Garlic - Research
The efficacy of Bulbus Allii Sativi as a carminative has been demonstrated in human studies. A clinical study of 29 patients taking two tablets daily (~1000 mg/day) of a dried garlic preparation demonstrated that garlic relieved epigastric and abdominal distress, belching, flatulence, colic, and nausea, as compared with placebo (32). It was concluded that garlic sedated the stomach and intestines, and relaxed spasms, retarded hyperperistalsis, and dispersed gas (32).
A meta-analysis of the effect of Bulbus Allii Sativi on blood pressure reviewed a total of 11 randomized, controlled trials (published and unpublished) (113, 114). Each of the trials used dried garlic powder (tablets) at a dose of 600– 900mg daily (equivalent to 1.8–2.7 g/day fresh garlic). The median duration of the trials was 12 weeks. Eight of the trials with data from 415 subjects were included in the analysis; three trials were excluded owing to a lack of data. Only three of the trials specifically used hypertensive subjects, and many of the studies suffered from methodological flaws. Of the seven studies that compared garlic with placebo, three reported a decrease in systolic blood pressure, and four studies reported a decrease in diastolic blood pressure (115). The results of the meta-analysis led to the conclusion that garlic may have some clinical usefulness in mild hypertension, but there is still insufficient evidence to recommend the drug as a routine clinical therapy for the treatment of hypertension (115).
A meta-analysis of the effects of Bulbus Allii Sativi on serum lipids and lipoproteins reviewed 25 randomized, controlled trials (published and unpublished) (116) and selected 16 with data from 952 subjects to include in the analysis. Fourteen of the trials used a parallel group design, and the remaining two were cross-over studies. Two of the studies were conducted in an openlabel fashion, two others were single-blind, and the remainder were doubleblind. The total daily dose of garlic was 600–900mg of dried garlic powder, or 10g of raw garlic, or 18 mg of garlic oil, or aged garlic extracts (dosage not stated). The median duration of the therapy was 12 weeks. Overall, the subjects receiving garlic supplementation (powder or non-powder) showed a 12% reduction (average) in total cholesterol, and a 13% reduction (powder only) in serum triglycerides. Meta-analysis of the clinical studies confirmed the lipidlowering action of garlic. However, the authors concluded that the overall quality of the clinical trials was poor and that favourable results of betterdesigned clinical studies should be available before garlic can be routinely recommended as a lipid-lowering agent. However, current available data support the hypothesis that garlic therapy is at least beneficial (116). Another metaanalysis of the controlled trials of garlic effects on total serum cholesterol reached similar conclusions (117). A systematic review of the lipid-lowering potential of a dried garlic powder preparation in eight studies with 500 subjects had similar findings (118). In seven of the eight studies reviewed, a daily dose of 600–900mg of garlic powder reduced serum cholesterol and triglyceride levels by 5–20%. The review concluded that garlic powder preparations do have lipid-lowering potential (118).
An increase in fibrinolytic activity in the serum of patients suffering from atherosclerosis was observed after administration of aqueous garlic extracts, the essential oil, and garlic powder (119, 120). Clinical studies have demonstrated that garlic activates endogenous fibrinolysis, that the effect is detectable for several hours after administration of the drug, and that the effect increases as the drug is taken regularly for several months (43, 121). Investigations of the acute haemorheological (blood flow) effect of 600–1200mg of dry garlic powder demonstrated that the drug decreased plasma viscosity, tissue plasminogen activator activity and the haematocrit level (118).
The effects of the drug on haemorheology in conjunctival vessels was determined in a randomized, placebo-controlled, double-blind, cross-over trial. Garlic powder (900 mg) significantly increased the mean diameter of the arterioles (by 4.2%) and venules (by 5.9%) as compared with controls (122). In another double-blind, placebo-controlled study, patients with stage II peripheral arterial occlusive disease were given a daily dose of 800 mg of garlic powder for 4 weeks (123, 124). Increased capillary erythrocyte flow rate and decreased plasma viscosity and plasma fibrinogen levels were observed in the group treated with the drug (123, 124). Determinations of platelet aggregation ex vivo, after ingestion of garlic and garlic preparations by humans, suffers from methodological difficulties that may account for the negative results in some studies (24). In one study in patients with hypercholesterolinaemia treated with a garlic–oil macerate for 3 months, platelet adhesion and aggregation decreased significantly (125). In a 3-year intervention study, 432 patients with myocardial infarction were treated with either an ether-extracted garlic oil (0.1mg/kg/day, corresponding to 2 g fresh garlic daily) or a placebo (126). In the group treated with garlic, there were 35% fewer new heart attacks and 45% fewer deaths than in the control group. The serum lipid concentrations of the treated patients were also reduced (126).
The acute and chronic effects of garlic on fibrinolysis and platelet aggregation in 12 healthy patients in a randomized, double-blind, placebo-controlled cross-over study were investigated (30). A daily dose of 900 mg of garlic powder for 14 days significantly increased tissue plasminogen activator activity as compared with placebo (30). Furthermore, platelet aggregation induced by adenosine diphosphate and collagen was significantly inhibited 2 and 4 hours after garlic ingestion and remained lower for 7 to 14 days after treatment (30). Another randomized, double-blind, placebo-controlled study investigated the effects of garlic on platelet aggregation in 60 subjects with increased risk of juvenile ischaemic attack (29). Daily ingestion of 800 mg of powdered garlic for 4 weeks significantly decreased the percentage of circulating platelet aggregates and spontaneous platelet aggregation as compared with the placebo group (29).
Oral administration of garlic powder (800mg/day) to 120 patients for 4 weeks in a double-blind, placebo-controlled study decreased the average blood glucose by 11.6% (30). Another study found no such activity after dosing noninsulin- dependent patients with 700 mg/day of a spray-dried garlic preparation for 1 month (127).
References:
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29. Kiesewetter H et al. Effect of garlic on platelet aggregation in patients with increased risk of juvenile ischaemic attack. European journal of clinical pharmacology, 1993, 45:333–336.
30. Kiesewetter H et al. Effect of garlic on thrombocyte aggregation, microcirculation, and other risk factors. International journal of clinical pharmacology, therapy and toxicology, 1991, 29:151–155.
32. Damrau F, Ferguson EA. The modus operandi of carminatives. Review of gastroenterology, 1949, 16:411–419.
43. Koch HP, Lawson LD, eds. Garlic, the science and therapeutic application of Allium sativum l. and related species. Baltimore, Williams and Wilkins, 1996.
113. Rashid A, Hussain M, Khan HH. Bioassay for prostaglandin-like activity of garlic extract using isolated rat fundus strip and rat colon preparation. Journal of the Pakistan Medical Association, 1986, 36:138–141.
114. Neil HA, Silagy CA. Garlic: its cardioprotectant properties. Current opinions in lipidology, 1994, 5:6–10.
115. Silagy CA, Neil A. A meta-analysis of the effect of garlic on blood pressure. Journal of hypertension, 1994, 12:463–468.
116. Silagy CA, Neil A. Garlic as a lipid lowering agent: a meta-analysis. Journal of the Royal College of Physicians of London, 1994, 28:39–45.
117. Warshafsky S, Kamer RS, Sivak SL. Effect of garlic on total serum cholesterol. A meta-analysis. Annals of internal medicine, 1993, 119:599–605.
118. Brosche T, Platt D. Garlic as a phytogenic lipid lowering drug: a review of clinical trials with standardized garlic powder preparation. Fortschritte der Medizin, 1990, 108:703–706.
119. Harenberg J, Giese C, Zimmermann R. Effects of dried garlic on blood coagulation, fibrinolysis, platelet aggregation, and serum cholesterol levels in patients with hyperlipoproteinemia. Atherosclerosis, 1988, 74:247–249.
120. Bordia A et al. Effect of essential oil of garlic on serum fibrinolytic activity in patients with coronary artery disease. Atherosclerosis, 1977, 26:379–386.
121. Chutani SK, Bordia A. The effect of fried versus raw garlic on fibrinolytic activity in man. Atherosclerosis, 1981, 38:417–421.
122. Wolf S, Reim M. Effect of garlic on conjunctival vessels: a randomised, placebocontrolled, double-blind trial. British journal of clinical practice, 1990, 44:36–39.
123. Kiesewetter H, Jung F. Beeinflusst Knoblauch die Atherosklerose? Medizinische Welt, 1991, 42:21–23.
124. Jung H, Kiesewetter H. Einfluss einer Fettbelastung auf Plasmalipide und kapillare Hautdurchblutung unter Knoblauch. Medizinische Welt, 1991, 42:14–17.
125. Bordia A. Klinische Untersuchung zur Wirksamkeit von Knoblauch. Apotheken- Magazin, 1986, 6:128–131.
126. Bordia A. Knoblauch und koronare Herzkrankheit: Wirkungen einer dreijährigen Behandlung mit Knoblauchextrakt auf die Reinfarkt- und Mortalitätsrate. Deutsche Apotheker Zeitung, 1989, 129:16–17.
127. Sitprija S et al. Garlic and diabetes mellitus phase II clinical trial. Journal of the Medical Association of Thailand, 1987, 70:223–227.
Source: WHO Monographs Vol 1, 1999 -2010
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