Garlic's heart benefits pinpointed
may also be the source of its heart benefits, according to new
research from the US.
Metabolism of garlic's active ingredient allicin produces hydrogen sulphide, which signals blood vessels to relax, increase blood flow and boost heart health, wrote the researchers in the prestigious Proceedings of the National Academy of Sciences. The research could lead to a method to standardise dietary garlic supplements, said lead researcher Gloria Benavides from the University of Alabama at Birmingham, by simply measuring the production of hydrogen sulphide in red blood cells. Like all plants, garlic varies greatly from crop to crop in its make-up and the amount of allicin in regular garlic supplements varies greatly, with much destroyed through the distillation process or by stomach acid and heat. The research was welcomed by a UK-based expert as "interesting study", but Judy O'Sullivan from the British Heart Foundation stressed that excessive consumption of garlic in supplemental form may adversely interact with blood thinning drugs and produce dangerous side effects. Benavides and co-workers extracted juice from supermarket garlic and added minute amounts to human red blood cells. Allicin is unstable in aqueous solution and quickly decomposes to form diallyl sulfide (DAS), diallyl disulfide (DADS), diallyl trisulfide (DATS), and ajoene. Once exposed to these compounds, the red blood cells immediately began emitting hydrogen sulphide. Additional experiments showed that the key chemical reactions occurred at the surface of the red blood cells. The researchers then used intact aorta rings from rats and, under physiologically relevant oxygen levels, exposed the rings, a model for blood vessels, to the garlic-derived organic polysulfides. Again, liberated hydrogen sulphide was observed. It was also observed that the garlic extracts reduced the tension within the vessels in a dose-dependent manner. A 200 micromole garlic solution relaxed the vessels by 40 per cent, while a 500 micromoles per millilitre solution of garlic relaxed the vessels by 75 per cent. "Few plants other than garlic contain allyl-substituted sulfur compounds, and garlic is the only one of these with a dietary use," wrote the authors. "We propose that hydrogen sulphide production from these garlic-derived organic polysulphides provides the basis for the long-term beneficial effects obtained from the habitual consumption of garlic," they added. Commenting independently on the research, O'Sullivan said: "This interesting study suggests that garlic may provide some heart health benefits. "However, there remains insufficient evidence to support the notion of eating garlic as medicine in order to reduce the risk of developing coronary heart disease." Indeed, researchers meeting under the auspices of the US National Heart, Lung and Blood Institute in 2002 found that there was little scientific data to support many of the claims about garlic. Consumer awareness of the health benefits of garlic, mostly in terms of cardiovascular and immune system health, has benefited the supplements industry, particularly since consumers seek the benefits of garlic without the odours that accompany the fresh bulb. Garlic supplements are worth more than $100m (€79.5m) in the US and are also one of the biggest sellers in the UK market. According to a 1998 survey by Hartman and New Hope, garlic supplements are used twice as much as other herbal supplements. Source: Proceedings of the National Academy of Sciences (PNAS) Published on-line ahead of print, ARTICLE #07-05710, doi: 10.1073/pnas.0705710104 "Hydrogen sulfide mediates the vasoactivity of garlic" Authors: Gloria A. Benavides, G.L. Squadrito, R.W. Mills, H.D. Patel, T.S. Isbell, R.P. Patel, V.M. Darley-Usmar, J.E. Doeller, and D.W. Kraus