Glycine

Glycine is the smallest and one of the most useful amino acids your body makes. It’s the amino acid your body reaches for to build collagen, to manufacture its master antioxidant glutathione, and to quietly calm the nervous system at night. It’s non-essential — meaning you can synthesize it — but a growing line of research asks whether “can make it” and “makes enough of it” are really the same thing.

What is glycine?

Glycine is a non-essential proteinogenic amino acid, the simplest of the twenty that build our proteins. Its side chain is a single hydrogen atom, which makes it small and flexible enough to fit into tight molecular corners other amino acids can’t — which is exactly why collagen, the body’s most abundant protein, is packed with it. You’ll see it written as Gly or the single letter G. It has a mildly sweet taste, which is where its name comes from.

What does glycine do in the body?

Glycine punches far above its size. It is a structural building block of collagen, where roughly one amino acid in three is glycine — so it underpins skin, tendon, cartilage and bone. It’s also a precursor the body uses to make glutathione (its master antioxidant), creatine, heme (part of red blood cells), and bile salts. And in the spinal cord and brainstem it acts as an inhibitory neurotransmitter, a calming counterweight to the excitatory signals that keep you wired.

Where do you get glycine?

The richest food sources are the collagen-heavy parts of animals: bone broth, gelatin, and the skin, connective tissue and bones of meat, poultry and fish. Dairy, eggs and legumes contribute too. Because a modern diet often skips the collagen-rich “nose-to-tail” cuts our ancestors ate, some researchers think typical intakes sit below what’s ideal — the everyday reason people reach for a glycine or collagen supplement.

What does the research show?

The most concrete human evidence is for sleep. In small controlled trials, about 3 grams of glycine before bed improved people’s subjective sleep quality and next-day alertness and helped them fall asleep faster — a real, low-risk signal, even if the studies are small. Its role as a collagen backbone and a glutathione precursor makes glycine a biologically sensible target for skin, joint and metabolic health, and observational human work links better glycine status to healthier metabolic markers. That second bucket is promising but mixed and mostly associational — the raw material clearly matters; the proof that extra glycine visibly moves those outcomes in people is still arriving.

Is glycine safe?

Glycine has a reassuring safety record. It’s been used in gram-scale doses in human trials with only mild, temporary effects — occasionally soft stools or a little nausea at high intakes. As with any supplement, the sensible move is to start at the low end and see how you respond.