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Garlic Reduces Blood Pressure

 

Garlic Reduces Blood Pressure

A meta-analysis of 20 studies (970 participants) suggested that garlic supplements potentially can lower blood pressure in patients with hypertension, regulate slightly elevated cholesterol concentrations, and stimulate the immune system (Reid 2016). Reid found a mean decrease in systolic blood pressure (SBP) of 5.1 ± 2.2 mm Hg (P < 0.001) and a mean decrease in diastolic blood pressure (DBP) of 2.5 ± 1.6 mm Hg (P < 0.002) compared with placebo. Garlic worked even better on people with existing high blood pressure. People with hypertension had a significant reduction in SBP of 8.7 ± 2.2 mm Hg (P < 0.001; n = 10) and in DBP of 6.1 ± 1.3 mm Hg (P < 0.001; n = 6). 

An earlier meta-analysis of 11 studies found that garlic preparations were superior to placebos in reducing both SBP and DBP in people with hypertension (Reid et al. 2008). Garlic supplements had no significant effect on people with normal blood pressure. Reid et al. (2008) reported a mean decrease of 4.6 ± 2.8 mm Hg for SBP in the garlic group compared to placebo (n = 10; p = 0.001), while the mean decrease in the hypertensive subgroup was 8.4 ± 2.8 mm Hg for SBP (n = 4; p < 0.001), and 7.3 ± 1.5 mm Hg for DBP (n = 3; p < 0.001).

Likewise, Wang et al. (2015) reported that their meta-analysis suggested that garlic supplements were superior to the placebo in lowering blood pressure in people with hypertension.

I know some people like to see individual studies so I've highlighted a few recent health studies below. In the past there has been some contention about garlic lowering blood pressure. However, recently there has been a avalanche of new studies showing that garlic reduces blood pressure in people who already have high blood pressure. In addition to the human trials, rat studies are starting to tease out the biochemical mechanisms responsible for the drop in blood pressure. Grey Duck Garlic, Red Rezan garlic bulbs on rock

Picture: Tasty and healthy Red Rezan garlic bulbs rest on rock.

Aged Garlic Reduces Systolic Blood Pressure in People with Hypertension

Reid et al. (2016) reported that Kyolic aged garlic extract significantly reduced peripheral and central blood pressure in adults with uncontrolled hypertension. There was a positive trend for aged garlic extract to improve arterial stiffness, inflammation, and other cardiovascular markers in patients as well. The garlic extract had a high safety profile and was easily tolerated by people.

In this double-blind randomized placebo controlled trial, people with hypertension (n=79) were given either a placebo or 1, 2, or 4 aged garlic capsules (240/480/960 mg containing 0.6/1.2/2.4 mg of S-allylcysteine) for 12 weeks. Mean SBP was significantly reduced by 11.8±5.4mmHg in the 2 capsule garlic group at 12 weeks compared with placebo (P=0.006), and reached borderline significant reduction in the 4 capsule garlic group at 8 weeks (-7.4±4.1 mmHg, P=0.07). Changes in SBP in the 1 capsule garlic group and diastolic blood pressure were not significantly different to placebo (Ried et al. 2013).

Garlic Reduces Blood Pressure in a Dose Dependant Fashion

People with hypertension (n=210) were given either a placebo, the antihypertension beta-blocker Atenolol or garlic tablets at a dose of 300/mg. 600/mg, 900/mg, 1200/mg and 1500/mg for 24 weeks. People treated with garlic tablets had a significant and dose dependant decrease in SBP and DBP when compared to those receiving either Atenolol or a placebo (Ashraf et al. 2013).

Garlic Lowers Blood Pressure in Treated But Uncontrolled Hypertension

Patients (n=50) with treated (with medication) but still high blood pressure took either a placebo or aged garlic extract (960 mg containing 2.4 mg S-allylcysteine) for 12 weeks. People treated with garlic had a 10.2 ± 4.3 mmHg (p=0.03) drop in SBP compared to controls. In addition, the garlic treatment was well tolerated by 92% of the patients (Ried et al. 2010).

Traditional Japanese Garlic Preparation Lowers Blood Pressure

Nakasone et al. (2013) reported the effect of treatment with either 300 mg garlic homogenate-based diet or a placebo on people with prehypertension (n=34) or mild hypertension (n=47) for 12 weeks. The garlic treatment induced significant reductions of SBP (6.6-7.5 mmHg) and DBP (4.6-5.2 mmHg) when compared to the placebo. 

Garlic Reduces Blood pressure in People with Elevated Systolic Blood Pressure

This meta-analysis of ten trials found that garlic treatment reduced SBP by 16.3 mm Hg (95% CI 6.2 to 26.5) and DBP by 9.3 mm Hg (95% CI 5.3 to 13.3) compared with placebo in people with elevated SBP. Interestingly, garlic treatment did not reduce SBP or DBP in patients without elevated SBP (Reinhart et al. 2008). 

Adding Garlic to a Blood Pressure Lowering Medication, Captophil, has a Synergistic Effects in Hypertensive Rats

Hypertension can be induced by giving rats a 10% fructose solution. Asdaq and Inamdar (2010) gave hypertensive rats fresh garlic homogenate (FGH), the bioactive sulphur compound S-allyl cysteine sulphoxide (SACS) derived from fresh garlic and/or the antihypertensive medication Captophil (CAP).

FGH (250 mg/kg) + CAP (30 mg/kg) was more effective at reducing systolic blood pressure, cholesterol, triglycerides and glucose than the FGH, SACS, CAP or SACS+CAPS. Treatment with FGH + CAP had a higher synergistic action than SACS (0.222 mg/kg) + CAP. This means that more than one compound in garlic is responsible for garlic's ability to lower blood pressure.

The combination of SACS + CAP showed synergistic interaction with respect to fall in blood pressure and ACE inhibition.

Possible Garlic Antihypertension Mechanisms:

Allicin in garlic is converted by red blood cells into hydrogen sulfur. Hydrogen sulfur helps regulates blood vessel dilation and size. Extra hydrogen sulfate causes blood vessels to relax and allow greater blood flow through the vessels. This can lower blood pressure.

A recent review determined that numerous factors may influence garlic's antihypertensive effects including garlic bioactives like S-allyl cysteine and allicin. Garlic may influence oxidative stress, nitric oxide bioavailability, hydrogen sulfide production, angiotensin converting enzyme activity, expression of nuclear factor-κB and the proliferation of vascular smooth muscle cells. All these factors are implicated in the pathogenesis of hypertension (Shouk et al. 2014).

Take home message: If you have elevated blood pressure (especially if your systolic blood pressure is high) eating a clove of garlic everyday may help. After reading numerous garlic studies I have come to the conclusion that garlic health benefits come from multiple components. Consuming the whole clove or a whole prepared supplement will have a better effect than taking isolated compounds derived from garlic.

You may also note that feeding rats fructose makes rats develop diabetes and high blood pressure. Humans aren't rats, which is why I try to include mostly human studies (with some animal work to back it up), but the fructose connection is something to think about. There are a lot of studies linking consuming excess sugars (including fructose) and carbohydrates to inflammation and metabolic syndrome.

by Susan Fluegel, PHD

References:

  • Asdaq SM, Inamdar MN. Potential of garlic and its active constituent, S-allyl cysteine, as antihypertensive and cardioprotective in presence of captopril. Phytomedicine. 2010;17:1016-26. Pubmed. doi: 10.1016/j.phymed.2010.07.012
  • Ashraf R, Khan RA, Ashraf I, Qureshi AA. Effects of Allium sativum (garlic) on systolic and diastolic blood pressure in patients with essential hypertension. Pak J Pharm Sci. 2013;26:859-63. Pubmed.
  • Nakasone Y, Nakamura Y, Yamamoto T, Yamaguchi H. Effect of a traditional Japanese garlic preparation on blood pressure in prehypertensive and mildly hypertensive adults. Exp Ther Med. 2013;5:399-405. Pubmed. Full text.
  • Reid K. Garlic lowers blood pressure in hypertensive individuals, regulates serum cholesterol, and stimulates immunity: an updated meta-analysis and review. J Nutr. 2016;146:389S-396S. Pubmed. doi: 10.3945/jn.114.20219
  • 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;67:144-50. Pubmed. doi: 10.1016/j.maturitas.2010.06.001
  • Ried K, Frank OR, Stocks NP. Aged garlic extract reduces blood pressure in hypertensives: a dose-response trial. Eur J Clin Nutr. 2013;67:64-70. Pubmed. doi: 10.1038/ejcn.2012.178 (full text)
  • Reid K, Frank OR, Stocks, NP, Fakler P, Sullivan T. Effect of Garlic on Blood Pressure: a systemic review and meta-analysis. BMC Cardiovascular Disord. 2008;16:8:13. Full text.
  • Ried K, Travica N, Sali A. The effect of aged garlic extract on blood pressure and other cardiovascular risk factors in uncontrolled hypertensives: the AGE at Heart trial. 2016;9:9-21. Full text.doi: 10.2147/IBPC.S93335
  • Reinhart KM, Coleman CI, Teevan C, Vachhani P, White CM. Effects of garlic on blood pressure in patients with and without systolic hypertension: a meta-analysis. Ann Pharmacother. 2008;42:1766-71. Pubmed. doi: 10.1345/aph.1L319
  • Shouk R, Abdou A, Shetty K, Sarkar D, Eid AH. Mechanisms underlying the antihypertensive effects of garlic bioactives. Nutr Res. 2014;34:106-15. Pubmed. doi: 10.1016/j.nutres.2013.12.005
  • Wang HP1, Yang J, Qin LQ, Yang XJ. Effect of garlic on blood pressure: a meta-analysis. J Clin Hypertens. 2015;17:223-31. doi: 10.1111/jch.12473

 

 

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