Glycine

Glycine is an amino acid with a number of important functions in the body. Glycine acts as a neurotransmitter, a component of collagen, and as a precursor to various biomolecules (e.g., creatine, heme), among other roles. Glycine is often considered conditionally essential, meaning it can usually be produced in the body in sufficient amounts. However, in certain contexts (e.g., pregnancy) more glycine may be needed from the diet. Glycine is found in most protein sources, meaning common sources of glycine include meat, eggs, soybeans, lentils, and dairy products.

A few studies have found supplementation with glycine can improve sleep quality, with subsequent benefits to cognitive function. High doses of glycine have been shown to improve symptoms of schizophrenia. Glycine may reduce the blood glucose response to carbohydrate ingestion.

Glycine is a major component of collagen (around 25% by weight) and for this reasons is often taken to improve joint health, but human evidence in this area is currently lacking.

In high amounts, glycine supplementation can cause gastrointestinal symptoms, including nausea and abdominal pain.

Glycine supplementation likely works through different mechanisms depending on the outcome of interest.

Glycine is a co-agonist of N-methyl-D-aspartate (NMDA) receptor, meaning glycine plays a role in activating this receptor in the brain. Glycine’s effect on the NMDA receptor has been proposed as underlying the improvements in both sleep and symptoms of schizophrenia with supplementation.

Glycine may benefit sleep by lowering core body temperature, as a warm body temperature can adversely affect sleep quality.