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Is Garlic Effective in the Lowering of LDL-Cholesterol Levels?

Ijeoma Osigwe

October 5, 2009

What is hypercholesterolemia?

            Many Americans have fallen victim to the obesity epidemic of the 21st century and its numerous consequences. Among these consequences is a health condition known as hypercholesterolemia. Hypercholesterolemia is a medical condition marked by high levels of cholesterol in the blood (http://en.wikipedia.org/wiki/Hypercholesterolemia). It is caused by abnormalities in the levels of lipoproteins, which are the particles that carry cholesterol in the bloodstream. Among the many types of lipoproteins are low-density lipoproteins (LDL) and high-density lipoproteins (HDL). Low-density lipoproteins (“bad cholesterol”) carry cholesterol from the liver to cells of the body and high-density lipoproteins (“good cholesterol”) collect cholesterol from the body’s tissues and return it to the liver (http://en.wikipedia.org/wiki/Lipoprotein). Most commonly, hypercholesterolemia refers to elevated levels of LDL- cholesterol. Irregular lipoprotein levels may be the result of the presence of other diseases, such as diabetes, or of genetic susceptibility. However, most commonly they are a result of a diet high in saturated fat combined with a lack of exercise; thus, hypercholesterolemia is most common overweight and obese individuals (http://www.umm.edu/altmed/articles/hypercholesterolemia-000084.htm). Hypercholesterolemia may contribute to the development of other diseases, most notably cardiovascular disease, which is a leading cause of death among Americans. Therefore, strategies to lower LDL-cholesterol levels are especially valuable to Americans, as well as people worldwide.  Cholesterol

Hypercholesterolemia Prevention Strategies and Treatment

            Doctors nationwide have agreed on a number of preventative strategies and treatments for hypercholesterolemia. Prevention includes eating a well- balanced diet—especially one low in saturated and trans fat—, getting regular exercise, and losing excess weight (http://www.umm.edu/altmed/articles/hypercholesterolemia-000084.htm). Treatment includes medication, specifically the prescription of statins, a class of drugs used to lower cholesterol levels, and in extreme cases surgery may be required. By combining these preventative strategies with treatment, cholesterol levels may be decreased by up to thirty percent (http://en.wikipedia.org/wiki/Hypercholesterolemia). Though these are confirmed strategies for prevention and treatment of hypercholesterolemia, many still turn to alternative strategies for a number of reasons. Medication and surgery may be very costly and dieting and exercise can be very difficult to keep up with. Thus, many often turn to less expensive, easier, experimental strategies. Among these strategies for lowering cholesterol levels is the consumption of garlic. The properties of garlic have been analyzed through a number of scientific studies in order to assess this claim.

What is significant about garlic?

            Garlic (Allium sativum) has been used medicinally all over the world for more than 5,000 years, treating a number of conditions, from hypertension to bacterial infections. Presently, it is used as an option for lowering LDL-cholesterol levels. Rahman and Lowe (2006) discuss the composition of the garlic plant as the reason for its medicinal properties; garlic, specifically the root bulb, is composed of water, sulfur compounds called thiosulfinates, amino acids, and numerous vitamins and minerals. In a study on the health effects of garlic, Tattelman (2005) suggests that one particular thiosulfinate—allicin—is the active element in garlic responsible for its numerous medicinal properties, particularly its reduction effect on LDL- cholesterol.

 

How does allicin works to reduce cholesterol levels?

            Allicin is an organosulfur compound that is released from garlic (http://en.wikipedia.org/wiki/Allicin). It is produced in a chemical reaction where the enzyme allin is converted by another enzyme, allinase, into allicin. Both of these enzymes are found naturally in garlic, as well as other species of the Allium family. The conversion occurs naturally in the garlic plant. When the garlic plant is damaged, the allinase is released to catalyze the production of allicin, which gives off a very strong, pungent odor (the “garlic smell”) as an act of defense. The same reaction occurs when garlic is, for example, cut with a knife. (http://en.wikipedia.org/wiki/Alliinase).

            Aliicin is believed to act as a natural form of statin, the class of drugs used to lower cholesterol levels (http://www.all4naturalhealth.com/garlic-to-lower-cholesterol.html). Statins works by competitively inhibiting HMG-CoA reductase, the rate- limiting enzyme for cholesterol synthesis. Statins are similar molecularly to HMG-CoA reductase, so they are able to situate themselves into the HMG-CoA reductase binding sites and replace the enzyme (http://www.medicinenet.com/statins/article.htm). This delays the reaction for the formation of cholesterol and thus, less cholesterol is produced.

 

Competitive Inhibition

Is garlic actually effective in lowering LDL- cholesterol?

            Several studies have been conducted to assess the validity of this claim. A study conducted by Gardner, Lawson, Block, and Kiazand (2007) examined the effects of raw garlic vs. commercial garlic supplements on plasma lipid concentrations in adults with moderate hypercholesterolemia. In this study, 192 adults with low- density lipoprotein cholesterol (LDL-C) were randomly assigned to 1 of 4 treatments: raw garlic, a powdered garlic supplement called Garlicin, an aged garlic extract supplement called Kyolic, or placebo. Each product was consumed six days a week for six months. Eleven blood samples were collected from each participant at different intervals of the study, and low- density lipoprotein cholesterol levels were measured by enzymatic determination of cholesterol. At the end of the study, no significant decrease in plasma lipid concentrations was noted for any of the treatments. Van Doorn, Santo, Meijer, Kamerling, and Schoemaker, (2006) examined the effect of garlic powder on C- reactive protein and plasma lipids in overweight and smoking subjects.  The study had 90 participants, all of whom were overweight, smoked greater than ten cigarettes per day, and were aged 40-75 years old. Each participant was assigned to 1 of 3 treatments: garlic tablets (2.1 grams), atorvastatin (a drug used to lower blood cholesterol; 40 mg) tablets, or placebo.  Each product was taken daily for twelve weeks. Blood samples were collected randomly throughout the twelve weeks, and after the first and third month of treatment. At the end of the study, it was found that the garlic treatment did not affect the total cholesterol level (both HDL-cholesterol and LDL- cholesterol) when compared to the placebo. However, the atorvastatin significantly reduced the total cholesterol level, especially LDL- cholesterol. Finally, Berthold, Sudhop, and von Bergmann (1998) assessed the effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism. The study included 25 patients (the mean age was 58 years old) with moderate hypercholesterolemia. Each participant was assigned to either a garlic treatment (5 mg of a steam- distilled garlic oil) or placebo. Each treatment was taken daily for 12 weeks. They were also prohibited from taking any additional garlic supplements for the duration of the study. Blood lipoprotein concentration samples were taken at the beginning and end of the study. At the end of the study, results showed that lipoprotein levels were nearly unchanged for both treatments.

Why doesn’t it work?

            There are a number of reasons why these studies yielded negative results. A review by Amagase (2006) examined the real bioactive constituents of garlic. It explains that the numerous compounds in garlic contribute to a very complex chemical structure and the preparation of garlic for its many forms alter this structure, limiting the effects of the allicin. Thus, the alteration done in the preparation of garlic powder and garlic tablets in the studies may have hindered the effect of allicin, and thus had no effect of cholesterol levels. Also, another study stated that alliinase is deactivated below a pH of 3, so allicin is generally not produced in the body from the consumption of fresh garlic (http://en.wikipedia.org/wiki/Allicin).

 

Conclusion

            Garlic is well- known for its medicinally properties and has, accordingly, been suggested as a treatment for hypercholesterolemia by lowering LDL-cholesterol levels. It was suggested that a substance found naturally in garlic called allicin is responsible for this effect. Several studies have evaluated this and have yielded similar results disproving the claim. The form of garlic used was found to limit the effectiveness of allicin; thus, it may be suggested that with proper preparation of garlic, it can be effective on lowering cholesterol. However, medication and a healthy lifestyle are the most effective treatments for hypercholesterolemia.

 

           

             

 

 

 

 

 

Web Motives

                        The websites that provided information about garlic and hypercholesterolemia were news and information sources, whose sole purpose is to inform the public. The websites are in no way affiliated with any manufacturers of garlic supplement products. The research studies that provided information about garlic and hypercholesterolemia were also news and information sources, sponsored by various medical journals. Therefore, these sources are very trustworthy and should be considered valuable knowledge. Wikipedia was also used for very basic, general information so the information obtained from it may or may not be credible.

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

 

References

Amagase, H. (2006). Clarifying the Real Bioactive Constituents of Garlic. The Journal of Nutrition, 136, 716-725.

Thomson, M., Al-Qattan, K., Bordia, T., & Ali, M. (2006). Including Garlic in the Diet May Help Lower Blood Glucose, Cholesterol, and Triglycerides. The Journal of Nutrition, 136, 800-802.

Gardner, C., Lawson, L., Block, E., Chatterjee, L., & Kiazand, A. (2007). Effect of Raw Garlic vs Commercial Garlic Supplement on Plasma Lipid Concentrations in Adults With Moderate Hypercholesterolemia. Arch Intern Med, 167, 346-353.

Rahman, K., & Lowe, G. (2006). Garlic and Cardiovascular Disease: A Critical Review. The Journal of Nutrition, 136, 736-740.

Tattelman, E. (2005). Health Effects of Garlic. American Family Physician, 72, 103-106.

van Doorn, M., Santo, S., Meijer, P., Kamerling, I., & Schoemaker, R. (2006). Effect of Garlic Powder on C-Reactive Protein and Plasma Lipids in Overweight and Smoking Subjects. The American Journal of Clinical Nutrition, 84, 1324-1329.

Berthold, H., Sudhop, T., & Lastvon Bergmann, K. (1998). Effect of a garlic oil preparation on serum lipoproteins and cholesterol metabolism: A randomized controlled trial. JAMA, 279(23), 1900-1902.

Hypercholesterolemia. Wikipedia. Retrieved (2009, October 5) from http://en.wikipedia.org/wiki/Hypercholesterolemia

Lipoprotein. Wikipedia. Retrieved (2009, October 5) from http://en.wikipedia.org/wiki/Lipoprotein(2008, December 17).

Hypercholesterolemia. Retrieved from http://www.umm.edu/altmed/articles/hypercholesterolemia-000084.htm

Allicin. Wikipedia. Retrieved (2009, October 5) from http://en.wikipedia.org/wiki/Allicin

Alliinase. Wikipedia. Retrieved (2009, October 5) from http://en.wikipedia.org/wiki/Alliinase

(2007). Garlic to lower cholesterol. Retrieved from http://www.all4naturalhealth.com/garlic-to-lower-cholesterol.html

Ogbru, Omudhome. (1996). Statins- drug class, medical uses, medication side effects, and drug interactions. Retrieved from http://www.medicinenet.com/statins/article.htm

 

 

 

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