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Its Bad For Your Breath And Good For Cholesterol

Garlic may have a pungent odor and cause bad breath but it is good for you. Besides its culinary uses, this plant from the onion family is rich in bioactive sulfur compounds that have been shown to lower blood cholesterol. What are these cholesterol-lowering sulfur compounds and how can you take garlic to reduce blood cholesterol? Read on to find out how garlic affects the absorption, metabolism and excretion of cholesterol as well as its other cardiovascular benefits.
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What is Garlic?

Garlic or Allium sativum belongs in the larger onion plant family. It is native to Asia but also commonly grown in the Mediterranean regions of Africa and Europe.

Garlic is used in food preparation as seasoning or condiment. It impacts a pungent flavor especially when the bulb is used. Besides the bulb, other edible parts of garlic include the leaves and flowers. Bulb garlic is sold fresh, frozen, dried or fermented. In addition, garlic can be powdered for use in food preparation or as herbal medicine.

Raw garlic has a high nutritional value. It is rich in dietary fiber, B vitamins especially vitamin B6, vitamin C, calcium, iron, manganese, phosphorus, zinc and selenium.

Besides these nutrients, garlic is also rich in sulfur-containing compounds.

These compounds are released and broken down once the bulb is crushed. Because they are stored in the fluids of the cells, chopping, crushing or chewing damages these cells and releases the enzymes responsible for breaking down these sulfur compounds.

The compounds produced from the enzymatic breakdown of these sulfur compounds are responsible for the sharp taste and strong smell of garlic.

Sulfur Compounds of Garlic
  • Allicin
  • Alliin
  • Ajoene
  • S-allylcysteine
  • Vinyldithiins
  • Diallyl polysulfides

Health Benefits of Garlic

Garlic has antibacterial, antifungal and antiviral activities. These medicinal properties make garlic ideal for the treatment of thrush, respiratory tract infection and digestive problems. In addition, garlic can be used as an antiseptic and disinfectant.

There is also strong clinical evidence supporting the traditional use of garlic in the treatment of cough and common cold.

Furthermore, garlic has also been shown to reduce platelet aggregation and blood cholesterol level.

In addition, a number of studies indicate that garlic prevent the hardening of the arteries. Therefore, garlic can prevent atherosclerosis and the accumulation of cholesterol in the body.

Preliminary studies also indicate that garlic can help control blood sugar and prevent some complications of diabetes mellitus. Specifically, long-term garlic supplementation can reduce homocysteine levels and reduce oxidative stress in the pancreas.

Garlic also contributes to the nutritional balance of the body. It is known to be effective in the treatment and prevention of scurvy because of its high vitamin C content.

In addition, garlic increases the absorption of vitamin B1 or thiamine. Therefore, it can help prevent beriberi by enhancing the absorption of thiamine from foods.

Even though studies show that garlic can be effective in the treatment of certain disorders, high doses of garlic supplements are not recommended.

In addition, garlic used in oral preparations such as mouthwash can cause halitosis or bad breath.

Garlic and Cholesterol

The results of studies done to investigate the cholesterol-lowering properties of garlic are conflicting. While some studies find clear benefits, others found no benefits at all. However, everyone agrees that garlic has cardiovascular benefits beyond simply affecting cholesterol levels.

The major study often quoted in the argument against the hypocholesterolemic benefits of garlic was published in the Archives of Internal Medicine in 2007. This clinical trial was funded by the National Institutes of Health and involved 192 adults with moderate hypercholesterolemia.

The participants were divided into 4 groups. While the control group was given placebo, the other groups got 3 different forms of garlic: raw garlic (in sandwich), powdered garlic supplement and aged garlic extract supplement.

All 3 garlic preparations contained substantial amounts of allicin, the sulfur compound believed to be responsible for the cholesterol-lowering property of garlic.

The participants received these treatments for 6 days every week throughout the 6-month duration of the study. Their blood cholesterol levels were measured every month during the study.

The results showed that garlic supplementation did not improve lipid profile at all during the study.

While this study demonstrated that garlic did not reduce cholesterol levels, some experts pointed out that the results did not actually confirm this conclusion. They argue that it is possible that the doses of garlic (or allicin) used in the study were too low to affect blood cholesterol levels.

In addition, some experts suggested that the cholesterol-lowering effect of garlic may only be beneficial for those suffering from severe hypercholesterolemia.

In fact, a 2012 meta-analysis of randomized, placebo-controlled, double-blind studies done on the subject showed that garlic supplementation can lower total serum cholesterol and triglyceride levels.

How Garlic Affects Cholesterol Levels

Garlic supplementation

  • Significantly lowers total cholesterol level
  • Modestly lowers LDL (low-density lipoprotein or “bad”) cholesterol level
  • Does not affect HDL (high-density lipoprotein or “good”) cholesterol level
  • Significantly lowers triglyceride levels

Studies on Garlic and Cholesterol

Negative Studies

A 2009 meta-analysis published in the Journal of Clinical Pharmacy and Therapeutics concluded that the results of available randomized, controlled studies did not demonstrate the cholesterol-lowering effects of garlic.

The reviewers included 13 studies involving 1056 participants in total from different clinical research databases.

Even though they concluded that the studies did not support garlic supplementation in the treatment of hypercholesterolemia, they agreed that the studies they used were too flawed to reach a definite conclusion on the effect of garlic on serum cholesterol.

A 1996 meta-analysis published in the Journal of the Royal College of Physicians of London also reached similar conclusions.

In that study, the researchers gave a group of patients with high-cholesterol levels 300 mg of dried garlic tablet (containing 1.3% allicin) 3 times daily for 6 months. At the end of the study, the researchers found no difference (in cholesterol levels) between the garlic group and the placebo group.

Similarly, a 1998 study published in The Journal of the American Medical Association concluded that garlic oil had no effect on lipoproteins and cholesterol metabolism.

The researchers obtained this result from giving 5 mg of steam-distilled garlic oil preparation twice daily for 12 weeks to 25 adults with moderate hypercholesterolemia.

Some experts have argued that the preparation, type and dose of garlic extract used determine the cholesterol-lowering effect of garlic preparations.

While these negative studies may use garlic extracts with standardized allicin content, there is a valid concern over the release of allicin from such extracts. For example, it is unlikely that the allicin content of garlic oil preparation is high. In addition, the oil preparation may not serve as an ideal vehicle for allicin and may, therefore reduce the bioavailability of the sulfur compounds in garlic.

There are just as many studies and reviews that find evidence to support the cholesterol-lowering potential of garlic as there are clinical trials that find no such evidence.

Positive Studies

Another meta-analysis done in 2009 and published in the journal, Nutrition Research Reviews, reached a conclusion very different from the one published in the Journal of Clinical Pharmacy and Therapeutics even though both reviews pooled studies from the same research databases.

This review concluded that garlic modestly reduced total cholesterol and triglyceride levels even though it has no effect on the levels of HDL and LDL cholesterol.

Yet another meta-analysis of past studies published in the Annals of Internal Medicine in 2000 found that garlic modestly lowered total cholesterol, triglyceride and LDL cholesterol levels.

A 1990 German study published in the journal, Arzneimittel-forschung, is important because it is one of the very few large, multicenter studies done to investigate the cholesterol-lowering effect of garlic.

The placebo-controlled, randomized study involved 261 patients with hypercholesterolemia from 30 different medical centers in Germany. The treatment group was given 800 mg standardized garlic powder tablets (standardized to 1.3% alliin equivalent to 0.6% allicin) for 4 months.

The results of the study showed that garlic reduced the levels of total cholesterol by 12% and triglyceride by 17%.

One of the recent studies supporting the use of garlic for lowering cholesterol levels was published in the journal, Oxidative Medicine and Cellular Longevity, in 2012.

In that study, the researchers fed different doses (5 mg/kg, 10 mg/kg and 20 mg/kg) of allicin to a group of mice for 12 weeks. After the treatment duration, the results showed that all 3 doses of allicin lowered blood cholesterol, liver cholesterol, triglycerides and glucose levels.

The reduction in cholesterol, triglycerides and glucose levels depended on the dose of allicin administered with the highest dose producing the best result.

How Garlic Lowers Cholesterol Levels

A 2001 study published in the Journal of Nutrition provided great insight into how garlic lowers cholesterol levels and also identified the bioactive phytochemicals responsible for this effect.

The authors of the study gathered information from different studies to determine that aged garlic extract was effective for reducing total cholesterol, LDL cholesterol and triglyceride levels in human and animal studies.

In addition, the authors found that experiments with rat liver cells showed that both water-soluble and lipid-soluble extracts of garlic can lower cholesterol levels.

Cholesterol-lowering Phytochemicals of Garlic

Water-Soluble Compounds

  • S-allylcysteine
  • S-ethylcysteine
  • S-propylcysteine
  • Gamma-glutamyl-S-allylcysteine
  • Gamma-glutamyl-S-methylcysteine
  • Gamma-glutamyl-S-propylcysteine

The cholesterol-lowering effect of the first 3 compounds is twice that of the latter 3 compounds and 4 times the cholesterol-lowering effect of the lipid-soluble compounds.

Lipid-Soluble Compounds

  • Diallyl sulfide
  • Diallyl disulfide
  • Diallyl trisulfide
  • Dipropyl sulfide
  • Dipropyl trisulfide

The summary of their findings is detailed below.

  • Water-soluble sulfur compounds produce a greater reduction in cholesterol levels than lipid-soluble sulfur compounds
  • Water-soluble sulfur compounds are generally not toxic even at high concentration (the exception is S-allylmercaptocysteine)
  • One mechanism by which garlic reduces cholesterol by inhibiting its synthesis in the liver. The water-soluble compounds especially S-allylcysteine act by this mechanism

A 1993 study published in the journal, Lipids, provided an in-depth look into the processes involved in mechanism by which water-soluble garlic compounds inhibit cholesterol synthesis.

The researcher exposed rat and human liver cell lines to these water-soluble compounds and determined that the inhibition of cholesterol synthesis depended on the doses of these compounds.

At low doses, garlic inhibits the enzyme, HMG-CoA reductase, and acts a lot like statins.

However, at high doses, garlic not only blocks HMG-CoA reductase but also other enzymes involved in the syntheses of the precursors of cholesterol.

The researcher found out that garlic recruits nicotinic acid and adenosine for the inhibition of cholesterol synthesis when given in low doses. At high concentrations, allicin is involved in the inhibition of cholesterol precursors.

Alliin, the major sulfur-containing compound in garlic, had no effect and was only useful when converted to allicin.

Other Cardiovascular Benefits of Garlic and Allicin

Besides lowering cholesterol levels, studies have shown that garlic can improve cardiovascular health by other means.

In a 1991 study published in the Journal of Postgraduate Medicine, the effects of garlic on serum cholesterol and blood clotting were investigated. The researchers gave 10 g of raw garlic to some young adults every day for 2 months while the control group only received placebo.

After 2 months, the researchers found that there were no changes in serum cholesterol, fibrinolytic activity and clotting time in the control group. On the other hand, the participants who ate raw garlic had lower serum cholesterol levels. In addition, clotting time and fibrinolytic activity were increased in this group.

This study shows that besides its cholesterol-lowering activity, garlic can also act as an anticoagulant and reduce the risks of thromboembolic events like heart attack and stroke.

A 2000 study published in the journal, Prostaglandins, Leukotrienes and Essential Fatty Acids, also found out that besides the cholesterol-lowering effect of garlic allicin, the compound can also reduce the risk of atherosclerosis by relieving high blood pressure.

Another benefit for cardiovascular health was confirmed by a 2004 study published in The Journal of Nutritional Biochemistry.

In that study, the researchers studied the effects of garlic supplementation on blood lipid profile and lipid peroxidation in a group of patients with diagnosed hypercholesterolemia.

The results of this study showed that garlic extract

  • Significantly reduced serum total cholesterol, LDL cholesterol, VLDL cholesterol and triglyceride levels
  • Increased HDL cholesterol level
  • Reduced blood pressure in patients with hypertension
  • Increased blood antioxidant potential while reducing oxidative stress

This study shows that garlic can improve lipid profile; prevent lipid oxidation and the damage that can cause to the arteries; and reduce blood pressure. All of these results are beneficial to cardiovascular health.

Sources


http://www.webmd.com/cholesterol-management/news/20070226/garlic-may-not-lower-cholesterol

http://news.bbc.co.uk/2/hi/health/6396405.stm

http://www.medicalnewstoday.com/articles/63976.php

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