Cardiovascular claims for the “stinking rose” find support with the identification of relevant artery and cell effects
by Craig Weatherby
Garlic's reputation as a heart-healthy food explains why garlic pills outsell every other herbal supplement in the US, with some $100 million worth being bought every year.
Several clinical studies have shown minor reductions in total blood cholesterol and LDL (“bad”) cholesterol, minor reductions in the progression of atherosclerosis (buildup of arterial plaque), and minor reductions in blood pressure and stickiness (platelet aggregation).
But, as the respected Natural Standard Research Collaboration says in their summary of the evidence, “Long-term effects on lipids or cardiovascular morbidity and mortality remain unknown” (NSRC 2007).
So the results of a new study raise hope among its many fans that garlic may yet be proven to help hearts.
Garlic found to relax arteries
Earlier this year, researchers from the University of Alabama at Birmingham published a study confirming that hydrogen sulfide causes arteries to relax, just as the better known bodily chemical nitric oxide does (Koenitzer JR et al 2007).
(Viagra® works by inducing release of nitric oxide, which causes blood vessels to dilate, thereby increasing blood flow to the male member.)
The body produces hydrogen sulfide naturally, but production of the compound drops as we grow older.
These same researchers knew that cardiovascular disease progresses more slowly in heavy garlic eaters, and that garlic is rich in sulfur compounds, so they decided to look for a possible connection between those chemicals and our own hydrogen sulfide.
Prior research has narrowed the active constituents in garlic down to a “parent” sulfur compound called allicin.
Once exposed to air, water or blood, allicin quickly degrades to form four smaller compounds, called diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DATS), and ajoene.
The Alabama team extracted juice from garlic and added minute amounts to human red blood cells, which began emitting hydrogen sulfide in response.
The researchers then cut sections from the heart arteries (aortas) of rats, and exposed these “aorta rings” to the same garlic extract.
As with the human red blood cells, the rat aorta cells emitted hydrogen sulfide.
More importantly, the garlic extract reduced tension within the artery sections, and did it in a dose-dependent manner. That is, the more sulfides the artery sections were exposed to, the more relaxed and dilated they became.
This effect could account for the observed ability of garlic to lower blood pressure modestly in people with hypertension.
As the authors wrote, “We propose that hydrogen sulfide production from these garlic-derived organic polysulfides provides the basis for the long-term beneficial effects obtained from the habitual consumption of garlic” (Benavides GA et al 2007).
Garlic sulfide also prevents inflammation and cell damage
Its apparent artery-relaxing/dilating effect doesn’t explain fully why the hydrogen sulfide released by blood cells in response to garlic sulfides would slow the progression of atherosclerosis.
However, the results of another study published this year indicate that hydrogen sulfide prevents the inflammation and cell (mitochondrial) damage associated with heart attacks and ischemia (Elrod JW et al 2007).
Ischemia is the medical term for the state of reduced blood flow that can result either from clogged arteries, as in atherosclerosis, or from weakened heart muscles, as in congestive heart failure. Atherosclerosis often precedes congestive heart failure.
The Alabama team also proposed that the efficacy of various kinds of garlic supplements (fresh, aged, etc.) could be judged by the amounts of hydrogen sulfide they produce under simulated bodily conditions.
We should note that excessive consumption of supplemental garlic can increase the effects of blood thinning drugs and produce internal bleeding, so don’t take them if you are on blood thinners like warfarin or coumadin.
- Benavides GA, Squadrito GL, Mills RW, Patel HD, Isbell TS, Patel RP, Darley-Usmar VM, Doeller JE, Kraus DW. Hydrogen sulfide mediates the vasoactivity of garlic. Proc Natl Acad Sci U S A. 2007 Oct 19; [Epub ahead of print]
- Koenitzer JR, Isbell TS, Patel HD, Benavides GA, Dickinson DA, Patel RP, Darley-Usmar VM, Lancaster JR Jr, Doeller JE, Kraus DW. Hydrogen sulfide mediates vasoactivity in an O2-dependent manner. Am J Physiol Heart Circ Physiol. 2007 Apr;292(4):H1953-60. Epub 2007 Jan 19.
- Elrod JW, Calvert JW, Morrison J, Doeller JE, Kraus DW, Tao L, Jiao X, Scalia R, Kiss L, Szabo C, Kimura H, Chow CW, Lefer DJ. Hydrogen sulfide attenuates myocardial ischemia-reperfusion injury by preservation of mitochondrial function. Proc Natl Acad Sci U S A. 2007 Sep 25;104(39):15560-5. Epub 2007 Sep 18.