Flashback Friday: Inhibiting Platelet Activation with Garlic and Onions

As we age, our arteries stiffen. These are measurements of the stiffness of our aorta, the main artery coming off the heart, as we get older and older. As our aorta stiffens, it leads to a range of pathological changes, such as exposing our brain and kidneys to greater pressure fluctuations, which may increase the risk of stroke and impairment of kidney function.

Those who consume garlic, though, just less than a quarter teaspoon of garlic powder a day, appear to have less stiffness in their aortas. We think this is because garlic seems to improve the function of the inner lining of our arteries, which helps our arteries relax. But the protective mechanisms of garlic against cardiovascular diseases are multiple, and include a combination of anti-clotting, clot-busting, antioxidant, and blood pressure and cholesterol lowering effects.  The latest review suggests a long-term garlic intake may drop bad cholesterol levels about 10%, but the blood thinning effects are such that the American Society of Anesthesiology recommends garlic intake be stopped a week before elective surgery.

Or, presumably, you could just cook it to death. Unlike the anti-clotting components concentrated in the yellow fluid around tomato seeds, which are heat stable, the antiplatelet activity in garlic and onions is lost with cooking.  Here’s the platelet inhibition of raw garlic compared to boiled garlic, which was down around raw onion. So, garlic appears about 13 times more potent than onion, and raw appears to be better than cooked, suggesting that garlic and onion could be more potent inhibitors of blood clotting if consumed in raw than in cooked or boiled form. So, right before surgery it might be good to cook garlic, but what about the rest of the time when we’re trying to suppress platelet overactivity to decrease the risk of heart attacks and stroke? As garlic and onion are normally consumed in cooked food, their efficacy as preventive herbs in cardiovascular disease may be doubtful. But we can put some raw onion on salads, raw garlic in salsa, dressings, dips, or pesto.

Or we can crush or chop it, wait ten minutes and then cook it. Here’s the platelet inhibiting power of raw garlic, and if you cook it just a few minutes, it does fine, but after cooking like five minutes, the effect is abolished. But if you pre-crush and wait, some of the antiplatelet activity is retained a bit longer. That’s because the enzyme that makes the antiplatelet compounds is activated by crushing, but destroyed by heat faster than the compounds it creates. So, by crushing first and letting the enzyme work its magic before cooking, one can delay the loss of function.

Even better though, just like we can add broccoli enzymes in the form of raw radish or mustard powder to boost the benefits of broccoli, the addition of a little raw garlic juice to cooked garlic can restore the full complement of antiplatelet activity that was completely lost without the raw garlic addition.

When onions are cooked, the antiplatelet activity is similarly abolished within ten minutes. But then something strange happens. After 20 or 30 minutes of cooking, the effect on platelets is reversed and appears to make matters worse. Significant pro-platelet activation effects, suggesting that extensively cooked onions may stimulate rather than inhibit platelets. This was in a test tube, though. Thankfully, when tested in people, even when onions are dropped in boiling water, fried for ten minutes, and then left to simmer for 30, platelet activation drops within an hour and three hours after onion soup ingestion.

To see any graphs, charts, graphics, images, and quotes to which Dr. Greger may be referring, watch the above video. This is just an approximation of the audio contributed by Katie Schloer.

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• A K Dutta-Roy, L Crosbie, M J Gordon. Effects of tomato extract on human platelet aggregation in vitro. Platelets. 2001 Jun;12(4):218-27.
• M Ali, T Bordia, T Mustafa. Effect of raw versus boiled aqueous extract of garlic and onion on platelet aggregation. Prostaglandins Leukot Essent Fatty Acids. 1999 Jan;60(1):43-7.
• G P Hubbard, S Wolffram, R de Vos, A Bovy, J M Gibbins, J A Lovegrove. Ingestion of onion soup high in quercetin inhibits platelet aggregation and essential components of the collagen-stimulated platelet activation pathway in man: a pilot study. Br J Nutr. 2006 Sep;96(3):482-8.
• K K Lau, Y H Chan, Y K Wong, K C Teo, K H Yiu, S Liu, L S Li, X O Shu, S L Ho, K H Chan, C W Siu, H F Tse. Garlic intake is an independent predictor of endothelial function in patients with ischemic stroke. J Nutr Health Aging. 2013 Jul;17(7):600-4.
• A Lawn, P Sains. Comment on: Not just a vampire repellent: the adverse effects of garlic supplements in surgery.Ann R Coll Surg Engl. 2012 Sep;94(6):451.
• K Ried, C Toben, P Fakler. Effect of garlic on serum lipids: an updated meta-analysis. Nutr Rev. 2013 May;71(5):282-99.
• U Quinn, L A Tomlinson, J R Cockcroft. Arterial stiffness. JRSM Cardiovasc Dis. 2012 Sep 30;1(6).
• K Breithaupt-Grögler, M Ling, H Boudoulas, G G Belz. Protective effect of chronic garlic intake on elastic properties of aorta in the elderly. Circulation. 1997 Oct 21;96(8):2649-55.
• A Wong, S A Townley. Herbal medicines and anaesthesia. Continuing Education in Anaesthesia, Critical Care & Pain | Volume 11 Number 1 2011.
• P F Cavagnaro, C R Galmarini CR. Effect of processing and cooking conditions on onion (Allium cepa L.) induced antiplatelet activity and thiosulfinate content. J Agric Food Chem. 2012 Sep 5;60(35):8731-7.
• P F Cavagnaro, A Camargo, C R Galmarini, P W Simon. Effect of cooking on garlic (Allium sativum L.) antiplatelet activity and thiosulfinates content. J Agric Food Chem. 2007 Feb 21;55(4):1280-8.

Images thanks to HolgersFotografie via Pixabay.