Inhaltsstoff-Glossar

Glycine

What Is Glycine?

Glycine is the simplest proteinogenic (protein-forming) amino acid found in nature. It is considered conditionally non-essential because the human body is able to synthesize it, although endogenous production alone is insufficient to meet the body's metabolic requirements for glycine.

The name glycine is derived from the Greek word for "glue" because it occurs in large amounts in collagen, the structural protein that holds our connective tissue together. However, this small and simple amino acid does much more than provide structural integrity. It plays an essential role in numerous metabolic processes, serving as a building block for important biomolecules and neurotransmitters.

Where Does Glycine Naturally Occur?

Glycine is considered conditionally non-essential because, under normal circumstances, the body is capable of synthesizing significant amounts of this amino acid. However, there are situations in which glycine synthesis decreases or the body's demand increases, such as during pregnancy.

Calculations indicate that the body synthesizes approximately 3 g of glycine per day but requires around 15 g daily for the production of other biomolecules. Based on these figures, researchers assume that an additional 12 g of glycine from dietary sources may be necessary.

Glycine is the principal component of collagen, which forms the basic raw material for the production of gelatin. Since all multicellular animals contain collagen, meat and fish proteins contain approximately 4–5% glycine. Walnuts, pumpkin seeds, and soybeans are also excellent dietary sources, each containing more than 5% glycine. In silk fibroin, the structural protein of silk, glycine accounts for more than 40% of all amino acids.

What Is the Primary Function of Glycine in the Body?

In metabolism, glycine serves as a building block for components of genetic material, heme (the iron-containing pigment of red blood cells), creatine (the energy carrier of skeletal muscle), glutathione (the body's major endogenous antioxidant), and collagen.

Because of its exceptional tensile strength, collagen provides stability and structure to bones, tendons, ligaments, and skin. To produce collagen, the body links glycine alternately with the amino acids proline and hydroxyproline into peptide chains containing up to 3,000 amino acids, which are subsequently assembled into collagen fibers. Glycine is small enough to fit into the tight turns of these chains, making it essential for the dense packing of the structure and its remarkable tensile strength. Collagen accounts for more than 30% of all proteins in the human body.

In the brain and spinal cord, glycine functions as an inhibitory neurotransmitter, meaning that it suppresses the transmission of nerve signals. In doing so, glycine reduces the activity of specific muscle cells. The toxin produced by the bacterium causing tetanus blocks glycine-mediated neurotransmission and is therefore responsible for the life-threatening muscle spasms characteristic of tetanus.

Benefits

Building block for essential biomolecules and neurotransmitters
May improve sleep quality
Has been shown in studies to increase glutathione levels

What Are the Benefits of Glycine Supplementation?

Because the body's own synthesis of glycine may become impaired with advancing age or certain health conditions, and because dietary intake is not always sufficient, glycine has been extensively investigated as a dietary supplement. Although the body synthesizes approximately 3 g of glycine per day, it requires at least three times that amount solely for the daily production of collagen.

Since glycine is a major building block of collagen, it is frequently used as a supplement to support the health of joints, tendons, and bones, as well as in anti-aging products intended to promote younger-looking skin. Indeed, clinical studies have demonstrated that supplementation with 10 g of glycine increases serum glycine concentrations to levels consistent with the theoretical requirements for a threefold increase in collagen synthesis.

A glycine deficiency has been associated with reduced glutathione synthesis. Consequently, inadequate glycine availability may expose the body to increased oxidative stress and contribute to premature biological aging. Experimental studies have shown that glycine supplementation can increase glutathione levels.

Several clinical studies have demonstrated improvements in sleep quality and cognitive performance following glycine supplementation. These effects are believed to result from glycine's function as a neurotransmitter acting on specific receptors within the brain. Positive effects were observed with single doses of 3–5 g of glycine taken before bedtime.

Glycine is approved as a food additive within the European Union. No maximum intake level has been established because no adverse health effects have been identified to date. In clinical studies, doses of up to 0.8 g per kilogram of body weight (64 g for an individual weighing 80 kg) were well tolerated. Nevertheless, consuming large amounts of glycine through supplementation may cause gastrointestinal side effects such as abdominal pain and nausea. For supplementation, single doses of 3–5 g are therefore generally recommended.