Understanding Glycine Deficiency
Glycine is the simplest amino acid in the human body and is classified as non-essential because the body can synthesise it from serine and other precursors. However, "non-essential" does not mean unimportant. Research has increasingly supported the concept of glycine being "conditionally essential" — meaning endogenous synthesis may not meet the full demand in certain populations or physiological states (Razak et al., 2017).
Glycine is a key building block of collagen (the most abundant protein in the body), a neurotransmitter in the brainstem and spinal cord, a co-substrate for glutathione synthesis, and a regulator of sleep through glycine receptors in the suprachiasmatic nucleus.
A true clinical glycine deficiency syndrome is not recognised in standard medicine. But functional insufficiency — where glycine supply falls below the body's utilisation needs — is a plausible and increasingly discussed concept, particularly in high-protein dieters, athletes, elderly individuals, and those with poor dietary collagen intake.
Symptoms That May Indicate You Could Benefit
Poor Sleep Quality
Glycine influences sleep architecture. A randomised crossover study in subjects with self-reported sleep dissatisfaction found that glycine supplementation improved subjective sleep quality and reduced daytime sleepiness compared to placebo (Bannai et al., 2012). The proposed mechanism involves lowering core body temperature at sleep onset and modulating activity in the sleep centres of the brain.
Slow Muscle Recovery and Training Fatigue
Collagen synthesis requires glycine. After heavy resistance training, connective tissue repair — tendons, ligaments, and the extracellular matrix of muscle — draws on the glycine pool. People with high training loads and low dietary collagen intake (those who eat mainly lean muscle meat and avoid bone broth, skin-on fish, and cartilaginous cuts) may have a relative shortfall.
Joint Discomfort
Glycine is the most abundant amino acid in collagen, which is the primary structural protein of cartilage, tendons, and ligaments. While glycine supplementation is not a treatment for joint disease, interest in glycine as a component of joint-support regimens has grown, particularly among older athletes.
Gut Barrier Function
Glycine supports intestinal epithelial integrity and has anti-inflammatory effects in the gut. People with digestive complaints or inflammatory gut conditions may have higher glycine utilisation.
At-Risk Groups
- High-volume athletes: Increased connective tissue turnover demands more glycine.
- Older adults (50+): Reduced collagen synthesis rates and lower dietary intake of collagen-rich foods increase the gap between supply and demand.
- Vegetarians and vegans: Animal connective tissue (skin, bones, cartilage) is the richest dietary source of glycine. Plant-based diets are lower in glycine-dense foods.
- Low-collagen diets: People who eat only lean meat (without skin or bones) and no bone broth effectively consume far less dietary glycine than traditional diets.
- People with chronic stress: Glycine is consumed in glutathione synthesis, which is upregulated under oxidative stress.
How It Is Tested
Plasma amino acid panels can measure glycine concentrations, but clinical reference ranges for "optimal" glycine are not established in the same way as for essential nutrients. Assessment is largely symptomatic.
Nordic and Estonian Context
Traditional Estonian cuisine historically included bone broths, pig ear dishes, and skin-on preparations that naturally supplied dietary glycine. Modern leaner eating patterns, with boneless skinless chicken breast and protein powder as the main protein sources, have reduced dietary glycine intake compared to historical norms. Athletes in Estonia who follow high-protein, low-fat, whole-food diets based on lean protein may be among those with the lowest dietary glycine.
When to Supplement vs Diet
Food-first strategies for glycine include bone broth (the richest single dietary source), collagen protein powder, skin-on fish, and cuts of meat with connective tissue. However, hitting the amounts used in sleep research may require supplementation.
Products available at maxfit.ee include MST L-Glycine vegan 1000mg 120caps, MST L-Glycine vegan 1000mg 60caps, and OstroVit Glycine 200g Naturaalne. Visit the glycine category at maxfit.ee.
References
Bannai, M., Kawai, N., Ono, K., Nakahara, K., & Murakami, N. (2012). The effects of glycine on subjective daytime performance in partially sleep-restricted healthy volunteers. Frontiers in Neurology, 3, 61. https://pubmed.ncbi.nlm.nih.gov/22529837/
Razak, M. A., Begum, P. S., Viswanath, B., & Rajagopal, S. (2017). Multifarious beneficial effect of nonessential amino acid, glycine: a review. Oxidative Medicine and Cellular Longevity, 2017, 1716701. https://pubmed.ncbi.nlm.nih.gov/28337245/
Shaw, G., Lee-Barthel, A., Ross, M. L., Wang, B., & Baar, K. (2017). Vitamin C-enriched gelatin supplementation before intermittent activity augments collagen synthesis. American Journal of Clinical Nutrition, 105(1), 136-143. https://pubmed.ncbi.nlm.nih.gov/27852613/
FAQ
Is glycine an essential amino acid?
Glycine is classified as non-essential because the body synthesises it. However, synthesis rates may not always meet demand — particularly in athletes, older adults, or vegans — making it conditionally essential in some contexts.
How much glycine should I take for sleep?
The randomised trial supporting sleep improvement used a dose that aligns with what is found in typical supplements. Check the product label for the specific amount per serving of whatever glycine supplement you choose.
Can I get enough glycine from food?
For most people eating traditional diets that include bone broth, skin-on meat, and gelatinous cuts, dietary glycine intake may be adequate. Those on lean-protein or plant-based diets are more likely to benefit from supplementation.
