Everything You Need To Know About Glycine, The Amino Acid That Helps Us Sleep Better

Widely discussed in the context of nutrition and sleep, glycine is a multifunctional amino acid that may plump the skin and support muscle health. Found in some foods but also in supplement form, Vogue, with the help of two experts, decodes everything you need to know about the ingredient.

A good night’s sleep is the foundation of health and longevity, yet it’s something many of us take for granted. As we get older, stress, anxiety, hormonal changes, poor dietary habits, excessive screen time or alcohol can make those coveted seven to nine hours of restorative rest increasingly elusive.

In pursuit of a restful slumber, the sleep-deprived among us will try just about anything to catch 40 winks, from relaxation apps and high-tech gadgets to specialist bedding and supplements. Yet not with equal success. But there is one ingredient that is attracting attention among insomniac communities: glycine – but what is it, what does it do, and how can it improve sleep quality?

Named after the Greek word glykýs, meaning “sweet,” glycine is the smallest of the 20 amino acids used to build proteins – and yet it is biologically important as it is responsible for some critical functions. “Glycine is a building block of collagen, contributes to the production of glutathione and creatine, which plays an important role in muscle energy metabolism and acts as a neurotransmitter involved in the regulation of the nervous system,” Sam Gold, clinical nutritionist from The Skin Investment Clinic, explains. This is why it has become increasingly discussed in wellness, particularly in the spheres of sleep, sports and skin health. Yet, while our bodies can produce it naturally, it is often not in sufficient quantities.

What are the benefits of glycine?

Glycine is involved in many essential processes that support the skin, muscles and sleep.

Sleep: This is where the experts are most excited about the effects of glycine. “Glycine acts on neurotransmitter systems in the brain and may also influence the body’s natural drop in core temperature that occurs as we prepare for sleep,” Gold explains. She references a small study that showed “3g of glycine taken before bed may improve subjective sleep quality and reduce next-day fatigue following sleep restriction” but is quick to emphasise the word small as more research is necessary. She does advocate giving it a go if you’re “otherwise healthy and struggling with sleep quality.”

Muscles: Creatine is another widely discussed supplement, and glycine is involved in the body’s natural production of the compound as well as in protein synthesis. “Glycine has a plausible role here too,” Gold explains. “It is involved in creatine synthesis and is abundant in collagen and connective tissue, so there is a biological reason to think about it in relation to muscle and recovery, but again, biology isn’t the same as clinical evidence.” She again spotlights a review from 2024 that saw “promising findings around glycine, exercise recovery and muscle function,” but more trials are needed before dubbing it a “performance supplement.” Gold suggests, “If your goal is building or maintaining muscle, I’d put adequate protein, resistance training, sufficient energy, creatine where appropriate and good sleep considerably higher up the list.”

Skin: Collagen is known as the “scaffolding” or building block of the skin, and glycine is one of the main amino acids found in collagen, so it is important when it comes to skin structure. That being said, Kirsten Jackson, founder of The IBS Dietitian, wants to make clear that “being involved in collagen production doesn’t automatically mean that taking additional glycine will improve your skin. Most of the human research showing potential improvements in skin hydration or elasticity has looked at collagen peptides rather than isolated glycine supplements.” Just because it is crucial for collagen production doesn’t mean taking it will increase it.

Glycine occurs naturally in protein-rich foods, particularly those containing collagen and connective tissue. If you want to increase your intake through your diet, consider boosting the your intake of the following:

• Bone broth
• Beef and pork
• Chicken and turkey, especially with the skin and cartilage (chicken broth)
• Fish (with the skin on), especially salt cod
• Shellfish such as cuttlefish and octopus
• Gelatin
• Spirulina
• Soy
• Legumes such as beans, chickpeas, lentils, and mung beans
• Pumpkin seeds
• Walnuts and almonds

If you are struggling with sleep quality – which is different to not getting enough hours of sleep, Gold says that it is something to consider in line with “broader nutritional strategy where protein intake is inadequate or where there is a specific clinical reason to support connective tissue or antioxidant pathways.” But it is important to first check that the fundamentals are in place – avoiding caffeine later in the day, minimising scrolling, curbing alcohol consumption, sufficient diet or balancing hormonal symptoms – first. While generally well tolerated, both experts say to avoid these supplements if you’re pregnant or breastfeeding, while Gold adds that those with “significant kidney or liver disease, take multiple medications or have a complex medical condition to speak to their doctor or qualified healthcare professional before supplementing.”

Supplementing glycine gives the body an extra dose of the amino acid beyond that produced naturally in the body or found in food. They come in capsules, tablets, or powder form. When selecting a glycine supplement, the experts advise looking for pure glycine in the ingredient list with a “clearly stated dose and minimal unnecessary ingredients,” says Gold, who adds, “If you're a competitive athlete, look for independent certification such as Informed Sport to reduce the risk of inadvertent contamination with prohibited substances.” She recommends Thorne as it comes in a handy capsule. Jackson, however, prefers powders due to their practicality: “the amounts investigated for sleep are measured in grams rather than tiny milligram doses.” You can add to smoothies, protein shakes, yoghurt, soups, tea, herbal teas, coffee, or matcha to easily slip it into your routine.

• Sam Gold is a clinical nutritionist from The Skin Investment Clinic
• Kirsten Jackson, founder of The IBS Dietitian