The Complex Relationship Between Glycine and Cancer

Glycine, the smallest and simplest amino acid in the human body, occupies a paradoxical place in cancer biology. Fast-growing cancer cells gobble it up to fuel their replication, yet circulating glycine in the bloodstream has been linked to reduced risk of certain cancers, and glycine supplements have shown anti-tumor effects in animal models. The relationship resists a clean narrative because glycine sits at a metabolic crossroads, feeding into pathways that build new cells, maintain antioxidant defenses, produce collagen, and regulate blood vessel growth. Whether glycine acts as friend or foe depends heavily on context: the type of cancer, where the glycine is, and what the surrounding cells are doing with it.

Why Cancer Cells Crave Glycine

Rapidly dividing cells need raw materials, and glycine is one of the most versatile building blocks available. It contributes directly to the construction of proteins, DNA, and RNA. It feeds into a metabolic network called one-carbon metabolism, which shuffles single carbon atoms through a series of chemical reactions that ultimately produce the nucleotides (the letters of the genetic code) a dividing cell needs to copy its genome. Serine and glycine are tightly linked in this process, and together they supply precursors for proteins, nucleic acids, and lipids that are crucial to cancer cell growth.

1PubMed Central. Serine and glycine metabolism in cancer

A landmark metabolic profiling study examined how dozens of metabolites were consumed and released across the NCI-60 panel of cancer cell lines and found that glycine consumption was strongly correlated with how fast the cells were dividing. The fastest-growing cancer cells didn’t just passively absorb glycine; they actively ramped up their own internal glycine-production machinery. When the researchers interfered with glycine uptake or its synthesis inside mitochondria, the rapidly proliferating cells were hit hardest.

2PubMed Central. Metabolite profiling identifies a key role for glycine in rapid cancer cell proliferation

A key enzyme in this process is SHMT2 (mitochondrial serine hydroxymethyltransferase), which converts serine into glycine inside the mitochondria and generates a one-carbon unit in the process. Many human tumors, including liver cancer, breast cancer, and non-small cell lung cancer, show elevated levels of SHMT2 expression. The enzyme essentially feeds two needs at once: it produces glycine and supplies the one-carbon units required for building DNA bases.

3PubMed Central. Roles of Mitochondrial Serine Hydroxymethyltransferase 2 (SHMT2) in Human Carcinogenesis

How Glycine Gets Inside Tumor Cells

Cancer cells don’t rely solely on making their own glycine. They also import it from outside. One of the transporters responsible for shuttling glycine across the cell membrane is GLYT1, a specific glycine transporter. When researchers knocked down GLYT1 in rapidly dividing lung and colon cancer cell lines, the number of viable cells dropped by roughly 30%, and the replication rate fell by about half. Using a chemical inhibitor of GLYT1 extended the doubling time of fast-growing cells by about eight hours and significantly reduced the number of viable cells after four days of treatment.

4PubMed Central. Reduction of Rapid Proliferating Tumour Cell Lines by Inhibition of the Specific Glycine Transporter GLYT1

This finding matters because it suggests a potential therapeutic angle. If you can cut off the external glycine supply to a tumor, especially one that is already struggling to make enough internally, the cells slow down. One conference abstract demonstrated this principle by showing that when a mitochondrial enzyme involved in glycine production (MTHFD2) was knocked out in breast cancer cells, those cells became dependent on external glycine. Blocking glycine uptake in that context further suppressed their growth.

5Cancer Research. Abstract 1803: Lethal synthesis: Potent anticancer activity of a glycine uptake inhibitor in tumor cells with mitochondrial methylenetetrahydrofolate dehydrogenase (MTHFD2) knocked down

Glycine Decarboxylase and Tumor-Initiating Cells

Beyond merely fueling rapid division, glycine metabolism appears to play a role in the earliest stages of cancer formation. Research published in Cell identified glycine decarboxylase (GLDC), the enzyme that breaks down glycine, as critical for tumor-initiating cells in non-small cell lung cancer. These tumor-initiating cells expressed high levels of both GLDC and an oncogenic stem cell factor called LIN28B, and both were required for tumor growth. When GLDC was overexpressed in normal cells, it promoted cellular transformation, essentially pushing them toward becoming cancerous. Critically, a catalytically inactive version of the enzyme didn’t have the same effect, confirming that the enzymatic activity itself, not just the protein’s presence, was what mattered.

6PubMed. Glycine decarboxylase activity drives non-small cell lung cancer tumor-initiating cells and tumorigenesis

This connects back to the broader metabolic picture. Excessive activation of glycine and serine biosynthesis can drive tumor formation by providing single carbon units for one-carbon metabolism, which in turn supplies the proteins, nucleic acids, and lipids tumors need to grow.

7PubMed Central. Serine, glycine and one‑carbon metabolism in cancer

The Anti-Angiogenic Side of Glycine

Here is where the story flips. While glycine metabolism inside cancer cells fuels their growth, glycine acting on blood vessel cells from the outside appears to do the opposite. Tumors need to recruit new blood vessels (a process called angiogenesis) to grow beyond a tiny size. Research has found that glycine can block this process by activating a chloride channel on endothelial cells, the cells that line blood vessels.

In endothelial cells, researchers identified a receptor nearly identical to the glycine-gated chloride channel found in spinal cord neurons. When glycine binds to this receptor, it opens a chloride channel, which changes the cell’s electrical charge in a way that blocks calcium from entering. Since calcium influx is needed for growth factor signaling, this effectively shuts down the signals that would tell the endothelial cell to divide and migrate toward the tumor. Glycine increased chloride influx into endothelial cells roughly tenfold and significantly diminished their proliferation and migration in response to growth signals. The effect was reversed by strychnine, a known blocker of glycine receptors, confirming that the mechanism runs through the glycine receptor.

8PubMed. Glycine as a potent anti-angiogenic nutrient for tumor growth

This anti-angiogenic effect has been tested in a colorectal cancer model in rats. Animals fed a diet containing 5% glycine for two weeks showed reduced tumor growth and lower blood vessel density within their tumors. VEGF (a key growth signal for blood vessels) and conditioned media from tumor cells increased endothelial cell proliferation, migration, and tube formation by up to 267%, but glycine completely neutralized that effect. Strychnine, again, blocked glycine’s protective action.

9PubMed. Glycine inhibits angiogenesis in colorectal cancer: role of endothelial cells

So glycine inside a cancer cell helps it replicate, but glycine acting on the blood vessels trying to feed the tumor can starve it. The same molecule, doing different things in different cellular neighborhoods.

Blood Glycine Levels and Pancreatic Cancer Risk

Epidemiological studies add another layer. Two prospective cohort studies have found that people with higher circulating glycine levels tend to have a lower risk of pancreatic cancer. In one study, people in the highest quartile of blood glycine had about 75% lower odds of developing pancreatic cancer compared to those in the lowest quartile.

10PubMed Central. The Association between Serum Serine and Glycine and Related-Metabolites with Pancreatic Cancer in a Prospective Cohort Study

A separate, larger study using the UK Biobank found a similar pattern. After correcting for multiple comparisons, plasma glycine was the only amino acid with a significant inverse association with pancreatic cancer risk. People with high glycine levels had about a 21% lower risk of developing the disease compared to those with low levels.

11PubMed. Elevated circulating glycine levels are associated with reduced pancreatic cancer risk: A prospective cohort study based on the UK biobank

These results don’t mean that taking glycine supplements prevents pancreatic cancer. Blood levels of glycine reflect a web of metabolic processes, including liver function, diet, and how actively other tissues are consuming glycine. A tumor that is aggressively pulling glycine out of the bloodstream could itself lower circulating levels. The association could be partly a signal that something metabolically problematic is already underway in people with low glycine, rather than evidence that high glycine is directly protective. Still, the consistency across studies is worth noting, particularly because it contrasts with the intracellular story where glycine feeds tumor growth.

Glycine in the Tumor Microenvironment

Cancer doesn’t happen in isolation. Tumors reshape the tissue around them, recruiting normal cells to do their bidding. One recently described mechanism involves glycine’s role as the most abundant amino acid in collagen, the structural protein that forms the scaffold of connective tissue. In colorectal cancer, tumor cells secrete a signaling molecule called TGF-β1, which triggers nearby fibroblasts (the cells that produce collagen) to ramp up their glycine production. These cancer-associated fibroblasts activate a glycine-synthesis pathway and use the glycine to manufacture large amounts of collagen, which in turn stiffens the tissue around the tumor in ways that can promote cancer progression. When researchers blocked the rate-limiting enzyme in this glycine synthesis pathway, collagen production in the fibroblasts dropped.

12MedComm – Oncology. Colorectal Cancer Cells Promote de novo Glycine Synthesis for Collagen Production in Cancer‐Associated Fibroblasts by Secreting TGF‐β1

On the immune side, glycine may also influence how immune cells behave in the tumor’s vicinity. Research on triple-negative breast cancer found that combining glycine with β-elemene (a compound derived from a traditional medicinal herb) suppressed the polarization of macrophages into a tumor-promoting form. The combination worked by dampening a signaling pathway (IL-6/JAK2/STAT3) that tumors often exploit to create an immunosuppressive environment.

13PubMed Central. Suppressing M2 Macrophage Polarization by Glycine Combined with β-Elemene via the IL-6/JAK2/STAT3 Signaling Pathway to Inhibit Triple-Negative Breast Cancer Progression

Dietary Restriction of Serine and Glycine

If cancer cells are hungry for glycine, one intuitive strategy is to starve them. In mouse models, restricting dietary serine and glycine has shown measurable effects. Mice fed diets lacking these two amino acids accumulated unusual lipid species called deoxysphingolipids and showed reduced tumor growth in xenograft models (tumors grown from transplanted human cancer cells).

14PubMed Central. Serine restriction alters sphingolipid diversity to constrain tumour growth

The serine/glycine-free diet approach has attracted research interest because it targets a metabolic vulnerability without requiring a drug. But there are significant caveats. Humans cannot easily eliminate serine and glycine from their diets since both are found in most protein-containing foods and are also made internally by the body. The mouse studies use carefully controlled synthetic diets that would be nearly impossible to replicate in free-living people. And some tumors can compensate by ramping up their own internal production of these amino acids, making dietary restriction alone insufficient. The NRF2 pathway, for instance, has been shown to drive serine and glycine biosynthesis in lung cancer cells, providing substrates for the tumor’s antioxidant defenses and nucleotide production even when external supply is limited.

15Cancer Discovery. NRF2 Drives Serine/Glycine Biosynthesis to Promote NSCLC Tumorigenesis

Protecting Against Chemotherapy Side Effects

While the debate over glycine’s pro- or anti-tumor role continues, one area where glycine supplementation looks more straightforwardly beneficial is in protecting healthy tissue from the collateral damage of chemotherapy. Chemotherapy drugs are notoriously hard on the liver, and animal research has found that dietary glycine can substantially reduce that damage. In rats receiving common chemotherapy regimens (FOLFIRI and FOLFOX, widely used for colorectal cancer), glycine supplementation cut liver enzyme levels, a marker of liver damage, to 25-50% of control values. A type of fatty liver damage called microvesicular steatosis was also significantly reduced. The mechanism appeared to involve calming the liver’s resident immune cells (Kupffer cells) and improving blood flow through the liver’s tiny vessels.

16PubMed. Dietary glycine protects from chemotherapy-induced hepatotoxicity

Cancer cachexia, the severe muscle wasting that affects many cancer patients, represents another area where glycine may help without directly engaging the tumor. In a mouse model of cancer cachexia, glycine supplementation attenuated the loss of fat and muscle mass, reduced markers of inflammation and muscle breakdown, and showed trends toward preserving body weight and muscle function. The effect appeared to work through dampening inflammatory signaling and oxidative stress rather than through any direct anti-tumor mechanism.

17Clinical Nutrition. Glycine administration attenuates skeletal muscle wasting in a mouse model of cancer cachexia

Drugs That Target Glycine Metabolism

The most active area of translational research involves developing drugs that block glycine-related enzymes inside cancer cells. Several research groups have focused on SHMT1 and SHMT2 inhibitors, since these enzymes sit at the junction between serine, glycine, and one-carbon metabolism. A compound called SHIN1 has shown promise in gastric cancer cells, where it raised serine levels (because serine was no longer being converted to glycine) and lowered glycine levels. When combined with the standard chemotherapy drug 5-fluorouracil, SHIN1 enhanced the anti-cancer effect.

18npj Precision Oncology. SHMT inhibitor synergizes with 5-Fu to suppress gastric cancer via cell cycle arrest and chemoresistance alleviation

Other researchers have developed sub-micromolar SHMT1/2 inhibitors and confirmed their mechanism through crystallography and metabolic analysis. These compounds blocked the production of glycine from glucose and serine in cancer cells, and their anti-cancer activity could be rescued by adding glycine and formate back to the growth medium, confirming that the drugs were working by cutting off the glycine supply. Combinations with existing antifolate drugs (a class that includes methotrexate) showed synergistic effects.

19Cancer Research. Small molecule inhibitors of SHMT1/2 validate serine metabolism as a target in the treatment of c-Myc positive solid tumors

The GLDC research described earlier also pointed toward combination strategies. Low doses of methotrexate specifically blocked the proliferation advantage that GLDC overexpression provided. When methotrexate was combined with GLDC knockdown in lung cancer cells, the result was far more effective than either approach alone, suggesting that shutting down both glycine breakdown and one-carbon metabolism simultaneously could be a potent strategy.

20Cell. Glycine Decarboxylase Activity Drives Non-Small Cell Lung Cancer Tumor-Initiating Cells and Tumorigenesis

Detoxification and the GLYAT Connection

Glycine also plays a housekeeping role that may be relevant to cancer prevention. The enzyme glycine N-acyltransferase (GLYAT) uses glycine to conjugate and neutralize certain toxic compounds in the liver, a process known as phase II detoxification. Interestingly, GLYAT expression is downregulated in liver and breast cancer cells. Whether this is a cause or consequence of the cancer is unclear, but the loss of GLYAT activity could theoretically impair the body’s ability to clear certain carcinogenic metabolites, while also freeing up glycine for other uses by the tumor.

Tracking glycine into purine nucleotides directly in human tissue has also been done. Using isotope-labeled glucose, glycine, and serine in freshly resected lung cancer tissue from patients, researchers showed that cancer tissue actively synthesized purines from these precursors. Serine was preferentially funneled into purine rings over glycine in both tissues and cell lines. In some cell lines, suppressing the oncogene MYC reduced this incorporation and slowed proliferation, though not universally, highlighting that the metabolic wiring varies from tumor to tumor.

21PubMed Central. De novo synthesis of serine and glycine fuels purine nucleotide biosynthesis in human lung cancer tissues

What This Means for People Taking Glycine Supplements

Glycine supplements are widely available and marketed for sleep, joint health, and general wellness. If you are a cancer patient or someone with a family history, the research above can feel alarming: should you avoid glycine? The honest answer is that the evidence does not support either panic or enthusiasm. The intracellular demand for glycine in fast-growing tumors is largely met by the cell’s own synthesis machinery and by serine-to-glycine conversion, not by oral supplementation. Dietary glycine passes through the gut, enters the bloodstream, and gets distributed across every tissue in the body. There is no evidence that the modest rise in blood glycine from a typical supplement dose selectively feeds a tumor.

On the other hand, the anti-angiogenic effects, the chemoprotective liver data, and the cachexia findings are all from animal models and have not been tested in rigorous human cancer trials. No clinical guidelines currently recommend glycine supplementation as a cancer therapy or a cancer prevention strategy. If you are undergoing treatment, any supplement decision should involve your oncologist, not because glycine is known to be dangerous, but because the interactions with specific chemotherapy regimens have not been mapped out in people. The science here is genuinely unsettled, and anyone claiming otherwise is outrunning the data.