Allium sativum: Garlic and Cardiovascular Disease

by Paul Bergner

Medical Herbalism 01-31-95 6(4): 1, 4-5

It’s not news that garlic is an important herb for the cardiovascular system. It’s news, however, when its effects for lowering blood pressure and cholesterol begin to receive wide coverage in conventional medical journals, with suggestions that it can be used in some cases instead of pharmaceutical drugs. That’s what has happened in 1994.

Many garlic trials have appeared in the scientific literature in recent years, but most have been flawed from a scientific point of view — poor trial design, lack of controls, or small numbers of participants. Many of these trials were sponsored by companies selling garlic products. What occurred last year is that some conventional researchers reviewed all the research with meta-analyses — pooling the data from many trials to solve the problem of small numbers in any one trial. In each case, the researchers discarded data from uncontrolled trials and trials that did not last long enough.

Garlic and hypertension

One meta-analysis pooled the data from 415 patients from eight controlled trials of garlic for high blood pressure (Sigaly and Neal; 1994b). It only included trials that were at least four weeks in duration. A typical drop was 7.7 mm Hg systolic and 5 mm diastolic. This is a mild lowering, with typical doses of 600-900 mg garlic powder per day for twelve weeks, and does not match the effects of blood-pressure-lowering drugs. Normal blood pressure is less than 140/90. Severe hypertension is greater than 180/115. Most hypertension cases are mild or moderate, falling between those two levels. Thus garlic at this dose would only correct mild hypertension. Higher doses of garlic may be more effective, however. One trial (not included in the meta-analysis), noted blood-pressure-lowering effects, including a 16 mm drop in diastolic pressure five hours after administering 2400 mg of garlic. The patients in that trial had severe hypertension (DBP 115 mm Hg) (McMahon et al). Doses as high as 10 grams per day of fresh garlic have been given in other garlic trials (not hypertension trials) (Gadkari and Joshi). Even if garlic will not do the whole job of lowering blood pressure, it certainly has earned a place with other lifestyle changes affecting blood pressure — exercise, weight loss, low-fat diet, salt restriction, supplementation with calcium, magnesium, and potassium, EPA, stress reduction, and cessation of smoking, alcohol and caffeine.

Cholesterol-lowering effects

The same authors did a meta-analysis of garlic trials for lowering cholesterol, and found even more striking results (Sigaly and Neal 1994a.) They collected data on 952 patients from sixteen trials, and found an average of 12% reduction in cholesterol, evident after one month. Best results were with trials lasting at least three months. The typical dose was the equivalent of 600-900 mg of garlic powder. Garlic powder, fresh garlic, garlic extract, or garlic oil were all used in the various trials. An earlier meta-analysis from 1993 suggested that garlic, in an amount approximating one-half to one clove per day, decreases total serum cholesterol levels by about 9% (Warshafsky et al). Several trials (not included in the meta-analysis) note that garlic also may lower triglycerides and raise HDL-cholesterol (the “good” cholesterol) (Rotzsh et al).
 

Preventing atherosclerotic disease

In one animal trial, researchers demonstrated that garlic not only lowers cholesterol, but that it can actually prevent atherosclerosis, which is the reason for lowering cholesterol in the first place (Mirhadi et al). In the current model of atherosclerotic disease, such as heart attack or stroke, “thick” blood running through cholesterol-narrowed arteries forms a clot. Oxidized LDL cholesterol appears to be the culprit in fatty deposits in the arteries, which is why antioxidants are so important in preventing atherosclerosis. The risk of atherosclerotic disease can be reduced either by “thinning” the blood (making it less likely to clot) or by preventing the narrowing of the arterial passage. It is the blood-thinning properties of aspirin that have earned it a place in conventional medicine for the prevention of heart attacks. Garlic apparently does both, i.e. it reduces clotting and lowers the cholesterol that build the deposits that narrow the walls. Garlic appears to lower cholesterol by reducing the production of it in the liver. It also inhibits the production of fatty acids there (Yeh and Yeh; Gebhardt; Heinle and Betz).

A number of trials demonstrate garlic’s blood-thinning properties(Elwood et al; Gadkari and Joshi; Kiesewetter et al, 1991; Kiesewetter et al, 1993). The clinical importance of this thinning was shown in a clinical trial in patients with intermittent claudication. In this condition, associated with atherosclerosis, pain in the buttocks or legs is caused by reduced blood flow due to narrowed arteries. Garlic significantly improved the maximum walking distance in patients with claudication. The authors point out that the effects started after about five weeks of administration, and that they corresponded to a simultaneous thinning of the blood at that time. It appears that the thinner blood was better able to circulate through the narrowed arteries (Keisewetter et al, 1993).

Side effects and patient compliance

None of the trials noted side effects, and apparently none of the patients complained about the odor of garlic. However, this does not mean that all patients will comply with a regimen of garlic. Patients often do not tell their doctors — even researchers — their concerns, and garlic has a wide reputation as an anti-social food. It may take some work with the individual patient to see whether they will take supplements, introduce garlic into their diet, or take fresh garlic. One trial noted above got participants to take ten grams of fresh garlic a day for several months by taking it after the morning meal.

Traditional herbalism describes some other difficulties that may arise with garlic. Seventeenth century herbal giant Nicholas Culpepper praised the virtues of garlic for a wide variety of conditions — mainly antibacterial. He also gave a word of caution:

Authors quote many other diseases this is good for, but conceal its vices. Its heat is very vehement; and all vehement hot things send up the ill-savored vapors to the brain. In choleric men it will add fuel to the fire; in men oppressed by melancholy it will attenuate the humor, and send up strong fancies, and as many strange visions to the head; therefore let it be taken internally with great moderation; outwardly you may be more bold with it.

Culpepper was the last great Western herbalist to practice according to the “four humors” system of the greeks, Galen, and the Arabs. The choleric constitution, described above, is hot and dry. Melancholic states are cold and dry. The common factor is dryness, and it might be generalized that garlic should be used with caution in patients with a tendency to dehydration, whether hot or cold. I have seen garlic aggravate a case of rheumatoid arthritis (a hot condition) when taken internally, and severely irritate the ear after topical application in an infant with otitis media (middle ear infection).

We are probably emerging from the historical era of “wonder drugs” as the wonder is wearing off much of modern medicine. At the same time we are entering a period of “wonder-herbs,” with the wonder coming from the fact some simple plants are more effective than drugs and do not have their side effects. Garlic, by combining blood-pressure-lowering, cholesterol-lowering, atherosclerosis-prevention, and blood-thinning, combines the properties of at least three major allopathic drugs, without any of their side effects. Furthermore, several studies have shown that the use of cholesterol-lowering drugs, although leading to lower deaths from atherosclerotic disease, actually increase the overall death rate (Davey Smith). If this is true then garlic is certainly preferable to these drugs.

References

Davey Smith G, Song F, Sheldon TA. “Cholesterol lowering and mortality: the importance of considering initial level of risk,” BMJ 1993;306:1367-73

Elwood PC, Beswick AD, O’Brien JR, Yarnell JW, Layzell JC, Limb ES. “Inter-relationships between haemostatic tests and the effects of some dietary determinants in the Caerphilly cohort of older men.” Blood Coagul Fibrinolysis 1993 Aug;4(4):529-36

Gadkari JV, Joshi VD. “Effect of ingestion of raw garlic on serum cholesterol level, clotting time and fibrinolytic activity in normal subjects.” J Postgrad Med 1991 Jul;37(3):128-31

Gebhardt R. “Multiple inhibitory effects of garlic extracts on cholesterol biosynthesis in hepatocytes.” Lipids (1993)Jul;28(7):613-9

Heinle H, Betz E. “Effects of dietary garlic supplementation in a rat model of atherosclerosis.” Arzneimittelforschung 1994 May;44(5):614-7

Kiesewetter H, Jung F, Jung EM, Blume J, Mrowietz C, Birk A, Koscielny J, Wenzel E, “Effects of garlic coated tablets in peripheral arterial occlusive disease.” Clin Investig 1993 May;71(5):383-6

Kiesewetter H, Jung F, Pindur G, Jung EM, Mrowietz C, Wenzel E “Effect of garlic on thrombocyte aggregation, microcirculation, and other risk factors.” Int J Clin Pharmacol Ther Toxicol 1991 Apr;29(4):151-5

McMahon FG, Vargas R. “Can garlic lower blood pressure? A pilot study.” Pharmacotherapy 1993 Jul-Aug;13(4):406-7

Mirhadi SA, Singh S, Gupta PP. “Effect of garlic supplementation to cholesterol-rich diet on development of atherosclerosis in rabbits.” Indian J Exp Biol 1991 Feb;29(2):162-8

Rotzsch W, Richter V, Rassoul F, Walper A. “Postprandial lipemia under treatment with Allium sativum. Controlled double-blind study of subjects with reduced HDL2-cholesterol.” Arzneimittelforschung 1992 Oct;42(10):1223-7

Silagy C, Neil A. “Garlic as a lipid lowering agent — a meta-analysis.” J R Coll Physicians Lond 1994 Jan-Feb;28(1):39-45

Silagy CA, Neil HA. “A meta-analysis of the effect of garlic on blood pressure.” J Hypertens 1994 Apr;12(4):463-8

Warshafsky S, Kamer RS, Sivak SL, “Effect of garlic on total serum cholesterol. A meta-analysis. Ann Intern Med 1993 Oct 1;119(7 Pt 1):599-605

Yeh YY, Yeh SM, “Garlic reduces plasma lipids by inhibiting hepatic cholesterol and triacylglycerol synthesis.” Lipids 1994 Mar;29(3):189-93
  Copyright 2001 Paul Bergner




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