Genetic Factors Affecting Glycine Levels and Health

This article is part of the PlexusDx Education Hub — your resource for evidence-based guidance on blood testing & biomarkers. Browse all Blood Testing & Biomarkers education

Glycine is the smallest amino acid, but it does outsized work. Your body uses it to build collagen, make glutathione, buffer stress in the nervous system, and support healthy metabolism. Blood glycine levels vary widely from person to person, and a meaningful share of that variation is written into your genes — in the enzymes that synthesize, recycle, and break glycine down.

Why glycine matters for health

Glycine is a building block for collagen (about one-third of collagen is glycine), a precursor to glutathione (the body’s master antioxidant), and a calming neurotransmitter that supports sleep and stable mood. Population studies have linked lower circulating glycine to a higher risk of type 2 diabetes and cardiometabolic strain, while higher glycine tends to track with better insulin sensitivity. Glycine sits at a metabolic crossroads, so its level is a useful window into several pathways at once.

GLDC and the glycine cleavage system

The gene that most directly governs how fast you break glycine down is GLDC, which encodes the main enzyme of the glycine cleavage system. Rare loss-of-function variants in GLDC cause nonketotic hyperglycinemia, a serious condition of glycine accumulation, but far more common regulatory variants nudge glycine turnover up or down within the normal range. GWAS work consistently identifies GLDC as a top determinant of blood glycine, alongside partner genes AMT and GCSH in the same enzyme complex.

SHMT1, CPS1, and glycine synthesis

SHMT1 (serine hydroxymethyltransferase) converts serine into glycine and connects glycine metabolism to the folate one-carbon cycle — the same cycle that MTHFR sits in. Variants here can shift how much glycine you generate and how one-carbon units flow toward methylation. CPS1 is another strong GWAS hit for circulating glycine, reflecting its role in nitrogen handling. Together these genes explain why two people eating similar diets can carry noticeably different glycine levels.

Glycine, methylation, and glutathione

Because SHMT1 links glycine to the folate cycle, glycine status and methylation are intertwined. Glycine is also a required ingredient, with cysteine and glutamate, for making glutathione. If glycine supply is limited, glutathione production can lag, which matters for oxidative stress and detoxification pathways. This is why glycine is best understood not in isolation but as one node in a network of interacting pathways your genetics helps calibrate.

Diet, lifestyle, and what you can influence

Genes set your baseline, but intake and habits move the needle. Glycine is abundant in collagen-rich foods, bone broth, gelatin, and the connective tissue of meat and fish. Protein quality, overall metabolic health, and physical activity all interact with your genetic tendencies. Genetic insight helps you understand why your levels sit where they do, so any dietary conversation with a provider or dietitian starts from your actual biology.

Where PlexusDx fits

The PlexusDx Precision Peptide Genetic Test analyzes 14 pathways, 49 peptides, 150+ genetic insights, including variants in amino-acid and one-carbon pathways relevant to glycine. It gives you pathway-level context — tendencies to discuss with a provider — not a diagnosis. PlexusDx tells you about your biology; it does not tell you what to put in your body. Results arrive through the secure Results Portal.

Frequently Asked Questions

Which genes affect glycine levels the most?

GLDC has the strongest effect, because it runs the glycine cleavage system that breaks glycine down. SHMT1 and CPS1 also rank among the top determinants in genome-wide studies. Variants in these genes shift how quickly you synthesize and clear glycine, which helps explain person-to-person differences in blood levels.

Are low glycine levels dangerous?

Not by themselves, but lower circulating glycine has been associated in population studies with higher type 2 diabetes and cardiometabolic risk. Glycine is one marker among many. Only a qualified healthcare provider can interpret your levels in the context of your full health picture and lab work.

Can I raise glycine through diet?

Often, yes. Glycine is concentrated in collagen-rich foods like bone broth, gelatin, and connective tissue, and adequate total protein supports synthesis. Your genetic tendencies in GLDC and SHMT1 influence your baseline, so responses vary. A dietitian or provider can tailor guidance to your goals and biology.

How does glycine connect to methylation?

Through SHMT1, which converts serine to glycine inside the folate one-carbon cycle — the same pathway MTHFR sits in. Glycine metabolism and methylation share machinery, so a variant affecting one can ripple into the other. This is why glycine is best viewed as part of an interconnected pathway network.

Curious where your glycine and methylation pathways stand? The Precision Peptide Genetic Test maps the named variants that shape amino-acid and one-carbon metabolism, giving you data to bring to a provider or dietitian.

The Precision Peptide Genetic Test analyzes how your genes influence peptide-related biological pathways. It does not recommend, prescribe, or determine which peptides you should use. Consult a qualified healthcare provider before beginning any peptide protocol.

This article is part of the PlexusDx Education Hub. Browse all Blood Testing & Biomarkers education