Garlic, Allium sativum L., is a plant known since ancient times. The focus of medical use of garlic preparations recently shifted from neuroprotective applications to indications related to serum lipids and risk factors of CHD.
Garlic, Allium sativum L., is a spice and medicinal plant of the lily family (Fig. 1) that has been used since ancient times. Its original home is in Central and South Asia and reached Europe in ancient times.
Already the Talmud and De materia medica by Dioscurides describe the positive effect of garlic. Used, both as a spice in the kitchen and for medicinal purposes, have always been the onions, called garlic cloves (Fig. 2). In the kitchen they are freshly squeezed, in medicine dried and powdered or used as an extract.
For centuries, garlic was also associated with superstition. Garlic cloves tied together were worn as talismans to protect against contagious diseases and hung to ward off vampires and ghosts.
Ingredients
Fresh garlic contains 0.5 to 1% alliin, an amino acid which is converted into the non-stable allicin when the cell structures are destroyed (Fig. 3). Allicin gives rise to di- and trisulfides, which are responsible for the typical garlic odor. However, this does not come from the stomach after eating garlic, but is released into the air we breathe via the alveoli. Milk or chlorophyll should neutralize some of the sulfur compounds from the air we breathe. However, some of the di- and trisulfides are also excreted through the skin.
The term “aged black garlic”, which is particularly popular in the USA, refers to a processed garlic originating from Asia. In this process, garlic cloves are exposed to high temperature for 30 days. The garlic turns dark and has a pleasant taste. In the studies presented below, this “aged black garlic” was used in part.
Effectiveness
Garlic preparations used to be very widely used to improve brain performance such as for memory and concentration, as well as against heart problems. Corresponding preparations were often combinations of garlic and hawthorn. Towards the end of the last century, the triumphal march of Ginkgo biloba began, which then soon outstripped garlic preparations for the prevention of cognitive disorders.
The scientific knowledge about the antiarteriosclerotic properties of garlic preparations was obtained in pharmacological animal studies. A review of these was presented in 2007 at the 22nd Swiss Conference on Phytotherapy in Baden [1]. However, there are other applications of garlic, some of which have been clinically confirmed. These include, for example, the positive effect on blood lipids. In recent years, several clinical studies have been published that addressed this issue:
Lipid Studies
RCT 2008: In 2008, Sobenin et al. a randomized, placebo-controlled, double-blind study of the effect of garlic on lipids [2]. In this study, 42 men aged 35-70 years who had mild hypercholesterolemia took 600 mg of garlic powder daily for 12 weeks. Total cholesterol decreased significantly in the verum group compared to baseline and to placebo. (Baseline: p=0.004, Placebo: p=0.005). The decrease in LDL and the increase in HDL also reached significance.
Meta-analysis 2009: Meta-analyses have also been published, two with a positive [3,4] and one with a negative result [5].
In the 2009 meta-analysis [3], the authors searched for randomized controlled trials (RCTs) that examined the effect of garlic on total cholesterol, triglycerides, LDL, and HDL. 29 identified studies were reviewed and showed that garlic significantly reduced total cholesterol as well as triglycerides, but had no effect on LDL and HDL. According to the authors, there was moderate statistical heterogeneity in the analysis.
Meta-analysis 2013: Another meta-analysis published in 2013 [4] came to a similar but slightly differentiated result: this time, the authors evaluated 39 studies and determined in subjects with a total cholesterol level of >200 mg/dl and a garlic intake of >2 months, a reduction in total cholesterol of 17± 6 mg/dl (8%) and a reduction in LDL of 9±6 mg/dl. The authors pointed to the fact that this 8% reduction in total cholesterol in 50-year-olds reduces the risk of coronary events by 38%. This meta-analysis, in contrast to the 2009 meta-analysis, did not identify any improvement in triglyceride levels.
Negative meta-analysis 2009: In the same year as the meta-analysis by Reinhard et al. [3], another meta-analysis [5] appeared with a negative result. Koo and Aziz evaluated 13 studies but found no improvement in serum lipid levels with garlic ingestion. It is striking that only 13 studies were evaluated in this meta-analysis, whereas 29 studies were evaluated in the other meta-analysis published in the same year with a positive result. Again, moderate to high heterogeneity was found between studies.
RCT 2014: A randomized, double-blind, placebo-controlled trial appeared again in 2014 [6], in which 55 subjects with mild hypercholesterolemia received either 3 g of garlic powder (n=28) or placebo (n=27) twice daily for 12 weeks. This study again yielded new results: No different concentrations of total cholesterol, triglycerides, and LDL were found in serum lipids between the verum and placebo groups. In contrast, the researchers found that the level of HDL increased in the verum group, and they also detected a significant decrease in the concentration of alipoprotein B and a significant increase in the ratio of LDL and alipoprotein.
Cardioprotective properties
Finally, two reviews and one RCT on cardioprotective properties of garlic [7–9] have also been published in recent years. These attribute positive properties to garlic in hypertension as well as in risk factors of CHD. However, because of the heterogeneity of the studies evaluated, the authors point to the need for further studies.
Summary
Garlic, Allium sativum L., is a plant known and described since ancient times, the bulb of which is used both in cooking and medicine, and in earlier times was also associated with superstition.
The medical use of garlic preparations and powders shifted in the last 20 to 30 years from neuroprotective applications to improve memory and focus on indications related to serum lipids and other risk factors of CHD, incl. Hypertension.
From a critical point of view with regard to complementary medicine applications, the heterogeneity of the presented studies could be pointed out. For example, in the studies on serum lipids, improvement in other values was found in each individual.
Another problem lies in the fact that although several preparations containing a defined amount of garlic are on the market in Switzerland (box), only one is available as a monopreparation (Vogel garlic capsules). None of the preparations is reimbursed by the basic insurance, only by the supplementary insurance in each case.
It is the responsibility of the attending physician to recommend that garlic therapy be attempted in the case of serum lipids moderately deviating from the norm or hypertension prior to prescribing statins and/or antihypertensives.
Literature:
- Schulz V: Garlic – artichoke – turmeric and lipid metabolism: paper presented at the 22nd Swiss Conference on Phytotherapy, Baden, 29.11.2007, published in Phytotherapy 2008 (1/2); 8: 19-22.
- Sobenin LA, et al: Lipid-lowering effects of time-released garlic powder tablets in double-blinded placebo-controlled randomized study. J Atheroscler Thromb 2008; 15(6): 334-338.
- Reinhard KM, et al: The impact of garlic on lipid parameters; a systematic review and meta-analysis. Nutr Res Rev 2009; 22(1): 39-48.
- Ried K, et al: Effect of garlic on serum lipids: an updated meta-analysis. Nutr Rev 2013; 71(5): 282-299.
- Koo YS, Aziz Z: Garlic supplementation and serum cholesterol: a meta-analysis. J Clin Pharm Ther 2009; 34(2): 133-145.
- Jung ES, et al: Reduction of blood lipid parameters by a 12-wk supplementation of aged black garlic: a randomized controll trial. Nutrition 2014; 30(9): 1034-1039.
- Schwinghackl L, et al: An umbrella review of garlic intakte and risk of cardiovascular disease. Phytomedicine 2016; 23(11): 1127-1133.
- Varshnev R, Budoff MJ: Garlic and Heart Disease. J Nutr 2016; 146(2): 416S-421S.
- Ried K, et al: The effect of aged garlic extract on blood pressure and other cardiovascular risk factors in uncontrolled hypertensives: the AGE at Heart trial. Integr Blood Press Control 2016; 9: 9-21.
HAUSARZT PRAXIS 2018; 13(1): 6-7
