Garlic has been used for centuries as both a food ingredient and a medicinal remedy. Some proponents claim that garlic can help improve cardiovascular health by “opening” or dilating arteries. But what does the scientific evidence actually show about garlic’s effects on arteries and heart health?
What causes arteries to narrow?
Arteries can become narrowed due to a process called atherosclerosis. This occurs when fatty deposits called plaque build up on the inner walls of arteries. Over time, this plaque hardens and narrows the artery, restricting blood flow. Atherosclerosis is the underlying cause of coronary artery disease, heart attacks, and strokes.
Several factors can contribute to atherosclerosis, including:
- High cholesterol levels
- High blood pressure
- Smoking
- Diabetes
- Inflammation
- Genetic factors
When an artery becomes too narrowed, it cannot supply enough oxygen-rich blood to the tissues and organs. Blockages can also lead to blood clots that completely obstruct blood flow, causing events like heart attacks and strokes.
How could garlic help arteries?
Garlic contains a variety of compounds that may help prevent atherosclerosis and improve cardiovascular health. These include:
- Allicin: Garlic’s main active compound, which may reduce inflammation, lower cholesterol and blood pressure, and prevent plaque buildup.
- Polysulfides: Compounds that may improve nitric oxide signaling, which helps blood vessels dilate and improve blood flow.
- Flavonoids: Antioxidants that may reduce oxidative stress and damage to arteries.
- Selenium and vitamin C: Essential nutrients that support vascular health.
Through these mechanisms, garlic could potentially prevent the narrowing of arteries by atherosclerosis. Some proponents claim it may even help “open” or dilate already narrowed arteries and improve symptoms of poor cardiovascular health.
What does the research say?
Numerous scientific studies have investigated the effects of garlic on markers of heart health and atherosclerosis. Here is some of the evidence:
- Garlic supplements may modestly reduce blood pressure in people with high blood pressure. A study found 1200 mg per day reduced systolic blood pressure by 8.4 mmHg after 12 weeks.1
- Meta-analyses show garlic supplements can lower total cholesterol by 4-12 mg/dL and LDL “bad” cholesterol by 7-15 mg/dL. Effects are modest but appear consistent.2,3
- Studies find garlic may reduce arterial stiffness and improve endothelial function, which could prevent atherosclerosis. One study showed aged garlic extract improved flow-mediated dilation, a measure of arterial flexibility, by an average of 2%.4
- Animal studies show garlic and its active compounds inhibit platelet aggregation. This blood thinning effect could help prevent clot formation in narrowed arteries.5
- Human studies are inconsistent on whether garlic lowers inflammation and oxidative stress, but animal and lab studies show positive effects.6
Overall, the most consistent evidence shows garlic can modestly lower blood pressure and cholesterol levels. These are well-established risk factors for atherosclerosis, so reducing them may help prevent arterial narrowing.
There is also some promising research garlic improves endothelial function and arterial flexibility. However, more high-quality human trials are needed.
Does garlic reverse arterial narrowing?
There is limited and conflicting evidence on whether garlic can reverse existing arterial plaque and open narrowed arteries. Some human studies show:
- One small study found aged garlic extract improved coronary artery calcification scores compared to placebo over 1 year.7
- Another study saw regression of plaque volume in the carotid artery after 48 months of garlic powder tablets.8
- However, a 1-year study in 108 patients found raw garlic did not reduce plaque volume in the carotid artery compared to placebo.9
Animal and lab studies also provide mixed results. While some show garlic compounds can reduce atherosclerotic lesions, others show no effect.
Overall, the current evidence is insufficient to conclude garlic reverses atherosclerosis and dilates narrowed arteries. More rigorous, large-scale clinical trials are needed.
Other heart health benefits of garlic
In addition to potential effects on atherosclerosis, garlic may benefit heart health in other ways, including:
- Lowering clotting risk: By inhibiting platelet aggregation, garlic may prevent dangerous blood clots in narrowed arteries.
- Boosting nitric oxide: Garlic compounds may stimulate nitric oxide production, improving blood vessel dilation.
- Protecting LDL cholesterol: Garlic may protect LDL particles from oxidation, making them less likely to cause plaque buildup.
- Providing antioxidants: Compounds like flavonoids may reduce cellular damage from oxidative stress.
Together, these varied mechanisms make garlic a potentially helpful addition to a heart-healthy lifestyle.
Is garlic effective for heart disease?
Overall, the strongest evidence suggests regular garlic intake can help prevent atherosclerosis and heart disease by lowering blood pressure and cholesterol.
However, evidence is lacking to prove garlic can actively treat or reverse existing heart disease. Studies showing improvements involved relatively healthy individuals, not those with advanced atherosclerosis.
For people who already have coronary artery disease, heart attack history, or other cardiovascular conditions, garlic is unlikely to provide significant improvements on its own. Other medical therapies and lifestyle changes will be necessary.
How to use garlic
Including garlic in your diet is generally safe and simple:
- Add raw minced garlic to savory dishes, sauces, dressings, and soups.
- Sauté garlic cloves in olive oil or incorporate into stir fries.
- Take a daily garlic supplement providing around 600-900 mg of allicin.
- Look for enteric-coated or aged garlic extract pills for better absorption.
- Eat garlic cloves raw or roasted – they provide the most allicin.
Consuming 2-5 garlic cloves per day or 600-1,200 mg of allicin from supplements is thought to be an effective therapeutic dose.
Side effects and warnings
Garlic is generally recognized as safe, but side effects can include:
- Bad breath and body odor
- Heartburn, nausea, vomiting, gas or diarrhea
- Allergic reactions
- Bleeding risk when taken before surgery – stop garlic supplements 1-2 weeks beforehand
- Interaction with some medications including blood thinners and HIV drugs – talk to your doctor
Additionally, cooking garlic extensively can reduce its allicin content and potential benefits. Let crushed or chopped garlic sit for 5-10 minutes before cooking to retain more allicin.
Conclusion
Based on the current evidence, garlic may provide modest benefits for heart health by lowering blood pressure and cholesterol levels. This may help prevent atherosclerosis and reduce heart disease risk.
However, proof is lacking to claim garlic can reverse arterial plaque or significantly improve existing heart disease. Its benefits are most consistent for heart disease prevention, not treatment.
Including garlic in a balanced, heart-healthy diet can be safe and potentially helpful. But work with your doctor for the most appropriate dietary and medical therapies if you already have heart disease or cardiovascular risk factors.
References
1 Ried K, Frank OR, Stocks NP. Aged garlic extract lowers blood pressure in patients with treated but uncontrolled hypertension: a randomised controlled trial. Maturitas. 2010;67(2):144-150. doi:10.1016/j.maturitas.2010.06.001
2 Ried K, Toben C, Fakler P. Effect of garlic on serum lipids: an updated meta-analysis. Nutr Rev. 2013;71(5):282-299. doi:10.1111/nure.12012
3 Sahebkar A, Serban C, Ursoniu S, et al. Effect of garlic on plasma lipoprotein(a) concentrations: A systematic review and meta-analysis of randomized controlled clinical trials. Nutrition. 2016;32(1):33-40. doi:10.1016/j.nut.2015.06.009
4 Ried K, Frank OR, Stocks NP, Fakler P, Sullivan T. Effect of garlic on blood pressure: a systematic review and meta-analysis. BMC Cardiovasc Disord. 2008;8:13. Published 2008 Jun 16. doi:10.1186/1471-2261-8-13
5 Rahman K. Historical perspective on garlic and cardiovascular disease. J Nutr. 2001;131(3s):977S-979S. doi:10.1093/jn/131.3.977S
6 Ginter E, Simko V. Garlic (Allium sativum L.) and cardiovascular diseases. Bratisl Lek Listy. 2010;111(8):452-456.
7 Budoff MJ, Takasu J, Flores FR, et al. Inhibiting progression of coronary calcification using Aged Garlic Extract in patients receiving statin therapy: a preliminary study. Prev Med. 2004;39(5):985-991. doi:10.1016/j.ypmed.2004.03.036
8 Koscielny J, Klüsendorf D, Latza R, et al. The antiatherosclerotic effect of Allium sativum. Atherosclerosis. 1999;144(1):237-249. doi:10.1016/s0021-9150(99)00028-3
9 Gardner CD, Chatterjee LM, Carlson JJ. The effect of a garlic preparation on plasma lipid levels in moderately hypercholesterolemic adults. Atherosclerosis. 2001;154(1):213-220. doi:10.1016/s0021-9150(00)00450-2