Garlic

Garlic

Other names: Allium sativum.

Description:

Garlic is the edible bulb from a plant in the lily family.

Mechanism of action:

Diallyl disulfide is a component of garlic oil that has been found to inhibit 3-hydroxy-3-methylglutaryl CoA (HMG CoA) reductase in a concentration-dependent manner. HMG CoA reductase is a key enzyme in the formation of cholesterol synthesis; thus, its inhibition reduces cholesterol formation, similar to the mechanism of action of statin medication.

It is hypothesized that garlic improves blood pressure through inhibition of angiotensin-converting enzyme (ACE), down-regulation of angiotensin II receptor, and through stimulation of nitric oxide formation.

Garlic is also thought to have antimicrobial and anti-viral properties.

Common indications/uses:

Hyperlipidemia

Hypertension

Common cold prevention

Dosing:

2–5 g of fresh raw garlic

300–2400 mg/day

Evidence:

The most comprehensive meta-analysis conducted to date included 39 primary trials evaluating the effect on garlic preparation on total cholesterol, LDL-cholesterol, HDL-cholesterol, and triglycerides. The study revealed that garlic was effective in reducing total serum cholesterol and LDL-cholesterol in individuals with elevated total cholesterol levels if used for longer than 2 months. The observed mean reduction of total serum cholesterol was 8% and was associated with a 38% reduction in risk of coronary events at 50 years of age. HDL-cholesterol levels improved only slightly, and triglycerides were not influenced significantly. Despite these findings, there continues to be ongoing controversy whether garlic supplementation can truly and significantly impact hyperlipidemia.  

Most clinical trials support the assumption that garlic may moderately decrease arterial blood pressure in hypertensive subjects. A meta-analysis of seven randomized placebo-controlled trials reported a significant lowering effect of garlic on both systolic and diastolic blood pressure, by 6.7 and 4.8 mmHg, respectively.  

In one 12-week randomized controlled trial of 146 participants evaluating cold prevention with garlic supplementation versus placebo and standard treatment demonstrated 24 occurrences of the common cold in the intervention group as compared to 65 in the placebo group. The trial also revealed a few days of illness (111 versus 366). Seeing as there is only one randomized controlled trial supporting Garlic's effect on cold prevention, more evidence is needed.

Safety concerns:

Garlic is generally considered a safe supplement. The known adverse effects are considered mild, nevertheless attention should be paid to its few herb-drug interactions.

Adverse reactions:

Side effects are more noticeable with raw garlic. The most commonly documented side effects are breath and body odor. Other side effects include heartburn, upset stomach, and applied directly on skin, burns are possible. As like many other substances, there is also a risk of allergic reaction.

Drug interactions:

As garlic supplementation may increase the risk of bleeding, bleeding risk may be further exacerbated with concurrent use of anticoagulants such as Warfarin.

Garlic may reduce the efficacy of anti-AIDS drugs such as Saquinavir.