With approximately 70 million American adults having high blood pressure, hypertension is one of the United States' more ubiquitous diseases. Medical nutrition therapy — centered on the DASH diet, weight management and increased physical activity — has proven to be effective in hypertension management, while physicians often will prescribe medications, as well.
Recent interest in supplements, their effectiveness and potential drug interactions may prompt inquiries from patients diagnosed with hypertension. Although foods and compounds hailing from the traditions of folk medicine are the subject of safety and efficacy studies in the treatment of high blood pressure, one trendy supplement is everyone's favorite little aromatic: garlic.
With a long, varied history of medicinal use, garlic supplementation for decreasing diastolic and systolic blood pressure is rated as possibly effective on the Natural Medicines Comprehensive Database. Similar to some pharmaceuticals, garlic appears to help in vasodilation, or widening of blood vessels due to relaxation of the muscular walls of the vessels. It also may inhibit angiotensin II, a naturally occurring substance in the body that narrows blood vessels and increases blood pressure.
To be clear, the evidence is not strong enough to suggest that garlic preparations may be used as an alternative to prescription medication, and garlic supplementation should not replace dietary, lifestyle or medical interventions for hypertension. A 2007 literature review found the evidence supporting garlic's positive effect on blood pressure to be "limited." However, more recent research suggests garlic may have a modest effect on lowering systolic and diastolic blood pressure in individuals with hypertension.
So what is it about garlic? The answer may be the antioxidant allicin, a sulfur compound that not only is responsible for the garlicky aroma, but also has been identified as the potential beneficial constituent to health. Allicin is formed when fresh garlic is crushed and begins degrading almost immediately. For this reason, along with factoring the amount of fresh garlic consumption required to reap the potential benefits related to hypertension, garlic supplements have become popular. Available through natural grocers, online and in vitamin stores, garlic supplements range in format (typically tablets or capsules) and formulations, including dried garlic powder, powder extracts and macerated oils — each with different claims of benefits and bioavailability.
Garlic has been used safely in human clinical studies lasting up to seven years without reports of significant adverse effects, and doses higher than would be administered to humans have been tested without toxicity in animals. Although many studies did not report adverse events, when side effects were noted, they included malodorous breath or body odor, gastrointestinal symptoms such as nausea, vomiting, flatulence or diarrhea and allergic reactions for those with a garlic allergy.
There also are some drug-nutrient interactions of moderate and major effects to discuss with patients interested in garlic supplementation, including blood thinning and blood pressure medications, contraceptive drugs, tuberculosis medications and several HIV/AIDS medications.
Due to the wide range of product types — and because dietary supplements do not require FDA approval — consumers should look for independent quality assessment seals and third-party verification about a product's ingredients and quantities.