Evidence: Very High Possible Benefits: Very High Safety: Reasonable
TABLE OF CONTENTS
What is garlic?
Allium sativum, commonly known as garlic, is a popular vegetable sometimes sold in a powdered or capsulated form as a dietary supplement. Like most other vegetables, garlic can reduce inflammation, boost antioxidant defenses, improve cholesterol levels, and more. This article is about the main benefits of garlic, its potential side effects, the best time to take it, and more.
Possible benefits
All of the potential benefits mentioned below are dose-dependent. As with other vegetables, there is a sweet-spot dose that allows you to get most of the benefits without causing meaningful side effects or tolerance buildup in the body. We will discuss the best dosing protocol later in this article.
Major benefits
Reduced rate of sickness – People taking high doses of garlic (2.5 grams of aged garlic or 180 mg of allicin) get common cold 60-70% less often than those who don’t take the vegetable. Garlic can also reduce the symptoms of the common cold and other viral diseases.
Improved cholesterol levels – Garlic was shown in many studies to significantly improve cholesterol levels. In people predisposed to cardiovascular disease, this vegetable increases HDL cholesterol by 10-15%. One meta-analysis shows an improvement of about 1.48 mg/dL. Hypercholesterolemic people also experience reductions of LDL cholesterol of 10-20%. The same applies to total cholesterol. Garlic also seems to somewhat reduce the oxidation of LDL but this effect isn’t overly reliable.
Improved blood flow and blood pressure – Garlic greatly enhances the signaling of nitric oxide. One study found that 2 grams of raw garlic (or about 1 typical clove) can increase nitric oxide by 224% within 2-4 hours of ingestion. A remarkable improvement in blood pressure was found in many studies. On average, garlic seems to reduce blood pressure in hypertensive people by 8-10% or about 10 points (systolic).
Minor benefits
Antioxidant properties – This vegetable contains various antioxidants and can help reduce oxidative stress in the body. Several human studies support that garlic can increase antioxidant enzymes and reduce oxidative stress and DNA damage caused by oxidation.
Reduced inflammation – Like most other vegetables, garlic can reduce chronic inflammation in most people.
Improved immune health – This benefit is secondary to the vegetable’s antioxidant and anti-inflammatory properties. Garlic can improve a wide variety of markers that are correlated to a healthy immune system. For example, it can increase γδ-T cell count by over 700%. Natural killer cell content and activity are also significantly increased by supplementation. Some people, especially those with autoimmune conditions, may experience a temporary worsening of their immune health after they eat or take this vegetable. That is generally nothing to worry about as it’s often just a sign of a hormetic response that helps adapt your body to the vegetable and other stressors.
Lowered blood glucose – While more studies are needed to confirm this benefit, garlic seems to improve blood sugar levels in some people, especially those with insulin resistance or diabetes.
Improved arterial health – Garlic can help prevent excess calcium from stiffening the arteries. Long-term supplementation (for a few years) was shown in one study to reliably reduce arterial stiffness. This vegetable can also notably reduce atherosclerosis, especially in women.
Lowered triglycerides – Supplementation may be somewhat beneficial, especially for people with high triglycerides.
Reduced symptoms of benign prostatic hyperplasia – One study found a 60% reduction in both total and free prostate-specific antigen (PSA) and a 32% reduction in prostatic size after a month of eating 200 mg/kg of garlic.
Reduced hepatopulmonary symptoms – In one study, hepatopulmonary symptoms completely disappeared in two-thirds of the participants after 9-18 months of taking 250 mg of garlic oil daily.
Increased healthspan and lifespan – While the relationship between garlic and healthspan or longevity hasn’t been studied directly, this vegetable has many mechanisms through which it might slow down aging and protect your body from various diseases.
Possible side effects
The side effects below are dose-dependent. The risk for them increases (often linearly but sometimes exponentially) as you increase the dose. Some of the side effects only apply to very high doses.
Bad breath – Allicin in garlic can cause bad breath. This effect is by no means problematic health-wise but it can be unpleasant. Taking aged garlic will not cause bad breath as it doesn’t contain allicin.
Hypotension – High doses of this vegetable or combining it with blood pressure medication may cause your blood pressure to drop too low.
Initial adverse reaction – When you start taking or eating garlic, things can get worse before they get better. This vegetable can temporarily worsen some aspects of your health and even make you sick after taking or eating it. That can be unpleasant, but it is usually a sign that the supplement is working and creating a hormetic response that allows the body to adapt and become more resilient in the long term. People with an autoimmune condition should be careful as the initial adverse reaction may be intense. If you have an autoimmune disease, start with a small dose or amount and gradually build your way up.
Allergic reaction – Some people are allergic to this vegetable and may experience an allergic reaction after they start taking it. Unlike the “initial adverse reaction,” allergic reactions typically don’t disappear until one stops taking or eating the vegetable.
Diarrhea – You can usually prevent diarrhea or stomach discomfort by taking this vegetable with a meal. Taking garlic with food is better regardless because many of the bioactive compounds in the vegetable are fat-soluble.
Toxicity – Some bioactive compounds in garlic, such as allicin, have adaptogenic properties and act as mild stressors on the body. That is usually a great thing as it allows your body to adapt to specific forms of stress and become more resilient. However, stressing the body too much can be counter-productive and cause multiple side effects, including toxicity. While acute toxicity is extremely rare, taking or eating high amounts of this vegetable could lead to chronic toxicity and cause health problems over time. To prevent chronic toxicity or the buildup of tolerance, staying below 6 fresh cloves or 1200 mg of a dry powder in a day is best unless you have a great reason to take more.
Contamination – If growing or storing conditions are not adequately controlled, garlic can be contaminated with bacteria, molds, and other potentially harmful microorganisms. Many growers also use pesticides that can be unsafe. Choose the brand you get vegetables and vegetable supplements from wisely. For vegetable supplements, it is often best to use websites like Amazon, where thousands of users have reviewed and rated the products. You are less likely to buy something of lower quality there.
Who should not eat or take garlic?
You should probably avoid garlic if you:
experience hypotension
are allergic to this vegetable
experience a severe adverse reaction after taking or eating the vegetable (though a mild adverse reaction is usually a great thing as it is a sign that the adaptogenic molecules in the vegetable are working and causing a hormetic response that allows the body to adapt and become more resilient)
have an autoimmune condition that makes your immune system overreact to xenohormetic stressors (you can eat or take this vegetable in that case, but it’s best to start with low amounts)
Who will benefit the most?
You should consider taking the vegetable or adding it to your diet if you:
often get sick
have high blood pressure
experience heart problems
have unhealthy cholesterol levels
experience symptoms of benign prostatic hyperplasia
wish to improve general health
have a high budget for supplements and are willing to experiment with a variety of them (assuming you don’t fall into any of the categories that should avoid this vegetable, garlic appears safe and is unlikely to do more harm than good for most people)
Black garlic vs. normal garlic
Just like normal garlic, black garlic (also known as aged garlic) comes from the Allium sativum plant. Black garlic is regular garlic that has been fermented for about a month. The fermentation process changes the color, texture, taste, and chemical composition of garlic cloves.
The main difference between fresh and black garlic as far as health goes is that allicin, one of the main bioactive compounds in garlic, gets converted into several other compounds, such as diallyl disulfide, diallyl trisulfide, and S-allylcysteine (SAC).
Since allicin is the compound in garlic with the highest potential for toxicity, black garlic is much safer in high amounts than fresh garlic. Allicin is also responsible for the smell of garlic. Because it gets broken down during the fermentation process, black garlic doesn’t cause bad breath.
As far as the benefits, regular and black garlic are roughly equal. Black garlic generally has higher levels of antioxidants and may be slightly more beneficial but the difference isn’t that big.
How much garlic should you take?
Because garlic contains adaptogenic compounds, it acts as a mild hormetic stressor on the body, which allows your body to adapt and become more resilient to certain kinds of stressors in the long term. A higher dose of these adaptogens isn’t necessarily better because they may stress out the system too much.
The sweet-spot dose typically ranges anywhere between 3-4 average freshcloves or 600-1200 mg of dry powder daily. The optimal dose for aged (black) garlic is also about 600-1200 mg.
If you purchase an extract standardized for allicin, the sweet spot dose of allicin is about 30-70 mg.
The higher end of this range usually provides slightly more benefits in the short term. If you plan to take or eat this vegetable regularly for a longer time (multiple months or years), the lower end is probably a better way to go.
You would develop tolerance to the xenohormetic molecules faster if you took or ate higher amounts. Additionally, very high doses can put too much pressure on your system and cause health problems if you take the supplement for a prolonged period.
While this vegetable could theoretically cause acute toxicity, you’d need to take an extremely high amount that would be way beyond what even the most potent supplements contain.
Like most other plants, it is best to cycle garlic and take about two days off weekly to reset your tolerance to the adaptogenic and xenohormetic compounds in it. That will allow you to keep getting the benefits in the long term.
Best time to take garlic
Some of the main bioactive compounds in this vegetable are fat-soluble, so you want to take it with food or a dietary source of fat.
Whether you take this vegetable in the morning or the evening does not make much difference. Both options are fine so feel free to experiment.
Interactions
Nitrate Nitrate is a chemical found in high amounts in some vegetables, such as beetroot and spinach. In the body, nitrate can convert into nitric oxide, which can improve blood flow and cardiovascular health. Garlic enhances the signaling of nitric oxide, further increasing this positive effect.
Cocoa Cacao helps maintain nitric oxide levels elevated by nitrate high. This means that garlic can keep increasing the signaling of nitric oxide for longer.
Blood pressure medications This combination may cause your blood pressure to drop too low.
Where to buy garlic supplements?
In most countries, Amazon is the best option for ordering garlic and other vegetable supplements. They offer some very affordable products backed by many positive reviews. Also, you can choose from a wide range of brands without having to search through other markets on the Internet.
Some brands display the dosage per serving instead of per pill or capsule. Therefore, you may accidentally buy something less potent than you intended. Do not fall for this marketing trick.
FAQ
As with most other vegetables and vegetable supplements, it is best to cycle garlic and take a break from it for about two days per week to reset your tolerance back to baseline. That will keep your body sensitive to the vegetable and allow you to keep getting the benefits in the long term.
Eating a fresh vegetable is almost always better as it contains many beneficial compounds that get lost during drying or extraction. On the other hand, supplements and dry powders don’t go bad nearly as fast as fresh vegetables, don’t need to be stored in perfect conditions, and are often cheaper. Also, black garlic is commonly sold in capsules and is much safer and just as beneficial if not more beneficial than regular garlic.
This vegetable by itself should not worsen your sleep quality in any way. However, it’s best to take it with food, and you generally don’t want to eat any food right before bed as it could worsen your digestion and sleep quality.
Dry vegetable powders and supplements can expire but not nearly as fast as fresh vegetables. They can also lose potency over time but very slowly if you store them well. Keep the supplement in a cold, dark, and dry place. It should remain just as potent for many months or even years there.
Yes. Garlic contains adaptogenic and xenohormetic compounds that act as mild stressors on the body. That is usually a great thing as it allows your body to adapt to specific forms of stress and become more resilient. However, stressing the body too much can be counter-productive and cause multiple side effects, including toxicity. While acute toxicity is extremely rare, taking or eating very high amounts of this vegetable could lead to chronic toxicity and cause health problems over time. High doses can also make you develop tolerance much faster than lower doses, and they may be less effective at improving health in the long term.
While you could safely take higher doses, there is usually no point in eating more than 4 fresh cloves or 1200 mg of a dry powder daily. This amount should give you most of the benefits without meaningful side effects. The only exception is if this vegetable is helping you fix a nutrient deficiency, in which case you may want to take more of it.
The half-life of the main bioactive compounds in garlic in the body is anywhere from 30 minutes to 6 hours. The biggest increases in blood flow typically occur within 3-4 hours after ingestion. Besides an increase in nitric oxide and blood flow, most of the effects of this vegetable are cumulative, so they mostly happen in the long term rather than acutely. Therefore, the half-life of this vegetable isn’t very relevant in practice.
Eating this vegetable would break a fast and reduce some benefits of it. Taking garlic supplements would probably have little to no effect on fasting.
References
Most of the information in this guide is based on scientific research that can be found and verified in the PubMed medical library. We highly encourage you to use the library to verify anything you read in this article. We excluded from consideration studies that are either confounded or have a high conflict of interest.
