Glycine

Medically reviewed by Prof. Giorgi Pkhakadze, MD, MPH, PhD — GMJ Editorial Board

What is Glycine?

Glycine is the smallest and simplest amino acid, consisting of just two carbon atoms, one nitrogen atom, and five hydrogen atoms. As one of the 20 standard amino acids used to build proteins, glycine is classified as “conditionally essential,” meaning the body can produce it internally but may require dietary sources during periods of stress, illness, or rapid growth. Unlike other amino acids, glycine lacks a side chain, making it unique in its ability to fit into tight spaces within protein structures.

The body synthesizes glycine primarily in the liver from serine, threonine, and choline. It serves multiple critical functions beyond protein synthesis, including neurotransmitter activity, collagen production, and cellular detoxification processes. Glycine constitutes approximately one-third of the amino acids in collagen, making it essential for skin, joint, and connective tissue health.

Health benefits & uses

Sleep Quality (Moderate evidence): Clinical studies demonstrate that glycine supplementation can improve sleep quality and reduce sleep latency. Research shows 3 grams of glycine taken before bedtime enhances subjective sleep quality and reduces daytime sleepiness. The amino acid appears to lower core body temperature and modulate circadian rhythms through its action on NMDA receptors.

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Collagen Synthesis (Moderate evidence): As a primary component of collagen, glycine supports skin elasticity, joint health, and wound healing. Studies indicate that glycine supplementation may enhance collagen production, though most research combines it with other amino acids like proline and hydroxyproline.

Cognitive Function (Limited evidence): Some research suggests glycine may support memory and cognitive performance through its role as an inhibitory neurotransmitter. However, human studies are limited, and more research is needed to establish definitive cognitive benefits.

Blood Sugar Control (Limited evidence): Preliminary studies indicate glycine may help improve insulin sensitivity and glucose metabolism, but evidence remains insufficient for therapeutic recommendations.

How it works

Glycine functions through multiple mechanisms in the body. As an inhibitory neurotransmitter, it binds to glycine receptors in the brain and spinal cord, promoting relaxation and supporting sleep. In the central nervous system, glycine also acts as a co-agonist at NMDA receptors, which are crucial for learning and memory.

For collagen synthesis, glycine provides the structural foundation for the characteristic triple-helix structure of collagen proteins. Every third amino acid in collagen chains is glycine, allowing the tight packing necessary for collagen’s strength and flexibility.

Glycine also supports detoxification by conjugating with various compounds in the liver, making them more water-soluble for elimination. Additionally, it serves as a precursor for important molecules like creatine, glutathione, and heme, the oxygen-carrying component of hemoglobin.

Dosage

No official RDA or UL has been established for glycine. Typical supplemental dosages vary based on intended use:

• Sleep support: 3 grams taken 30-60 minutes before bedtime
• General health: 1-3 grams daily with meals
• Collagen support: 3-10 grams daily, often combined with vitamin C

Most research uses dosages between 3-10 grams daily, well-tolerated by healthy adults. Start with lower doses and gradually increase as needed. Consult with a healthcare provider before beginning supplementation, especially for therapeutic purposes or if you have underlying health conditions.

Food sources

Glycine is found in protein-rich foods, with the highest concentrations in:

• Animal proteins: Bone broth, gelatin, chicken skin, pork skin
• Meat: Beef, pork, chicken, turkey
• Seafood: Fish, shellfish, especially skin and bones
• Dairy: Milk, cheese, yogurt
• Plant sources: Soybeans, sesame seeds, sunflower seeds, spinach

Bone broth and gelatin are exceptionally rich sources, containing 1-3 grams of glycine per serving. Traditional diets with nose-to-tail eating provided significantly more glycine than modern diets focused on muscle meats.

Safety & side effects

Glycine supplementation is generally well-tolerated with few reported adverse effects. Most people can safely consume up to 10 grams daily without issues. Potential side effects are rare but may include:

• Mild gastrointestinal upset
• Nausea at high doses
• Drowsiness (particularly when used for sleep)

Glycine has been granted GRAS (Generally Recognized as Safe) status by the FDA. Long-term safety data is limited, but the amino acid’s natural presence in foods and endogenous production suggest minimal risk for healthy individuals.

Interactions

Medications: Glycine may enhance the effects of sedative medications, including benzodiazepines, sleep aids, and alcohol. Use caution when combining glycine with any central nervous system depressants.

Supplements: Glycine works synergistically with other amino acids involved in collagen synthesis, particularly proline and vitamin C. It may also complement magnesium and melatonin for sleep support. No significant negative interactions with other supplements have been reported.

Timing considerations: Take glycine away from high-protein meals if using for sleep, as competing amino acids may reduce absorption and effectiveness.

Who should be cautious

While generally safe, certain groups should exercise caution with glycine supplementation:

• Pregnant and nursing women: Insufficient safety data during pregnancy and lactation
• Children: No established pediatric dosing guidelines
• Individuals with kidney disease: May need to monitor protein and amino acid intake
• People taking psychiatric medications: Potential interactions with mood-altering drugs
• Those with bleeding disorders: Limited data on effects on blood clotting

Always consult healthcare providers before starting supplementation, especially if you have medical conditions or take medications.

Frequently asked questions

When is the best time to take glycine?

For sleep support, take glycine 30-60 minutes before bedtime on an empty stomach. For general health benefits, glycine can be taken with meals throughout the day to minimize any potential stomach upset.

Can I get enough glycine from food alone?

Most people consuming a varied diet with adequate protein intake produce sufficient glycine for basic needs. However, modern diets often lack glycine-rich foods like bone broth and organ meats, potentially creating suboptimal levels for therapeutic benefits.

How long does it take to see benefits from glycine?

Sleep benefits may be noticed within 1-3 days of consistent use. Skin and joint benefits from collagen support typically require 4-12 weeks of regular supplementation to become apparent.

Is glycine safe for long-term use?

Current evidence suggests glycine is safe for long-term use at recommended dosages. However, long-term studies are limited, so periodic breaks or healthcare provider monitoring may be prudent for extended supplementation.

Can glycine help with anxiety?

Some people report calming effects from glycine due to its role as an inhibitory neurotransmitter. However, research specifically examining glycine for anxiety is limited, and it should not replace proven anxiety treatments without professional guidance.