What Are the Symptoms of Glycine Deficiency?

November 18, 2025 •

4 min read

While the body can produce glycine, it often cannot produce enough to meet metabolic demands, making it a conditionally essential amino acid and a potential source of deficiency. Understanding what are the symptoms of glycine deficiency is crucial for overall health, as low levels can impact everything from sleep quality to cognitive function.

Quick Summary

Low glycine levels can cause persistent fatigue, muscle weakness, and cognitive impairment often described as brain fog. Poor sleep, digestive problems, and issues with skin and wound healing are also potential indicators.

Key Points

Fatigue and Weakness: Unexplained chronic fatigue, low energy, and muscle weakness are key indicators, potentially stemming from reduced creatine synthesis and energy metabolism.
Sleep Problems: Difficulty falling asleep, staying asleep, or feeling unrested upon waking can signal a deficiency, as glycine helps calm the nervous system and regulate sleep.
Cognitive Issues: Brain fog, poor concentration, and memory lapses may result from glycine's diminished function as a neurotransmitter in the brain.
Skin and Healing: Slow wound healing, sagging skin, and brittle hair or nails can occur due to inadequate collagen and keratin production, both of which require glycine.
Digestive Discomfort: A compromised gut lining and issues like bloating and indigestion can be linked to low glycine, which is important for gut health.
Anxiety: As an inhibitory neurotransmitter, low glycine can contribute to increased anxiety and nervousness due to heightened nerve excitability.

The Crucial Role of Glycine

Glycine is the smallest and simplest of all amino acids, yet it plays a monumental role in human health. Beyond its structural function as a building block for proteins, glycine is essential for synthesizing crucial compounds like collagen, creatine, and glutathione. It also functions as an inhibitory neurotransmitter in the central nervous system, helping to regulate nerve impulses, which is key for mood and sleep. Given its wide-ranging responsibilities, a shortage of glycine can lead to a cascade of observable symptoms throughout the body.

Neurological and Cognitive Symptoms

Poor Sleep Quality

One of the most well-documented effects of low glycine levels is its impact on sleep. As a neurotransmitter, glycine helps to calm the nervous system and promote restful sleep. It does this by lowering the core body temperature and facilitating vasodilation (blood vessel widening), which signals the body to wind down. A deficiency can lead to several sleep issues, including difficulty falling or staying asleep, and can leave a person feeling unrefreshed despite getting a full night's rest.

Brain Fog and Mental Fatigue

Glycine plays a significant role in cognitive function and nerve cell communication. When levels are insufficient, many individuals report experiencing a state of 'brain fog'. This can manifest as difficulty concentrating, memory lapses, or a general sense of mental sluggishness. Tasks that require mental effort may feel more challenging than usual, and mental clarity can be significantly diminished.

Anxiety and Mood Regulation

Glycine's inhibitory action on the central nervous system means it can also help regulate mood and reduce anxiety. It binds to NMDA receptors, preventing them from becoming overstimulated, which is often linked to increased anxiety levels. When glycine is low, this calming effect is compromised, potentially leading to increased feelings of anxiety and irritability.

Physical and Muscular Symptoms

Chronic Fatigue and Weakness

Glycine is needed to convert glucose into energy and to synthesize creatine, a compound that provides energy to muscles. A deficiency can manifest as a general feeling of weakness and chronic fatigue, making daily physical tasks feel more strenuous. This is different from sleepiness related to poor sleep quality, though the two can be intertwined. The fatigue is rooted in the body's decreased ability to produce and utilize energy effectively.

Slow Wound Healing

As a primary component of collagen, glycine is vital for the repair and regeneration of skin and other tissues. In a state of deficiency, collagen synthesis is compromised, which can significantly slow down wound healing. Minor cuts, bruises, or injuries may take noticeably longer to recover from than they would otherwise. This slower recovery is often one of the more subtle but telling symptoms of low glycine.

Hair and Nail Problems

Both hair and nails rely on keratin, a structural protein that also depends on glycine for its strength and integrity. A lack of sufficient glycine can weaken the keratin structure, potentially leading to brittle hair and nails that are prone to breakage.

Digestive Issues

Glycine supports the production of stomach acid and helps maintain the integrity of the gut lining. An insufficient supply can lead to digestive discomfort, including bloating and indigestion. Some research even links low glycine to increased gut permeability, commonly known as 'leaky gut syndrome'.

Symptoms and Mechanisms: A Comparison


Symptom	Associated Glycine Function	Result of Deficiency
Chronic Fatigue	Energy conversion, Creatine synthesis	Reduced energy production, feeling of weakness
Poor Sleep	Calming neurotransmitter, Body temperature regulation	Difficulty falling/staying asleep, daytime fatigue
Brain Fog	Nerve cell communication, Neurotransmitter balance	Difficulty concentrating, mental sluggishness
Anxiety	Inhibitory neurotransmitter	Increased nerve excitability, heightened anxiety
Slow Wound Healing	Collagen synthesis (approx. 33% glycine)	Compromised tissue repair and skin elasticity
Skin Problems	Collagen and Keratin formation	Sagging skin, dull complexion, premature aging
Digestive Issues	Gut lining maintenance, Stomach acid production	Bloating, indigestion, increased gut permeability

Who is at Risk for Glycine Deficiency?

While severe, inherited deficiencies are rare, subclinical or conditional deficiencies can occur in certain populations. Individuals with low-protein diets, such as vegans, may be at a higher risk. Those with certain metabolic conditions, liver disease, or inflammatory conditions may also experience altered glycine metabolism. Additionally, athletes and those in recovery from injury may have increased glycine needs.

How to Address Potential Glycine Shortages

If you suspect you have a glycine deficiency based on the symptoms above, the first step is to consult a healthcare professional. They can properly diagnose the issue and rule out other underlying health conditions.

For dietary support, consuming foods rich in glycine can be beneficial. These include:

Meat: Particularly cuts with connective tissue like beef, pork, and chicken
Bone Broth: An excellent source of collagen and, by extension, glycine
Fish: Good sources include salmon and trout
Legumes: Soybeans, lentils, and beans contain moderate amounts
Dairy: Cheese and milk contain smaller amounts
Seeds: Pumpkin and sunflower seeds

Dietary supplementation is another option and can be particularly useful for those who can't meet their needs through diet alone. Glycine is available in powder or capsule form and has been used in studies for its sleep and cognitive benefits. Supplementation can also support collagen production for skin and joint health.

Conclusion

Glycine deficiency can affect multiple body systems, leading to a range of symptoms from chronic fatigue and cognitive difficulties to poor sleep and skin problems. While glycine is a non-essential amino acid, many people's endogenous production is insufficient. Recognizing the signs and addressing potential low levels through diet or supplementation, under medical guidance, is an important step towards improving overall health. For more detailed medical information, the National Institutes of Health (NIH) is a valuable resource on amino acid functions and metabolism.

Frequently Asked Questions

Yes, as an inhibitory neurotransmitter, glycine helps calm the central nervous system. Low levels can lead to overstimulation of NMDA receptors, which is linked to increased anxiety and can negatively impact mood regulation.

Fatigue from a glycine deficiency is often accompanied by poor sleep and mental fogginess. However, many conditions cause fatigue, so it's important to consult a doctor for a proper diagnosis rather than self-diagnosing.

Foods rich in glycine often contain high levels of collagen. Excellent sources include meat (especially cuts with connective tissue), bone broth, and fish. Some plant-based sources include legumes like lentils and soybeans.

Severe, inherited glycine deficiencies are very rare. However, subclinical or conditional deficiencies can occur, especially in individuals with low-protein diets or certain metabolic conditions, as the body's endogenous production may not be enough.

Some studies suggest that glycine supplementation can improve sleep quality and lessen daytime fatigue. It may help regulate sleep by lowering core body temperature.

Adequate glycine is essential for collagen synthesis, which is crucial for skin elasticity and firmness. Increasing glycine intake may help improve skin health, elasticity, and hydration, leading to a more youthful appearance.

While supplementation is an option, it is best to speak with a healthcare provider first. They can determine if supplementation is appropriate for you, especially if you take other medications or are pregnant or nursing.