Much of the research on garlic has focused on the organosulfur compounds, or OSCs, found in the whole clove, which are responsible for its flavor and distinct smell. While allicin is probably the best recognized of the OSCs, there are actually many different types of OSCs found in garlic. Some of these compounds, like allicin are dependent on enzymes that are activated when garlic is crushed, chopped, or chewed. Others, like those found in aged garlic supplements, are formed during the aging process or are formed as breakdown products of other OSCs.² These OSCs are believed to be responsible for the majority of the health benefits of garlic though polyphenolic compounds and prebiotic fibers in garlic may also contribute to its health benefits. 

Cardiovascular Benefits

Probably the best researched and most celebrated benefit of garlic is its ability to benefit the cardiovascular system. Indeed, garlic has long been used for conditions that affect the cardiovascular system. Research studies show that garlic supplements are quite useful for the treatment of uncontrolled hypertension, lowering blood pressure by about 10 mmHg systolic and 8 mmHg diastolic, similar to standard blood pressure medications.³ Mechanisms by which garlic reduces blood pressure include inhibiting the aggregation of platelets, thus keeping the blood flowing smoothly,⁴ relaxing the blood vessels, and even blocking production of hormones that cause blood pressure to increase.⁵ Garlic may also benefit the cardiovascular system by reducing LDL cholesterol levels and modulating inflammation.⁶

Antimicrobial and antiviral

As far back as 1858, Louis Pasteur carried out experiments to confirm the historically recognized bacteria-fighting activity of garlic.⁷ Today garlic is recognized for its ability to fight not only bacteria, but also fungi, viruses and parasites.⁸ The OSCs in garlic appear especially beneficial for limiting the growth and even killing H. pylori, a microbe that commonly infects the stomach and causes ulcers.⁹ Research into the effects of garlic on the immune system show that it can increase the responsiveness of several important antiviral immune cells such as Natural Killer cells and specialized gamma delta T cells.¹⁰ Ultimately the increase in immune cell function has been related to fewer symptoms and reduced severity of cold and flu as well as less time missed from work.¹¹ Besides fighting microbes directly, garlic may serve as a prebiotic, helping to strengthen the good intestinal bacteria so they are better able to fight off infectious agents in the first place.¹² Garlic also reduces the inflammatory compounds that certain microbes produce.¹³

Detoxification

Although much more research is needed to fully understand this connection, the OSCs in garlic are believed to support the body’s detoxification processes. First, OSCs support the detoxification process, helping the body to neutralize and eliminate carcinogens and toxins. Other studies indicate that garlic supplements increase the liver’s levels of glutathione and other important antioxidant enzymes involved in detoxification processes. Furthermore, because many toxic compounds are eliminated from the body through a process known as sulfation, by providing extra sulfur, garlic helps provide substrate to facilitate elimination of harmful compounds by the liver.^{14 15}

Brain Health

The OSCs found in garlic display remarkable utility, benefiting not only the health of the body but also the health of the brain. Some of the most interesting benefits of OSCs include their ability to increase growth of new nervous system tissue, protect the brain from beta-amyloid plaque induced inflammation and damage, and strengthen the blood-brain barrier.^{16 17} Studies in rats that use inflammatory stimuli to impair cognitive function have found garlic supplements are an effective intervention—preventing inflammation from causing brain dysfunction.¹⁸ Other studies show garlic increases the brains natural antioxidant defenses, helps with neurotransmitter signaling, and OSCs act as antioxidants themselves.¹⁹ Overall, there exists a solid body of preclinical evidence suggesting garlic supplements have a promising future as prophylactic treatments for the development of neurodegenerative conditions, such as Alzheimer’s disease.^{20 21}

Other Benefits

Several of the OSCs found in garlic have been investigated for their ability to modulate inflammation.^{22 23} Many of these studies have focused on garlic-related anti-inflammatory effects in the gastrointestinal tract. These studies suggest garlic modulates inflammatory reactions to pharmaceuticals, toxins, and pathogens in the gastrointestinal tract, making it applicable to a large portion of the population.²²

Garlic was used in ancient times to prepare warriors for battle and delay fatigue in laborers, suggesting it may have a unique role as a dietary supplement that benefits athletes. Clinical trials in humans show that OSCs support recovery from exercise through increasing insulin sensitivity, acting as antioxidants, and delaying fatigue in athletes—though much of this appears to occur by enhancing cardiovascular function.

Perhaps nowhere is the line between food and medicine so blurred as it is with garlic. It may be tempting to rely solely on fresh garlic for its many benefits, but the amount needed to reverse an already established condition may be beyond the amount that could be comfortably consumed from food alone. In these cases, a garlic supplement is probably a better choice. Furthermore, the vast majority of studies showing benefits of garlic have focused on garlic supplements rather than fresh garlic. However, as a preventative, the food form is a great option, and it is likely that other beneficial compounds in the diet may react synergistically with those in garlic to produce an even greater effect.²⁴

References

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2. Drake VJ. Garlic and organosulfur compounds. Linus Pauling Institute Oregon State University. http://lpi.oregonstate.edu/infocenter/phytochemicals/garlic/ July 2008. Accessed May 28, 2013.
3. https://www.ncbi.nlm.nih.gov/pubmed/25525386
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