Can I Take Glycine with Tresiba (Insulin Degludec)?

What Is Tresiba and Why Does Supplement Timing Matter?

Insulin degludec (Tresiba, Novo Nordisk) is an ultra-long-acting basal insulin approved by the FDA in September 2015 for adults and children aged 1 year and older with type 1 or type 2 diabetes. [1] Its half-life of approximately 25 hours and effective duration exceeding 42 hours create a flat, peakless action profile that differs meaningfully from older insulins such as insulin glargine (Lantus, ~24 hours) or detemir (Levemir, ~18 hours). [2]

That flat profile is clinically useful because it reduces overnight hypoglycemia. It also means any supplement that alters glucose disposal, insulin sensitivity, or glucagon release over a 6-to-10-hour nocturnal window will overlap with active insulin degludec concentrations. Glycine is one such supplement.

How Tresiba Works at the Molecular Level

After subcutaneous injection, insulin degludec forms soluble multi-hexamer chains that slowly dissociate into monomers for absorption. The result is a coefficient of variation for day-to-day glucose-lowering effect of roughly 20%, compared with 84% for NPH insulin in a crossover study reported by Heise et al. (2012). [3] This predictability is one reason clinicians prefer it for patients who are highly sensitive to glycemic variability.

Why Supplements Deserve a Closer Look

Many dietary supplements reach peak plasma concentration within 1 to 2 hours of ingestion. When taken at bedtime, that peak coincides with the overnight plateau of insulin degludec activity. Additive glucose-lowering effects during this window may not cause symptoms until 2 a.m. To 4 a.m., when counter-regulatory hormone responses are bluntest. For a patient whose fasting glucose target is already 80 to 130 mg/dL per American Diabetes Association standards, [4] even a 10 to 15 mg/dL reduction from a supplement can push values into hypoglycemic territory.

What Is Glycine and What Does It Do Metabolically?

Glycine is the simplest amino acid and the most abundant in human connective tissue. Adults synthesize roughly 3 g per day endogenously, but intake from food is typically 1.5 to 3 g/day, leaving a potential "gap" of several grams that some researchers argue is clinically relevant. [5]

Glycine as a Glucoregulatory Signal

Glycine acts on multiple glucose-regulatory systems simultaneously. The relevant mechanisms for insulin users are:

• GLP-1 secretion. Glycine receptors on intestinal L-cells stimulate glucagon-like peptide-1 (GLP-1) release, which augments glucose-dependent insulin secretion from beta cells. [6] This matters most in type 2 diabetes where residual beta-cell function exists, but even in type 1 disease it may modestly affect postprandial glucagon suppression.
• Glycogen synthesis. In rat hepatocyte models, glycine at physiological concentrations promoted hepatic glycogen deposition, effectively reducing hepatic glucose output. [7]
• Insulin sensitivity. A 2022 randomized controlled trial (N=60) by Ramirez-Villafaña et al. Published in Nutrients found that 15 g/day of glycine for 3 months reduced fasting glucose by 5.3 mg/dL and HOMA-IR by 0.4 units compared with placebo in patients with metabolic syndrome (P<0.05). [8] These are modest numbers, but they are directionally significant for someone on basal insulin.

Glycine and Glucagon Release

Glycine also stimulates glucagon secretion from pancreatic alpha cells, a counter-regulatory effect that theoretically buffers hypoglycemia. [9] This dual action on both insulin and glucagon is part of why glycine's net glycemic effect in humans is mild rather than dramatic. However, alpha-cell responsiveness is frequently impaired in long-standing type 1 diabetes, meaning that the glucagon-stimulating buffer may not function reliably in that population.

Glycine's Role in Sleep Quality

At bedtime doses of 3 g, glycine reduces core body temperature and improves subjective sleep quality, as shown in a small but replicated crossover trial by Inagawa et al. (N=11). [10] Deeper slow-wave sleep independently improves insulin sensitivity the following morning by reducing cortisol and growth hormone pulses that drive dawn-phenomenon hyperglycemia. This is a potentially favorable interaction for Tresiba users whose morning glucose consistently runs high. However, deeper sleep also means less arousal in response to early hypoglycemic symptoms, a risk factor that must be weighed for any patient with hypoglycemia unawareness.

Is the Glycine-Tresiba Interaction Pharmacokinetic or Pharmacodynamic?

The interaction is pharmacodynamic, not pharmacokinetic. Insulin degludec is degraded by non-specific proteolysis in peripheral tissues; it does not involve cytochrome P450 enzymes, UDP-glucuronosyltransferases, or major drug transporters. [2] Glycine is metabolized primarily by the glycine cleavage system in the liver and kidney mitochondria, a pathway entirely separate from insulin's degradation route.

No published data suggest glycine alters the absorption rate of subcutaneous insulin degludec, changes its protein binding (which is extensive, via albumin), or modifies its receptor affinity.

The concern is therefore about what happens downstream of both molecules. Both glycine and insulin degludec lower blood glucose by different but additive mechanisms. Their combined effect may exceed what either would produce alone.

What Does the Clinical Evidence Actually Show?

Glycine Studies in Diabetes Populations

The most rigorous human data come from studies using oral glycine supplementation in people with type 2 diabetes or prediabetes.

A 2009 study by Gannon and Nuttall (N=16 subjects with type 2 diabetes) found that a 5 g glycine dose taken with glucose blunted the glycemic excursion by approximately 50% compared with glucose alone, an effect the authors attributed primarily to augmented GLP-1 and insulin secretion. [6] This dose is similar to what many supplement products recommend.

A systematic review published in Frontiers in Bioscience (2016) identified 11 studies linking low plasma glycine levels to obesity, insulin resistance, and type 2 diabetes, noting that glycine supplementation consistently improved fasting glucose and lipid parameters in human trials, albeit with small effect sizes. [5]

No trial to date has enrolled patients specifically using insulin degludec or any basal insulin analog together with glycine. This is the central evidence gap.

Hypoglycemia Risk: What the Numbers Suggest

If glycine reduces fasting glucose by 5 to 10 mg/dL in people not on insulin, a patient already targeting 80 to 130 mg/dL on Tresiba starts the night with less margin before hypoglycemia (<70 mg/dL). The arithmetic alone justifies monitoring.

The DEVOTE trial (N=7,637), which compared insulin degludec to insulin glargine U100 in high-cardiovascular-risk type 2 patients, found that degludec produced significantly fewer severe nocturnal hypoglycemic episodes (hazard ratio 0.53, 95% CI 0.43 to 0.66, P<0.001). [11] That favorable nocturnal profile could be partially attenuated if a glucose-lowering supplement is added without dose adjustment.

The Sleep-Insulin Sensitivity Link

Consider a bedtime-glycine user on Tresiba: glycine improves slow-wave sleep, slow-wave sleep reduces cortisol by an estimated 15 to 20% overnight, and lower cortisol reduces hepatic glucose output. All three steps push morning glucose downward. This multi-step chain may explain why some patients anecdotally report lower morning readings after starting glycine, without any change to their Tresiba dose. The clinically appropriate response is not to simply accept the lower reading but to document it systematically and discuss it with a prescriber before attributing causality.

Pharmacodynamic Interaction Classification

The Natural Medicines database classifies the glycine-insulin interaction as a "minor" interaction based on additive glucose-lowering potential, with a recommendation to monitor blood glucose more frequently. [12] The Mayo Clinic Drug Interaction Checker does not flag a clinically significant interaction between glycine and any insulin formulation at typical supplement doses (3 to 5 g/day).

The American Diabetes Association 2024 Standards of Care state: "Patients using insulin should be counseled that any agent with glucose-lowering properties, including certain dietary supplements, may increase the risk of hypoglycemia and should prompt additional self-monitoring of blood glucose." [4] This general principle applies directly to glycine.

Who Is at Highest Risk for a Clinically Meaningful Interaction?

Type 1 Diabetes on Tresiba

People with type 1 diabetes have absent or negligible endogenous insulin secretion. Glycine's GLP-1-mediated stimulation of pancreatic insulin release is therefore irrelevant. However, glycine's direct effect on hepatic glucose output and insulin sensitivity remains. Coupled with impaired glucagon counter-regulation in long-standing type 1 disease, [9] this population warrants the most caution.

Tight HbA1c Targets

A patient maintaining HbA1c <7.0% (per ADA target) [4] already operates with narrow glucose margins. Adding any agent with even mild glucose-lowering properties compresses the buffer against hypoglycemia.

Nocturnal Hypoglycemia History

Any patient who has experienced nocturnal hypoglycemia on Tresiba, or who has hypoglycemia unawareness, should only add glycine under direct medical supervision with continuous glucose monitoring (CGM) in place for the first 2 to 4 weeks.

Patients on Concomitant GLP-1 Receptor Agonists

Patients using semaglutide (Ozempic, Wegovy) or liraglutide (Victoza) alongside Tresiba already have augmented GLP-1 activity. Adding glycine-mediated GLP-1 stimulation on top of that represents triple convergence on a single pathway, though the absolute incremental effect is likely small.

Glycine's Potential Benefits for Tresiba Users

The picture is not purely one of risk. Several effects of glycine may actually support better glycemic management in appropriate patients.

Collagen and Connective Tissue Support

Insulin-dependent patients with long disease duration face elevated risk of limited joint mobility and tendon stiffness partly linked to glycation of collagen. Glycine is the primary amino acid in collagen (33% by residue composition). Supplementation at 5 to 15 g/day is used in sports medicine and dermatology to support collagen synthesis. [13] This is a non-glycemic benefit with no interaction concern.

Oxidative Stress Reduction

A 2011 RCT (N=60) by Sekhar et al. Found that glycine supplementation (1.33 mmol/kg/day for 2 weeks) in elderly subjects significantly raised erythrocyte glutathione levels, a marker of antioxidant capacity. [14] Oxidative stress contributes to beta-cell dysfunction and vascular complications in diabetes. Improved glutathione synthesis is a plausible secondary benefit, though it is not a reason to start glycine without prescriber input.

Sleep and Dawn Phenomenon

As noted above, improved slow-wave sleep may reduce the dawn phenomenon in some patients. For Tresiba users whose fasting glucose consistently overshoots their target despite adequate basal dosing, bedtime glycine at 3 g is a low-risk intervention worth discussing with a clinician before trialing. The key is structured monitoring before concluding it is responsible for any change.

Practical Guidance: What to Do If You Are Already Taking Both

If you are currently taking glycine while on Tresiba and have not yet discussed this with your provider, follow these steps:

1. Do not stop either agent abruptly. Stopping Tresiba without a replacement plan risks diabetic ketoacidosis in type 1 patients.
2. Check fasting blood glucose every morning for 7 days and log the values.
3. Note any nocturnal symptoms. Sweating, waking at 2 to 4 a.m., palpitations, or morning headache may indicate nocturnal hypoglycemia.
4. Bring the log to your next appointment. Your prescriber may reduce your Tresiba dose by 10 to 20% if fasting values are consistently running 10 to 20 mg/dL below your target range, per standard clinical titration practice. [4]
5. Do not self-adjust Tresiba dose based on a supplement interaction without medical supervision.

Recommended Monitoring Protocol

| Timeframe | Action | |---|---| | Days 1 to 14 after adding glycine | Fasting glucose daily; pre-bed glucose if on tight targets | | Days 15 to 30 | Fasting glucose every other day if values are stable | | 3-month follow-up | HbA1c to confirm overall trend | | Ongoing | CGM preferred if history of nocturnal hypoglycemia |

Dose Considerations for Glycine

Most of the human metabolic evidence uses doses between 3 g and 15 g/day. Sleep studies use 3 g at bedtime as a single dose. Collagen-support protocols typically use 5 to 10 g/day taken with food or a collagen-containing protein supplement.

For Tresiba users, a starting dose of 3 g at bedtime is the most studied and lowest-risk entry point. Taking glycine with the evening meal rather than immediately before bed adds roughly 1 to 2 hours of digestion time before peak amino acid absorption, which shifts the glucose effect slightly earlier in the evening when patients are more likely to be awake and able to detect symptoms. This is a practical mitigation strategy, not a proven protocol.

Doses above 15 g/day have been used safely in short-term trials but are outside the range where glycemic interaction data exist for insulin-treated patients. No upper tolerable limit has been established by the National Institutes of Health for glycine, [15] but gastrointestinal discomfort (nausea, loose stools) is the most common adverse effect at doses above 10 g in a single sitting.

Summary of Interaction Classification

• Pharmacokinetic interaction: None identified.
• Pharmacodynamic interaction: Minor, additive glucose lowering via GLP-1 stimulation, hepatic glycogen promotion, and improved insulin sensitivity.
• Severity: Minor to moderate depending on individual glycemic targets and hypoglycemia history.
• Management: Frequent self-monitoring of blood glucose for 2 to 4 weeks; prescriber notification before initiating glycine at doses above 3 g/day.
• Contraindication: Glycine is not contraindicated with insulin degludec, but patients with hypoglycemia unawareness should use CGM if trialing the combination.