How Garlic Protects Your Heart
This Week’s Research Highlight
Background
Heart disease has maintained its grim distinction as America's leading cause of death since we first began tracking nationwide mortality data in 1933. Today, it claims one in every five lives in the United States.
Through decades of research, we've gained a clearer understanding of what drives cardiovascular disease. At the center of this story is LDL cholesterol. Think of your arteries as smooth highways that blood flows through, while LDL particles are trucks carrying cholesterol cargo. When too many of these trucks crowd the highway, some begin to get stuck in the artery walls, particularly at curves and branches. This buildup, known as atherosclerosis, is the fundamental process behind most heart attacks and strokes.
The evidence for LDL's central role in heart disease is overwhelming, drawing from multiple lines of research. Genetic studies of families with inherited high cholesterol, large population studies tracking hundreds of thousands of people, and clinical trials of LDL-lowering treatments all point to the same conclusion: LDL doesn't just correlate with heart disease — it directly causes it. Moreover, the relationship follows a clear pattern: both the magnitude of LDL elevation and the duration of exposure matter. In other words, the longer your LDL remains elevated, and the higher that it is, the greater your risk becomes.
The good news is LDL is a modifiable risk factor. Notably, what we eat can significantly impact LDL and, consequently, heart disease risk. Nutrition has proven to be astoundingly powerful – in some populations, dietary changes have led to as much as an 80% reduction in cardiovascular deaths. This has led researchers to systematically examine which specific foods might offer the strongest protective effects.
In a recent study, scientists employed an innovative research method called Mendelian randomization to compare 28 different fruits and vegetables. This approach leverages a curious aspect of human genetics – we inherit random variations in genes that influence what we eat. By studying people who are genetically predisposed to eat more of certain foods, researchers can separate true causal relationships from mere correlations.
When the researchers analyzed data from over 400,000 participants, one food jumped out: garlic. People who had genetic variants associated with higher garlic consumption showed significantly lower rates of atherosclerosis. Among all fruits and vegetables studied, garlic demonstrated the strongest causal relationship with heart health.
But why exactly does garlic have this effect? And how can we best take advantage of it?
Inside the Research
To assess garlic's effects on cholesterol, Chinese researchers conducted a comprehensive meta-analysis of clinical trials.
From an initial pool of studies, they applied the following criteria:
- Only randomized controlled trials were included
- Studies had to last at least 2 weeks
- Participants had to have been diagnosed with dyslipidemia (high cholesterol/high triglycerides)
- Garlic had to be the sole intervention (not combined with other treatments)
After this screening process, 21 trials made the final cut.
The selected trials included:
- 1,603 total participants
- Treatment periods from 8 to 36 weeks
- Five different garlic preparations: powder, oil, tablets, raw garlic, and aged garlic extract
- Majority of studies were double-blind
When the researchers crunched the numbers, they found that garlic elicited significant improvements across most measurements:
- Total cholesterol dropped by 25 mg/dL
- LDL cholesterol decreased by 17 mg/dL
- Triglycerides reduced by 15 mg/dL
- HDL cholesterol showed a small increase of 1.5 mg/dL
These are not huge decreases in blood lipids but they are clinically relevant. To put the numbers into perspective, a low dose of pravastatin, (10 mg per day) can lower LDL cholesterol by around 20–30 mg/dL. And even relatively small reductions in LDL, over a long enough time span, can result in substantially lower cardiovascular risk.
This is most powerfully illustrated through analyses that examine the effects of genetic variants that are linked to lower cholesterol levels — in other words, the lifetime impact of reduced exposure to LDL. These sorts of studies have shown that a reduction in LDL of just ~38 mg/dL is associated with more than 50% decreased risk of developing coronary heart disease later in life.
So, long-term consumption of garlic could contribute to better heart health. But how exactly does garlic do this?
The Chemistry Behind Garlic
Garlic improves blood lipids through several key mechanisms.
First of all, garlic reduces cholesterol production, by inhibiting specific enzymes in the liver that are critical to cholesterol synthesis. One such enzyme is HMG-CoA reductase, the very same enzyme that statin medications are designed to target. Garlic also decreases the activity of glucose-6-phosphate dehydrogenase, an enzyme that provides building blocks for cholesterol.
Additionally, garlic enhances the clearance of cholesterol from the body by stimulating bile production. Bile acids bind to cholesterol in the digestive system, preventing it from being absorbed. Furthermore, the process of bile formation itself consumes cholesterol, indirectly lowering the pool of cholesterol in your body.
Beyond simply lowering cholesterol levels, compounds in garlic may prevent oxidative modifications to LDL. When LDL is oxidized, it is more likely to elicit a maladaptive response from the innate immune system. Macrophages engulf the oxidized LDL, and turn into foam cells. These foam cells stick to the artery wall and form fatty deposits, which over time grow into larger plaques. This, by the way, is one reason why eating a diet rich in phytochemicals and antioxidant vitamins is linked to lower risk of heart disease.
Now, let’s talk about the bioactive compounds in garlic that are responsible for these benefits — and what we need to do to harness them.
From Omar, 2013.
The Main Players
In order to understand how garlic works, we need to focus on two sulfur-containing compounds that work in different but complementary ways.
The first star player is allicin.
Inside intact garlic, two substances live in separate compartments: a compound called alliin and an enzyme called alliinase. When you crush or chew the garlic, you break down the cellular walls that keep these components apart, kind of like breaking the barrier in a glow stick. As these substances meet, the alliinase enzyme immediately begins converting alliin into allicin.
This initial reaction happens very quickly — within just a few seconds. However, the allicin that's initially formed isn't stable. It goes through a series of follow-up reactions that create more allicin, as well as other beneficial compounds, which takes some time.
Allicin gives fresh garlic both its pungent aroma and many of its health benefits, but it's highly unstable and reactive — making it powerful but short-lived in the body.
The second key compound is S-allyl cysteine (SAC), which forms through an entirely different process. While fresh garlic contains only tiny amounts of SAC, it does contain precursor compounds called gamma-glutamylcysteines. These precursors gradually convert into SAC when garlic ages in a mixture of alcohol and water for extended periods, typically 20 months or more. This transformation is similar to how grape juice becomes wine — with time and specific conditions creating beneficial compounds that weren't present in the fresh form.
Unlike the volatile allicin, SAC is remarkably stable and water-soluble. This means it can easily circulate through the bloodstream and remain active in the body much longer than allicin. These distinct properties make SAC and allicin perfect complements to each other — one providing immediate, intense effects, the other offering sustained, long-term benefits.
The challenge lies in accessing these compounds, as neither actually exists in high quantities in raw, uncrushed garlic. To harness garlic's full potential, we need to know how to properly prepare it.
How to Get the Most Out of Garlic
To capture both allicin and SAC's benefits, we need to take different approaches. Let's break down exactly how to maximize each compound's availability.
Maximizing allicin from fresh garlic
You want to start with at least two garlic cloves – this is the dose that clinical studies suggest provides cardiovascular benefits, based on alliin content per gram.
(Like a lot of folks, I’m guilty of using a whole lot more than two cloves.)
Crush them thoroughly with a garlic press or mince them very finely with a knife. The goal is to rupture as many cell walls as possible to allow maximum interaction between alliin and the alliinase enzyme.
Now comes the crucial step that most people miss: let your crushed garlic rest for 10-15 minutes at room temperature. During this time, the initial allicin formation triggers a cascade of reactions that generate even more beneficial compounds. This waiting period is non-negotiable if you want to maximize the benefits.
Then, you'll want to consume the garlic relatively soon. If you're cooking with it, add it near the end of preparation, since heat can degrade allicin. Even six minutes of oven heating significantly reduces garlic's beneficial effects.
Accessing SAC through aged garlic
Fresh garlic contains only tiny amounts of SAC precursors (2-6 mg per gram), so it’s not a great source. For reliable SAC intake, supplementation with aged garlic extract is necessary. Kyolic is a well-established brand that standardizes its SAC content through a controlled 20-month aging process. It’s also used in a lot of clinical studies, so you can be sure that it works.
For optimal benefits, consider doing both: consume properly prepared fresh garlic daily for allicin's immediate effects, while also taking a standardized aged garlic extract supplement to maintain steady levels of SAC in your system.
Or, you can take a supplement that combines the two compounds (scroll down for my recommendation).
Random Trivia & Weird News
🧄 While garlic may be great for your heart when eaten, applying it to your skin is decidedly not a pathway to wellness.
The bioactive compounds that make garlic a nutritional powerhouse also make it surprisingly caustic when it comes in direct contact with skin.
A systematic review found 39 cases of people who learned this lesson the hard way, suffering second-degree chemical burns from attempting to use garlic as a topical treatment.
In what must be one of the least successful beauty hacks ever, some patients tried using garlic as an acne treatment. Others wrapped garlic in bandages and left it on overnight, ostensibly hoping for medicinal benefits but instead earning themselves an uncomfortable trip to the emergency room.
Podcasts We Loved This Week
- Jonathan Gruber & David Cutler: Why American health care Is a "broken system." Via Plain English with Derek Thompson.
- Jordan Gass-Pooré: The accidental discovery that gave us “forever chemicals.” Via Science Friday.
Products We Like
Swanson Odor Controlled Garlic
After years of searching around, I think I finally found my go-to product. Based on lab testing, each 500mg capsule delivers potent doses of both allicin and S-allyl cysteine (SAC), and at a much lower price point than the more expensive aged garlic extract products (like Kyolic).
For those who want to reap garlic's proven health benefits, but don't want to eat fresh garlic every day (or deal with its taste and smell), these capsules are a nice solution.
Quick caveat: Garlic contains a melange of compounds which can interact with various medications. It may also increase bleeding risk in vulnerable individuals. If you are going to start supplementing with concentrated garlic, consulting with your physician is a smart idea.
humanOS Catalog Feature of the Week
Heart Health — from The Mediterranean Diet
Interest in garlic and its potential to prevent cardiovascular disease began decades ago, with the observations that people living near the Mediterranean basin were much less likely to develop (or die from) heart disease, and components of their diet appeared to play a key role. Garlic, notably, has been a hallmark of the traditional Mediterranean diet for centuries.
“All around the Mediterranean garlic is used in abundance — in excess Britons might say — and in all that region coronary heart disease is far less common than it is in Britain and northern Europe where garlic is used timidly if at all.”
In this lesson, we dig into some of the diet trials that originally began to unveil how and why the traditional Mediterranean diet is associated with better heart health.
Wishing you the best,
