-English citations from 11 electronic databases, references, manufacturers, and experts published between January 1966 and February 2000 (depending on the database searched). Reports of cardiovascular-related effects were limited to randomized controlled trials lasting at least four weeks. Reports of adverse effects were not limited by study design.
From 1,798 pertinent records, 45 randomized trials and 73 additional studies were identified that report adverse events. Two physicians abstracted outcomes and assessed adequacy of randomization, blinding, and handling of dropouts. Standardized mean differences of lipid outcomes from placebo-controlled trials were adjusted for baseline differences and pooled using random effects methods.
Compared with placebo, garlic preparations may lead to small reductions in the total cholesterol level at one month (range of average pooled reductions, 0.03-0.45 mmol/L [1.2-17.3 mg/dL]) and at three months (range of average pooled reductions 0.32-0.66 mmol/L [12.4-25.4 mg/dL]), but not at six months. Changes in low-density lipoprotein (LDL) levels and triglyceride levels paralleled total cholesterol level results; no statistically significant changes in high-density lipoprotein levels were observed.
Trials also reported significant reductions in platelet aggregation and mixed effects on blood pressure outcomes. No effects on glycemic-related outcomes were found. Proven adverse effects included malodorous breath and body odor. Other unproven effects included flatulence, esophageal and abdominal pain, allergic reactions, and bleeding.
These trials suggest possible small short-term benefits of garlic on some lipid and antiplatelet factors, insignificant effects on blood pressure, and no effect on glucose levels. Conclusions regarding clinical significance are limited by the marginal quality and short duration of many trials and by the unpredictable release and inadequate definition of active constituents in study preparations.
This highly rigorous meta-analysis of sorts from the University of Texas in San Antonio tried to chew and swallow the garlic literature whole, and emerged with bad breath, but happy. The authors scrutinized "...the internal validity of trials using oral garlic preparations, focused on the importance of differences among various preparations, and comprehensively summarize multiple reported cardiovascular-related effects and potential adverse effects of various oral garlic preparations."
Just the terms used to search the literature give you an idea of how hard they had to look to find everything: "2-propenesulfenic acid," "aglio," "ajo," "ajoene," "alisat," "allicin," "alliinase," "Allium sativum," "allyl mercaptan," "diallyl disulphide," "diallyl sulfide," "diallyl sulphide," "dipropyl disulphide," "dipropyl sulphide," "garlic," "garlic extract," "garlic oil," "knoblauch," "Kwai," "Kyolic," "S-allyl cysteine," "thioallyl derivative," "thiosulfinates," and "vinyl dithiin."
The quality of the 34 trials with double-blind designs was all over the map. Only six studies noted intention-to-treat analyses or reported no dropouts. Different preparations were common (odor-free/odoriferous, dehydrated/not, tablet/powder/oil, standardized/not).
Combining all studies, regardless of garlic preparation, showed that compared with placebo the total cholesterol level and LDL were reduced modestly (see data in the abstract above). Average reductions after 20-24 weeks of treatment were not statistically significant (all garlic preparations, n = 6). The same was true for triglycerides, without 24 week follow-up.
No statistically significant effects were reported for glycosylated hemoglobin, serum insulin and C-peptide levels. Four of 10 trials reported modest but significant decreases in platelet aggregation with garlic treatment compared with placebo.
Approximately half of the trials reported adverse effects—bad breath or body odor (delicately phrased as "malodorous breath or body odor [as perceived by themselves or others]") was the most common.
What makes garlic good medically? From a cardiovascular perspective, many experts think it’s the same component (allicin) that gives its bouquet such magic—which is only created and released on smashing, mincing, dicing, crushing, or chewing the clove. Unfortunately, allicin and alliin are unstable, and they cannot be put in a pill reliably, yet. Of course, there also are issues of soil composition, growth conditions, harvesting procedures, and plant processing.
Without better and better described randomization procedures, adequate (multi-year) trial durations, and thoughtful, opaque blinding to treatment administration and outcome assessments, garlic-as-medicine research cannot bloom.
These authors are experts at evidence-based medicine, and find that some garlic of any kind, if used regularly, likely helps decrease low-density lipoprotein—just a little. Consider it.
It’s a good reason to go to www.garlicislife.com for inspiration, and use the stinking rose in cooking happily.