From heart health to drug interactions: garlic’s effect on the body

Whether it is sizzling in olive oil or crushed into a curry, garlic has long been a hero in the kitchen. But beyond its strong flavour, garlic has earned a reputation as a natural remedy with a surprising range of potential health benefits. From heart health to immune support, science increasingly supports what tradition has claimed for centuries: garlic is good for you.

The secret lies in its chemistry. Garlic (allium sativum) contains sulphur compounds, including diallyl disulfide and S-allyl cysteine, that are responsible for both its distinctive smell and its medicinal effects.

The most studied of these is allicin, which forms when garlic is chopped, crushed or chewed. Allicin is unstable and quickly breaks down into other sulphur-containing compounds that are linked to several health effects. Here are some of the best supported benefits.

1. Heart health

Garlic is widely studied for its potential to support the heart and blood vessels. Garlic supplements can help reduce high blood pressure, with some studies finding effects similar to certain prescribed medications. A 2019 analysis found that garlic supplements significantly lowered blood pressure in people with hypertension. This reduction was linked to a 16%-40% lower risk of cardiovascular events, such as heart attacks and strokes.

Research suggests this may be because garlic extract improves arterial elasticity so that arteries become more flexible, helping them expand and contract more easily as blood flows through. Stiff arteries make the heart work harder and are a risk factor for heart disease.

Garlic compounds also appear to help relax blood vessels by increasing levels of hydrogen sulphide and nitric oxide. These are gases naturally produced in the body that help blood vessels widen so blood can flow more easily. Allicin may also help reduce blood pressure by blocking angiotensin II, a hormone that causes blood vessels to tighten.

Research suggests garlic may also lower total cholesterol – the overall amount of cholesterol in the blood – and LDL cholesterol, often called bad cholesterol because high levels can clog arteries. Some studies show that taking garlic for longer than two months can reduce LDL cholesterol by up to 10% in people with mildly raised levels.

Lab studies show that garlic compounds can block liver enzymes that produce fats and cholesterol. They may also prevent plaque building up in the arteries by reducing LDL and making it more resistant to oxidation, a process that contributes to heart disease.

2. Immune support

The antibacterial effects of allicin are well recognised. Garlic extract has also been shown to have antimicrobial activity against bacteria, viruses and fungi.

One study found that people who took aged garlic extract had milder cold and flu symptoms, recovered more quickly and missed fewer days of work or school.

More recent research suggests garlic may support the immune system by activating certain types of white blood cells. These include macrophages, which are immune cells that engulf and destroy bacteria and viruses; lymphocytes, which include T cells and B cells that recognise infections and produce antibodies; and natural killer cells, which target and destroy infected or abnormal cells such as virus infected or cancerous cells.

Garlic may also help regulate inflammation, which is a key part of the immune response.

3. Cancer prevention

Early research suggests garlic may help reduce the risk of certain cancers, particularly those affecting the digestive system, colon, lungs and urinary tract.

A study found that garlic can affect key processes involved in cancer development. It may stop cancer cells from dividing, prevent the formation of new blood vessels that feed tumours and encourage cancer cells to die naturally. These effects appear to be linked to garlic’s influence on cell signalling pathways which control how cells grow and behave. Garlic’s antioxidant and anti-inflammatory properties may also contribute.

However, most of this evidence comes from laboratory and animal studies which do not always apply to humans. More robust clinical studies on people are needed.

Garlic has also been linked to other possible health benefits although research is still ongoing. Its antioxidant effects may help lower the risk of Alzheimer’s disease, and its anti-inflammatory properties may be useful in conditions such as osteoarthritis.

How much garlic is enough

There is no official recommended daily amount for garlic. Many studies use the equivalent of one to two cloves per day. Supplements are also widely available. Eating garlic as part of food provides fibre, vitamins and other plant compounds that supplements do not contain so food sources may offer extra benefits beyond supplements alone.

Garlic is generally safe but it can cause bloating, gas and heartburn especially when eaten raw or in large amounts. People with irritable bowel syndrome, acid reflux or those who are pregnant may be more sensitive.

Garlic is also known for causing bad breath and body odour. As allicin breaks down, it releases sulphur containing gases. Most are processed by the body but one called allyl methyl sulphide remains unmetabolised and leaves the body through breath and sweat.

Garlic can interact with certain medications if taken in large amounts. It may increase the effects of aspirin or blood-thinning medicines such as warfarin which can increase the risk of bleeding. Garlic may also lower blood pressure which could be a problem for people already taking medication for high or low blood pressure. Those who are pregnant or breastfeeding should be cautious because high-dose garlic supplements have not been well studied, so the effects on the developing baby or infant are not fully known.

Garlic is more than a flavour booster. It is a functional food with a growing body of scientific evidence behind it. While it is not a replacement for medical treatment, including garlic in your diet may offer real benefits for your heart and immune system.

Whether you roast it, crush it or take it as a supplement, garlic deserves a place in your health routine. If you take medication or have existing health conditions speak to a doctor or pharmacist before using garlic in large amounts. As with any natural remedy, moderation is important.

This article is republished from The Conversation, a nonprofit, independent news organization bringing you facts and trustworthy analysis to help you make sense of our complex world. It was written by: Dipa Kamdar, Kingston University

Dipa Kamdar does not work for, consult, own shares in or receive funding from any company or organisation that would benefit from this article, and has disclosed no relevant affiliations beyond their academic appointment.