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Cardioprotection and garlic
THE LANCET
CORRESPONDENCE Cardioprotection and garlic SIR—In his Nov 2 commentary1 Beaglehole reviews recent publications on garlic as a lipid lowering agent. In particular, he discusses the results of a recent trial from the UK that had a negative result.2 He also states that the inclusion of this and another recent negative study in a metareanalysis2 “reduced the overall estimate of the likely effect of garlic”. He fails to mention that even after inclusion of these two new trials the metareanalysis2 remained positive and concludes that “the evidence does not support use of garlic powder for cardioprotection”. I accept that, for several reasons, metaanalyses can be flawed. I doubt, however, that Beaglehole provides sufficient evidence for the above statement. First, cardioprotection entails more than lipid reduction and he hardly discusses the other cardioprotective effects of garlic (eg, ref 3). Second, the meta-analytic evidence for the lipid effects is still undeniably positive. Had Beaglehole reviewed a synthetic drug, would he have formulated his conclusions with similar strength? Could it be that we are dealing here with a textbook example of bias against complementary/alternative medicine? E Ernst Department of Complementary Medicine, Postgraduate Medical School, Exeter EX2 4NT, UK
1
2
3
Beaglehole R. Garlic for flavour, not cardioprotection. Lancet 1996; 348: 1186–87. Neil HAW, Silagy CA, Lancaster T, et al. Garlic in the treatment of moderate hyperlipidaemia: a controlled trial and a meta-analysis. J R Coll Phys 1996; 30: 329–34. Neil HAW, Silagy C. Garlic: its cardioprotective properties. Curr Opin Lipidol 1994; 5: 6–10.
SIR—Although it is true that garlic is one of the world’s most ancient medicines and has been used for many medical indications, it is only recently that the scientific community has taken it seriously and started to conduct proper clinical trials. Beaglehole1 mentions some of these studies and ignores others. Several well planned studies have indicated that garlic may have a role in cardioprotection. Garlic has been shown to inhibit cholesterol biosynthesis in hepatocytes and liver homogenates.2 Beaglehole cites Jain and
Vol 349 • January 11, 1997
colleagues’3 controlled clinical trial in which garlic reduced serum lipid concentrations. In support of these findings Harenberg and colleagues4 reported that garlic reduced serum cholesterol concentrations by 10% in patients with hyperlipoproteinaemia. Garlic also reduced systolic and diastolic blood pressure in these patients, but platelet aggregation was not affected. Recent data from Ali and Thomson5 confirmed the serum cholesterol reduction by garlic, and more importantly an 80% reduction in serum thromboxane concentrations. Another important property of garlic that Beaglehole does not mention is its antiplatelet aggregation properties. It has been known for some time that garlic decreases platelet aggregation thus inhibiting some aspects of thrombus formation. Several well conducted studies have confirmed garlic’s ability to inhibit platelet aggregation thus reducing the frequency of thrombus formation. We have seen similar antiplatelet aggregation properties of a garlic preparation in our laboratory and are conducting a small clinical trial whose results will be reported later. Many well planned studies are showing that garlic has cardioprotective properties. Standard solutions of garlic and its extracts are now available, and more basic research and clinical trials are needed to test them. Thus, in our opinion the jury is still deliberating on garlic. *Khalid Rahman, David Billington, Gaynor Rigby School of BIomolecular Sciences, Liverpool John Moores University, Liverpool L3 3AF, UK
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3
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5
Beaglehole R. Garlic for flavour, not cardioprotection. Lancet 1996; 348: 1186–87. Yeh YY, Yeh SM. Garlic reduces plasmalipids by inhibiting hepatic cholesterol and triacylglycerol synthesis. Lipids 1994; 29: 189–93. Jain AK, Vargas R, Gotzkowsky S, et al. Can garlic reduce levels of serum lipids? A controlled clinical study. Am J Med 1993; 94: 632–35. Harenberg J, Giese C, Zimmermann R. Effect of dried garlic on blood coagulation, fibrinolysis, platelet aggregation and serum cholesterol levels in patients with hyperlipoproteinemia. Atherosclerosis 1988; 74: 247–49. Ali M, Thomson M. Consumption of a garlic clove a day could be beneficial in preventing thombosis. Prostagland Leukotr Essent Fatty Acids 1995; 53: 211–12.
Author’s reply SIR—Ernst implies that a positive metaanalysis is grounds for supporting the use of garlic for lipid lowering. The potential limitations of meta-analyses are well illustrated by publications about garlic. In particular, there is evidence of publication bias with positive studies more likely to be published than negative studies.1 A positive meta-analysis is thus not sufficient to support garlic as a lipidlowering agent since it is based on a biased selection of studies. The data on the other potential cardioprotective effects of garlic are even less convincing.2 More clinical trials are justified and I encourage Rahman and colleagues to ensure that their “small” trial is well designed and has the appropriate sample size. Robert Beaglehole Faculty of Medicine and Health Sciences, University of Auckland, Private Bag B2019, Auckland, New Z ealand
1
2
Neil HAW, Silagy CA, Lancaster T, et al. Garlic in the treatment of moderate hyperlipidaemia: a controlled trial and metaanalysis. J R Coll Phys 1996; 30: 329–34. Neil HAW, Silagy C. Garlic: its cardioprotective properties. Curr Opin Lipidol 1994; 5: 6–10.
S IR —The use of natural and complementary medicine is increasing in popularity in the western world. Two decades ago it was thought by mainstream medicine to be a fringe activity with little relevance to medical practice. Today every medical practitioner has patients who are using some aspect of natural and complementary medicine. Estimates are that one in three American adults use some form of non-conventional therapy1 and one in two Australians alternative medicine.2 These figures suggest that, far from being a fringe activity, natural and complementary medicine has become an important component of public health care. Against this background, it is essential that the medical and health care communities develop rigour in their understanding and definition of natural products. In medicine definitions are precise and care is taken (usually) not to generalise beyond the boundaries of evidence. Discussion of natural products in medical journals
131
CORRESPONDENCE Cardioprotection and garlic SIR—In his Nov 2 commentary1 Beaglehole reviews recent publications on garlic as a lipid lowering agent. In particular, he discusses the results of a recent trial from the UK that had a negative result.2 He also states that the inclusion of this and another recent negative study in a metareanalysis2 “reduced the overall estimate of the likely effect of garlic”. He fails to mention that even after inclusion of these two new trials the metareanalysis2 remained positive and concludes that “the evidence does not support use of garlic powder for cardioprotection”. I accept that, for several reasons, metaanalyses can be flawed. I doubt, however, that Beaglehole provides sufficient evidence for the above statement. First, cardioprotection entails more than lipid reduction and he hardly discusses the other cardioprotective effects of garlic (eg, ref 3). Second, the meta-analytic evidence for the lipid effects is still undeniably positive. Had Beaglehole reviewed a synthetic drug, would he have formulated his conclusions with similar strength? Could it be that we are dealing here with a textbook example of bias against complementary/alternative medicine? E Ernst Department of Complementary Medicine, Postgraduate Medical School, Exeter EX2 4NT, UK
1
2
3
Beaglehole R. Garlic for flavour, not cardioprotection. Lancet 1996; 348: 1186–87. Neil HAW, Silagy CA, Lancaster T, et al. Garlic in the treatment of moderate hyperlipidaemia: a controlled trial and a meta-analysis. J R Coll Phys 1996; 30: 329–34. Neil HAW, Silagy C. Garlic: its cardioprotective properties. Curr Opin Lipidol 1994; 5: 6–10.
SIR—Although it is true that garlic is one of the world’s most ancient medicines and has been used for many medical indications, it is only recently that the scientific community has taken it seriously and started to conduct proper clinical trials. Beaglehole1 mentions some of these studies and ignores others. Several well planned studies have indicated that garlic may have a role in cardioprotection. Garlic has been shown to inhibit cholesterol biosynthesis in hepatocytes and liver homogenates.2 Beaglehole cites Jain and
Vol 349 • January 11, 1997
colleagues’3 controlled clinical trial in which garlic reduced serum lipid concentrations. In support of these findings Harenberg and colleagues4 reported that garlic reduced serum cholesterol concentrations by 10% in patients with hyperlipoproteinaemia. Garlic also reduced systolic and diastolic blood pressure in these patients, but platelet aggregation was not affected. Recent data from Ali and Thomson5 confirmed the serum cholesterol reduction by garlic, and more importantly an 80% reduction in serum thromboxane concentrations. Another important property of garlic that Beaglehole does not mention is its antiplatelet aggregation properties. It has been known for some time that garlic decreases platelet aggregation thus inhibiting some aspects of thrombus formation. Several well conducted studies have confirmed garlic’s ability to inhibit platelet aggregation thus reducing the frequency of thrombus formation. We have seen similar antiplatelet aggregation properties of a garlic preparation in our laboratory and are conducting a small clinical trial whose results will be reported later. Many well planned studies are showing that garlic has cardioprotective properties. Standard solutions of garlic and its extracts are now available, and more basic research and clinical trials are needed to test them. Thus, in our opinion the jury is still deliberating on garlic. *Khalid Rahman, David Billington, Gaynor Rigby School of BIomolecular Sciences, Liverpool John Moores University, Liverpool L3 3AF, UK
1
2
3
4
5
Beaglehole R. Garlic for flavour, not cardioprotection. Lancet 1996; 348: 1186–87. Yeh YY, Yeh SM. Garlic reduces plasmalipids by inhibiting hepatic cholesterol and triacylglycerol synthesis. Lipids 1994; 29: 189–93. Jain AK, Vargas R, Gotzkowsky S, et al. Can garlic reduce levels of serum lipids? A controlled clinical study. Am J Med 1993; 94: 632–35. Harenberg J, Giese C, Zimmermann R. Effect of dried garlic on blood coagulation, fibrinolysis, platelet aggregation and serum cholesterol levels in patients with hyperlipoproteinemia. Atherosclerosis 1988; 74: 247–49. Ali M, Thomson M. Consumption of a garlic clove a day could be beneficial in preventing thombosis. Prostagland Leukotr Essent Fatty Acids 1995; 53: 211–12.
Author’s reply SIR—Ernst implies that a positive metaanalysis is grounds for supporting the use of garlic for lipid lowering. The potential limitations of meta-analyses are well illustrated by publications about garlic. In particular, there is evidence of publication bias with positive studies more likely to be published than negative studies.1 A positive meta-analysis is thus not sufficient to support garlic as a lipidlowering agent since it is based on a biased selection of studies. The data on the other potential cardioprotective effects of garlic are even less convincing.2 More clinical trials are justified and I encourage Rahman and colleagues to ensure that their “small” trial is well designed and has the appropriate sample size. Robert Beaglehole Faculty of Medicine and Health Sciences, University of Auckland, Private Bag B2019, Auckland, New Z ealand
1
2
Neil HAW, Silagy CA, Lancaster T, et al. Garlic in the treatment of moderate hyperlipidaemia: a controlled trial and metaanalysis. J R Coll Phys 1996; 30: 329–34. Neil HAW, Silagy C. Garlic: its cardioprotective properties. Curr Opin Lipidol 1994; 5: 6–10.
S IR —The use of natural and complementary medicine is increasing in popularity in the western world. Two decades ago it was thought by mainstream medicine to be a fringe activity with little relevance to medical practice. Today every medical practitioner has patients who are using some aspect of natural and complementary medicine. Estimates are that one in three American adults use some form of non-conventional therapy1 and one in two Australians alternative medicine.2 These figures suggest that, far from being a fringe activity, natural and complementary medicine has become an important component of public health care. Against this background, it is essential that the medical and health care communities develop rigour in their understanding and definition of natural products. In medicine definitions are precise and care is taken (usually) not to generalise beyond the boundaries of evidence. Discussion of natural products in medical journals
131