Evidence Level
Glycine is an underappreciated amino acid with diverse physiological roles. Its sleep benefits are well-documented: 3 g before bed lowers core body temperature and improves sleep quality without sedation or next-day grogginess (Yamadera et al., 2007). As a key component of collagen (comprising 33% of its structure), glycine supports skin, joint, and connective tissue health. When combined with NAC, it helps restore age-related declines in glutathione synthesis (Sekhar et al., 2011).
Recent studies highlight glycine's cardiovascular benefits. A 2019 meta-analysis of genome-wide studies involving 80,033 participants found that higher glycine levels are genetically associated with a lower risk of coronary heart disease, potentially mediated by blood pressure (Wittemans et al., 2019). Additionally, a 2022 systematic review/meta-analysis demonstrated that dietary intake of flaxseed, soy, and red clover—sources rich in glycine—improves lipid profiles by reducing total cholesterol (TC), low-density lipoprotein cholesterol (LDL-C), and increasing high-density lipoprotein cholesterol (HDL-C) (Błaszczuk et al., 2022).
In the context of periodontal health, a systematic review with meta-analysis of nine randomized controlled trials (n=462) found no significant difference in periodontal outcomes between erythritol, glycine, and trehalose as air-polishing powders. However, erythritol was ranked highest for reducing probing pocket depth (PPD) (Zi-le et al., 2025). Furthermore, a 2015 meta-analysis of 9,626 broilers across ten studies demonstrated that dietary glycine significantly influences feed conversion efficiency and growth rate in poultry, with optimal effects dependent on methionine:threonine:selenocysteine ratios and cysteine levels (Siegert et al., 2015).
Overall, glycine is a versatile amino acid with benefits spanning sleep quality, collagen synthesis, cardiovascular health, and animal husbandry. Its safety profile is excellent, as it is sweet-tasting and well-tolerated even at high doses.