livin' raw...

Ronald T. Ackermann, MD; Cynthia D. Mulrow, MD, MSc; Gilbert Ramirez, DrPH; Christopher D. Gardner, PhD; Laura Morbidoni, MD; Valerie A. Lawrence, MD, MSc

Arch Intern Med. 2001;161:813-824.

Objectives To summarize the effects of garlic on several cardiovascular-related factors and to note its adverse effects.

Methods English and non-English citations were identified from 11 electronic databases, references, manufacturers, and experts from January 1966 through February 2000 (depending on the database searched). Reports of cardiovascular-related effects were limited to randomized controlled trials lasting at least 4 weeks. Reports of adverse effects were not limited by study design. From 1798 pertinent records, 45 randomized trials and 73 additional studies reporting adverse events were identified. 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.

Results Compared with placebo, garlic preparations may lead to small reductions in the total cholesterol level at 1 month (range of average pooled reductions, 0.03-0.45 mmol/L [1.2-17.3 mg/dL]) and at 3 months (range of average pooled reductions 0.32-0.66 mmol/L [12.4-25.4 mg/dL]), but not at 6 months. Changes in low-density lipoprotein 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.

Conclusions 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.


From the San Antonio Evidence-based Practice Center, University of Texas Health Science Center (Drs Ackermann, Mulrow, Ramirez, and Lawrence), Veterans Evidence-based Research Dissemination Implementation Center, Audie L. Murphy Memorial Veterans Hospital, San Antonio (Drs Mulrow, Ramirez, and Lawrence); Center for Research in Disease Prevention, Stanford University, Palo Alto, Calif (Dr Gardner); and the Istituto di Clinica Medica Universita degli Studi di Ancona, Ancona, Italy (Dr Morbidoni). Dr Gardner is now with the Center for Advanced Studies in Nutrition and Social Marketing, University of California, Davis.