From tackling the common cold to fighting chronic disease, garlic is a bona-fide health food hero.
Medically reviewed by Dr Roger Henderson and words by Annie Hayes
One of the oldest cultivated plants in the world, garlic is a culinary staple in kitchens across the globe. This is mostly due to its mouth-watering flavour – seriously, where would we be without garlic bread? – as well as its many health benefits, which range from tackling the common cold to fighting the common causes of chronic diseases.
Though widely used as a herb or spice, botanically-speaking, garlic is a vegetable. It belongs to the onion family, alongside leeks, chives, spring onions, shallots, and other pungent plants. When the cloves are cut, crushed or chewed they release sulphur compounds such as allicin, which are believed to be responsible for its health-giving properties.
We asked clinical pharmacist and nutritionist Mike Wakeman of Vitmedics to talk us through the health benefits of garlic:
12 proven health benefits of garlic
Historically, garlic was prescribed as a medicine – in fact, it was one of the most important medicinal herbs used in ancient times, says Wakeman.
‘It’s used as a remedy against common wellness troubles as well as serious health problems, from colds and influenza to helping to reduce the risk of diabetes and cardiovascular diseases,’ he says. ‘Raw garlic contains various sulphur compounds, including allicin – thought to be the most biologically active compound.’
As the science attests, garlic is a bona-fide health food hero. Here, we run through its most potent evidence-backed health benefits:
- Garlic is highly nutritious
Despite its small size, a clove of garlic is incredibly nutritious. Garlic is particularly rich in vitamin C, vitamin B6 and manganese, and also contains vitamins A, B1, B2, B12, D and E, as well as the minerals calcium, copper, iron, phosphorus, potassium and selenium.
Each clove contains approximately:
- 4 calories
- 2 grams of protein
- 1 gram of carbohydrates.
Each clove contains approximately four calories, 0.2 grams of protein and one gram of carbohydrates.
- Garlic is packed with sulphur compounds
The unique flavour of garlic comes from sulfur compounds. Like other members of the onion family, the plant absorbs sulfate from the soil and stores it in molecules. When we prepare and eat garlic, these sulfur molecules break down into approximately 50 different compounds that interact with certain molecules in the body, and have been observed to exert powerful biological effects. While scientific research into these compounds is ongoing, they are believed to be responsible for many of garlic’s health benefits.
- Garlic helps fights bacteria
Thanks to its antimicrobial properties, garlic has been used for centuries to combat infectious disease, says Wakeman. ‘More recently, garlic has been proven to be effective against a plethora of bacteria,’ he says. ‘These include Salmonella, Escherichia coli, Pseudomonas, Staphylococcus aureus, and Helicobacter.’
- Garlic supports your immune system
Garlic has antiviral properties, and could help combat sickness – including the common cold. ‘Studies have reported that garlic extract showed activity against influenza A and B, rhinovirus, HIV, herpes simplex viruses, viral pneumonia, and rotavirus,’ says Wakeman.
‘A placebo controlled single trial suggests that garlic may prevent occurrences of the common cold, but more studies are needed to validate this finding,’ he continues. ‘The investigation revealed lower incidence of common cold in the garlic group compared with the placebo group, resulting in fewer days of illness. More quality evidence is needed.’
- Garlic is a potent antioxidant
Garlic contains antioxidants, which are substances that help to protect our cells against oxidative damage caused by free radicals. Oxidative damage has been linked to diseases such as heart disease, cancer, arthritis, stroke, and also contributes to the ageing process.
‘Free radicals are molecules produced when your body breaks down food or when you’re exposed to tobacco smoke or radiation,’ says Wakeman. ‘Garlic extract has been found to increase the activities of some antioxidant enzymes – hence research suggests it could contribute to its anti-ageing benefits.’
- Garlic possesses anti-inflammatory activity
While inflammation plays a vital role in healing, chronic inflammation increases the risk of a number of serious diseases, including certain cancers, rheumatoid arthritis, diabetes, and cardiovascular disease. ‘Garlic extracts and its compounds have also been shown in research to possess anti-inflammatory activity,’ says Wakeman.
‘It is suggested that garlic’s potent antioxidant activities may be responsible for its anti-inflammatory activity, but there is also evidence that garlic extracts can directly prevent production of compounds involved in the inflammatory process,’ he adds.
- Garlic lowers heart disease risk
Consuming garlic can help to lower your risk of cardiovascular diseases, such as heart disease and stroke, in several ways. Garlic supplements have a significant impact on reducing blood pressure in people with high blood pressure, human studies have shown.
‘Studies show the essential function of garlic in the control of cardiovascular risk factors, as it is known to significantly decrease systolic as well as diastolic blood pressure,’ says Wakeman. ‘Garlic contains many active sulphur molecules that have been shown to directly affect the relaxation of blood vessels leading to lower blood pressure.’
Garlic supplements have a significant impact on reducing blood pressure in people with high blood pressure.
Garlic also reduces your levels of ‘bad’ LDL cholesterol. ‘Evidence suggests that garlic preparations might reduce harmful cholesterol levels by preventing their biosynthesis in the liver, as well as inhibiting LDL and HDL oxidation, which is thought to contribute to the harmful effects of cholesterol,’ he adds.
Furthermore, a study by Los Angeles Biomedical Research Institute found that supplementing with aged garlic extract reduces the accumulation of certain types of plaque in the arteries, another risk factor for heart disease.
- Garlic may prevent Alzheimer’s and dementia
Not only can garlic help to improve cognitive health in the elderly, but studies suggest it may even reduce the risk of common brain diseases like Alzheimer’s disease and dementia. In a rodent study by the University of Louisville, supplementing a garlic compound – a suphur compound called allyl sulfide – was shown to counteract age-related changes in gut bacteria associated with memory problems.
‘Garlic has been identified to have beneficial effects on some of the processes that appear to be defective in Alzheimer’s, most notably involving the neurotransmitter acetylcholinesterase in the nervous system,’ says Wakeman. ‘One study reported that the prolonged garlic uptake is related to promoting the memory function by affecting the levels of another neurotransmitter, serotonin.’
- Garlic reduces blood sugar levels
Garlic is antidiabetic, which means it can help a person with diabetes control their blood sugar (glucose) levels. This is due to its effect on insulin, a hormone made in the pancreas that helps your body use glucose for energy.
‘The sulphur compounds in garlic have been shown to decrease the blood glucose level by preventing the insulin activation caused by the liver, enhancing the secretion of insulin from the pancreas and increasing the cell sensitivity to insulin,’ says Wakeman.
- Garlic promotes gut health
Being both antibacterial and prebiotic, garlic delivers a one-two punch for great gut health. A prebiotic is a type of non-digestible fibre that feeds healthful bacteria in the gut. Garlic contains inulin and fructooligosaccharides, which promote the growth of beneficial Bifidobacteria, while at the same time preventing disease-promoting bacteria from growing due to its antibacterial properties. ‘Research has documented that garlic exerts a differential inhibition between beneficial intestinal microflora and potentially harmful enterobacteria,’ says Wakeman.
- Garlic may reduce cancer risk
Laboratory tests have shown that the compounds in garlic can kill off cancer cells, but as yet, there are no studies that measure garlic’s potential anti-cancer effects in humans. However, an umbrella review of existing research conducted by scientists in China found that regular consumption of garlic and other allium vegetables is linked to a reduced risk of several types of cancer, including of the stomach, throat, prostate and colon. The most beneficial cancer-related outcome was shown for gastric cancer.
- Garlic improves bone health in women
While more research is certainly needed, garlic appears to have some benefits for bone health by increasing estrogen levels in women. Rodent studies have shown that supplementing with garlic can minimise bone loss by increasing estrogen levels. And in a study of menopausal women by Shahid Sadoughi University of Medical Sciences, taking dry garlic extract ‘significantly’ decreased estrogen deficiency. And among the general population, high consumption of allium vegetables is associated with protection against hip osteoarthritis, according to a cross-sectional UK study.
Garlic side effects and precautions
Potential garlic breath aside, consuming garlic in moderation is generally safe. However, some people may need to be a little more cautious, especially when using garlic capsules or supplements, since they may interact with certain medicines, e.g. blood thinning medication. Additionally, you should avoid taking garlic supplements two weeks prior to surgery. This is because high doses of garlic may inhibit blood clotting and consequently increase the risk of bleeding. If you have any concerns, consult your doctor or pharmacist.