What Is Glycine?

Glycine is one of the many amino acids your body needs to function properly. Glycine is important because it:

• Stimulates production of the "feel good" hormone serotonin
• Serves as the key component of collagen, a protein that gives structure to bones, skin, muscles, and connective tissues, as well as other key proteins
• Plays a role in nerve signal transmission and clearing toxins from the body

Glycine may also benefit the following, though evidence is limited and more research is needed:

• Mood and memory
• Sleep
• Stroke recovery
• Heart disease
• Certain psychiatric disorders, such as schizophrenia

Unlike some amino acids that must be obtained solely through foods, the body can produce glycine. It is also available in supplement form.

This article looks at glycine supplements' potential benefits and risks and whether the current science supports the health claims. It also offers tips on how to select and use glycine supplements safely.

Uses of Glycine

Glycine use should be individualized and vetted by a healthcare professional, such as a registered dietitian, pharmacist, or doctor. No supplement is intended to treat, cure, or prevent disease. 

Glycine is an amino acid that serves as a building block for specific proteins, including collagen, a structural protein found in connective tissues. Collagen is found in:

• Skin
• Ligaments
• Muscles
• Bones
• Cartilage

Glycine also helps regulate nerve impulses in the central nervous system. This system affects the spinal cord and the brain. Glycine also binds to toxins so that the body can clear them.

In addition to the glycine already produced by the body, you can also take glycine supplements. Most current research has focused on glycine's role in sleep, mood, stroke, and heart disease.

Mood and Memory

Glycine stimulates the production of serotonin, the "feel-good" hormone that helps elevate mood, improve sleep, and enhance memory and thinking.

Studies on rodents have demonstrated that glycine supplementation increases serotonin levels. Due to these effects, some people tout glycine supplements as "natural antidepressants." However, their impact on the brain appears to be short-lived, often dissipating within minutes.

For example, in a 2011 study in Psychiatry and Clinical Neurosciences, researchers measured serotonin levels in rats after glycine administration. They found that serotonin increased for only 10-20 minutes after glycine supplementation compared to more than 180 minutes after receiving a selective serotonin reuptake inhibitor (SSRI), an antidepressant medication.

Sleep

Some research suggests that glycine supplements may improve sleep in people with insomnia. For example, a 2015 study from Japan evaluated why sleep improved in rats after glycine supplementation. To assess the effects, researchers implanted a telemetry unit on the animals. After recovery, rats were given either glycine or water.

Those who received glycine had significantly decreased wakefulness and increased non-rapid-eye-movement (NREM) sleep during the first 90 minutes compared with the control group. Researchers concluded that glycine promotes sleep because it alters body temperature and circadian rhythms.

Again, scientists did this research on animals, and therefore it is uncertain whether these results would translate to humans.

In a 2012 human study, researchers evaluated glycine's effects on daytime performance in sleep-restricted participants. In the randomized single-blinded crossover trial, seven healthy adults without sleep disorders had their time in bed reduced by 25% for three nights. They were then given 3 grams of glycine or a placebo 30 minutes before bed.

Participants rated their daytime sleepiness, fatigue, and performance. Glycine significantly improved fatigue feelings, reduced sleepiness, and improved performance compared to the placebo group.

Schizophrenia

Researchers have looked at how glycine might treat schizophrenia, a mental illness that causes delusions, hallucinations, and unusual behavior.

In a 2016 review of studies, researchers found conflicting evidence about glycine's effect on schizophrenia. For example, while some studies reported that glycine supplements taken with antipsychotics reduced the incidence of cognitive side effects, others showed no difference compared to placebo groups. In addition, researchers observed that people needed a relatively high dose to see any results.

Ischemic Stroke

Healthcare providers sometimes prescribe glycine to people who have just had an ischemic stroke. Ischemic strokes occur when the arteries to the brain become narrowed or blocked, causing blood flow restriction (ischemia) in the brain. The evidence supporting the use of glycine for this is mixed.

Early research published in 2000 in Cerebrovascular Disease looked at the protective effects of glycine after an ischemic stroke. In the randomized, double-blind, placebo-controlled trial, researchers divided 200 participants who had an ischemic stroke in the carotid artery into groups:

• Glycine of 0.5 g/day
• Glycine of 1.0 g/day
• Glycine of 2.0 g/day
• Placebo

The participants received glycine or a placebo for five days. Those who received 1-2 grams of glycine had a decreased 30-day mortality compared to the other groups. Researchers concluded that a sublingual (under the tongue) dose of glycine given within six hours of a stroke could limit the damage done to the brain.

However, a 2015 population study from Japan looked at glycine and stroke mortality in 29,079 Japanese adults. According to the survey, a high-glycine diet raised the systolic blood pressure (the higher number in a blood pressure reading) to such a degree in men that it increased the risk of death from stroke. The same was not seen in women.

This study contradicts the earlier study, indicating that high amounts of glycine might increase the risk of death from stroke, at least in some people.

Heart Disease

Glycine is anti-inflammatory and antioxidative (meaning it prevents or slows cell damage), which are properties that reduce heart disease risk. Therefore, some researchers have looked at the connection between glycine and heart disease.

In a 2015 study in the Journal of the American Heart Association, researchers looked at the association between glycine plasma levels and acute myocardial infarction (heart attack). This population study evaluated 4,109 people who had elective coronary angiography to diagnose stable angina (a blockage in the coronary artery).

The study found that those with higher plasma glycine levels had a more favorable heart disease risk profile and a decreased risk of a heart attack.

While the study is promising, research on the topic is limited.

Other

In addition to the potential health benefits listed above, some people use glycine to support:

• Enlarged prostate
• Leg ulcers
• Liver damage
• Insulin resistance and type 2 diabetes

What Are the Side Effects of Glycine?

Your healthcare provider may recommend you take glycine to support your sleep or mood or lower your heart disease or stroke risk. However, consuming a supplement like glycine may have potential side effects.

Common Side Effects

Glycine supplements are generally considered safe if used as directed. However, there has been little research into the long-term safety of glycine supplements.

Most people who take glycine will not experience any side effects, but some may have gastrointestinal symptoms such as:

• Upset stomach
• Nausea
• Diarrhea
• Vomiting

Precautions

Since studies have found that glycine supplements interact with antipsychotic drugs, like Clozaril (clozapine), you should talk to a healthcare provider before taking glycine if you are taking these medications. As a general rule, it's best to speak to a healthcare provider before trying any new medications or supplements.

In addition, unless instructed by a healthcare provider, the following people should avoid glycine:

• Children
• Those who are pregnant
• Those who are breastfeeding

It is essential to carefully read the ingredient list and nutrition facts panel of a supplement to know which ingredients and how much of each ingredient is included. In addition, please review this supplement label with your healthcare provider to discuss any potential interactions with foods, other supplements, and medications. 

Dosage: How Much Glycine Should I Take?

Glycine is available in several different formulations. The most common is oral gel caps, typically available in 500 milligrams (mg) to 1,000 mg doses. There are also powdered formulations that you can add to shakes or smoothies.

There are no guidelines for the appropriate use of glycine in people with schizophrenia. But, some research is based on a dosage of 0.4 grams per kilogram of body weight (g/kg) twice daily when taking an atypical antipsychotic like Zyprexa and Risperdal. However, always discuss glycine supplementation and dosage with a healthcare provider first.

Topical creams containing glycine and the amino acids L-cysteine and DL-threonine are available by prescription for leg ulcers. Depending on the circumstance, they may be prescribed once daily, twice daily, or every other day.

What Happens If I Take Too Much Glycine?

Glycine toxicity from supplements is rare. However, it can occur when used with sterile water for bladder irrigation. In this situation, a healthcare provider administers glycine, usually after prostate or bladder surgery, to prevent or flush out blood clots.

Signs of glycine toxicity include:

• Visual disturbances
• Drowsiness
• Vomiting
• Weakness
• Prickling skin sensations
• Skin flushing
  

Glycine toxicity can be fatal.

How to Store Glycine

Store glycine supplements and powders in a cool, dry place. Never use a supplement that is expired or appears damaged or discolored. Speak with a healthcare provider before using any supplement for medical reasons.

Sources of Glycine and What to Look For

Glycine is readily available in plenty of foods. You can also take it in supplement form.

Food Sources of Glycine

You can find glycine in high-protein foods. Good sources of glycine-rich foods include legumes, fish, dairy, and meat.

Among the best food sources of glycine are:

• Red meat: (1.5 to 2 g per 100 g serving)
• Seeds (1.5 to 3.4 g per 100 g)
• Turkey (1.8 g per 100 g)
• Chicken (1.75 g per 100 g)
• Pork (1.7 g per 100 g)
• Peanuts (1.6 g per 100 g)
• Canned salmon (1.4 g per 100 g)
• Granola (0.8 g per 100 g)
• Quinoa (0.7 g per 100 g)
• Hard cheese (0.6 g per 100 g)
• Pasta (0.6 g per 100 g)
• Soybeans (0.5 g per 100 g)
• Bread (0.5 g per 100 g)
• Almonds (0.6 g per 100 g)
• Eggs (0.5 g per 100 g)
• Beans (0.4 g per 100 g)
  
  

Glycine Supplements

Glycine supplements come in capsules or powder formulations. Some people prefer capsules because they are easy to take. Others enjoy incorporating powders into shakes or smoothies.

Supplements are typically vegetarian or vegan. However, read the label carefully for allergens like wheat or eggs if you have food allergies.

Summary

Glycine is an amino acid produced by the body that is important for building collagen, transmitting nerve impulses, and clearing toxins from the body. Some people contend that glycine supplements can enhance many of these functions and, in turn, prevent or treat certain medical conditions.

To date, the evidence of this is weak. Despite claims to the contrary, there is little evidence that glycine supplements can prevent diabetes, relieve insomnia, heal wounds, treat an enlarged prostate, or reduce the risk of death from stroke. They may reduce the risk of side effects from certain schizophrenia medications, but more research is needed.

Glycine supplements are generally considered safe but may cause diarrhea, nausea, upset stomach, and vomiting. Speak with your doctor before using supplements for any medical reason.