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You’re entitled to a good night’s sleep. Getting your “beauty sleep” isn’t vain if the alternative is puffy eyes, brain fog, and a lack of motivation. In order to relieve yourself of that under-eye baggage, you may need some assistance. Introducing glycine: an amino acid and neurotransmitter that could help you achieve a fairytale-like ending to your day.

Once upon a time—in 1820 to be precise—European chemist Henri Braconnot discovered glycine through the acid hydrolysis of gelatin.Wang2013 He boiled gelatin with sulfuric acid to break the gel down into its simpler components. The discovery was sweet, not just because of glycine’s potential, but also because of its properties.

Glycine, also known as glycocoll, is a crystalline solid as sweet as glucose, thus both names share the Greek word meaning “sweet”: glykys.Wang2013 Take a look at the ingredients in your favorite sweetener. Is glycine present?

Glycine as an Amino Acid

Colorless and odorless, glycine (or aminoacetic acid) is the simplest amino acid found in nature because of its single hydrogen side chain. But its functions are anything but simple: glycine is an essential component of protein synthesis, proper enzyme function, and lipid digestion and absorption.Wang2013

Glycine Glue: Collagen

Glycine is the primary amino acid in the most abundant protein in our bodies: collagen. You’ve probably heard of collagen; it’s referred to as the magical plumping agent to keep skin looking firm and healthy.

Collagen supports your bones, skin, hair, nails, and more, boosting recovery for sore joints and promoting a healthy gut.

Named after the Greek “kólla” meaning “glue,” collagen’s main function is to hold everything together.Lodish2000

Every third amino acid in collagen must be represented by a strong glycine molecule. If not, the tissue will be unstable. Imagine substituting the leg of a wooden chair with a piece of rolled up paper; the chair will probably collapse. Or maybe it’ll hold until you can trick your friend into trying it out. Either way, mutations resulting in a substitution of the strong glycine molecule can cause connective tissue disorders collectively referred to as brittle bone disease.Gajkogalicka2002

In addition to strength, glycine provides flexibility at enzymes’ active sites, allowing them to alter their conformation in order to bind with substrates.Yan1997

Essential Compounds

Glycine’s connections are particularly important for synthesizing essential compounds. Kind of like a recipe book. Combine glycine with arginine and a dash of methionine and you get the delicious creatine.Brosnan2011 It may not be food, but it is a form of fuel.

Most of your body’s creatine is stored in the muscles as phosphocreatine. Phosphocreatine assists with the production of the body’s stored energy, also known as ATP.Wyss2000 Creatine is a popular supplement choice among athletes because of its potential to increase energy production during high-intensity exercisePersky2001 or heavy lifting.Buford2007

A man doing a deadlift showing how glycine is a builder for creatine.

Glycine is one of the main ingredients in glutathione as well. Pair the amino acid with two others, cysteine and glutamate, and you get the non-protein tripeptide known for defending against oxidative stress.Lu2013 Glutathione is a powerful antioxidant your body makes to keep your free radical levels in check. Free radicals are basically free loaders—they take electrons from your cell membranes without your permission (called lipid peroxidation), which can weaken them. Weak cells from oxidative stress can weaken the immune system and contribute to diseases such as heart disease, diabetes, and cancer.Masella2005

Glycine as a Neurotransmitter

Glycine modulates both inhibitory neurotransmitters and excitatory neurotransmitters in the brain and the spinal cord, regulating reflex coordination, the processing of sensory information, and modulating the pain sensation.Zafra2008

The inhibitory functions of glycine are owed to the glycine-specific receptors in regions of the central nervous system,Betz2006 while the excitatory effects are facilitated by glutamate and the N-methyl-D-aspartate receptor.Johnson1997

Glycine Deficiency

Humans synthesize about 2.5g of glycine every day via serine hydroxymethyltransefrase. Despite being a great vocal warm up, this process doesn’t satisfy our daily 15g metabolic requirement for glycine.

Glycine is a conditionally-essential amino acid; we can survive on the small amount we create, but ideally, we’ll make up the deficit through our dietary choices or supplements. To be considered a non-essential amino acid, our ability to synthesize it would not be related to our dietary intake.

But why would we have such an imbalance between our glycine synthesis and our actual requirements? It may not be very efficient, but you can thank an evolutionary hiccup for this one.

When collagen first appeared as the most abundant protein in small animals, it was only required in amounts relative to size. Smaller animals, smaller needs.Cornishbowden2014 At that point, glycine synthesis was balanced.

As larger animals evolved, however, they inherited a regulatory system poorly suited to their higher collagen needs. Larger animals, larger needs, and an inability to synthesize enough glycine to satisfy them.

Let’s talk about those needs. Even though glycine is classified as only conditionally-essential, your joints might disagree. According to a meta-analyses of research studies identifying the relationship between collagen and bone health, the glycine-rich glue may increase bone mineral density and have a protective effect on cartilage around the joints.Porfirio2016 This posits collagen as playing a positive therapeutic role in osteoarthritis and osteoporosis. Best of all? The possibility to provide symptomatic relief from joint pain.Porfirio2016

Humans aren’t alone with their stunted synthesis of this (non)essential compound. Rhinos, elephants, fellow primates,Jurmain2000 and even our robust Neanderthal ancestorsStraus1957 share a common constraint: a proclivity toward developing osteoarthritis and other skeletal and joint diseases as we age.Greer1977 These developments may be a primary example of the Bruce Ames Triage Theory, which says that when access to nutrients is restricted, immediate survival is always prioritized over long-term health.Ames2006 It’s a sacrifice your body is willing to make.

According to this theory, micronutrient deficiencies could trigger responses that accelerate cancer and neural decay in exchange for maintaining immediate metabolic processes, like production of ATP.Ames2006 It’s kind of like choosing to eat that donut over a salad. Definitely a delicious choice in the moment, but the long-term effects are less sugar-coated. Eliminating a glycine constraint may have been a low-pressure evolutionary consideration compared to survival and reproduction processes. This was fine for your survival-driven ancestors, but modern humans are left with a chronic glycine deficit that may reduce collagen turnover and nonessential metabolic processes. Thanks, great-great-great-great-great grandparents.

Dietary Sources of Glycine

Collagenous proteins are the primary dietary source of glycine: bone broths, chicken and pork skins, egg whites, milk, and the aforementioned gelatin.Lodish2000 But loading up on all that protein won’t necessarily stimulate additional glycine synthesis.

Studies have found that the amino acid composition of the diet is more closely related to glycine production than protein intake. For example, a controlled dietary study of healthy participants found that reducing total protein intake didn’t have an effect on glycine synthesis. However, reducing the amounts of protein exclusively from the essential amino acids (such as histidine and lysine) led to significant reductions in glycine synthesis—a whopping 66%.Yu1985

Glycine and Cardiovascular Health

Not in love with glycine yet? This amino acid may already have your heart. Or at least the possibility of protecting it.

Heart Disease

Mounting evidence suggests that one of the benefits of glycine is assisting with your battle against heart disease. It has been studied to have numerous inverse associations with coronary risk factors relating to hypertensionElhafidi2006 and decreasing free fatty acids in animal models of disease.ElHafidi2004

Glycine may break down excess compounds associated with low-density lipoprotein formation.Ding2015

Low-density lipoproteins (LDLs) are the ones that float through your bloodstream and grab onto your arteries for dear life.

Over time, these LDLs accumulate, leaving your arteries clogged and struggling to function normally. Glycine availability may be able to modulate these LDLs to help protect against coronary artery disease.Ding2015

In a follow-up study of subjects with chest pains, higher glycine levels were associated with a lower risk of both heart disease and heart attacks. While this study does not suggest causality, it does motivate promising research into the mechanism by which glycine may positively affect heart health.Ding2015

Blood Pressure

If the potential for protection against heart disease doesn’t get your blood pumping, glycine won’t either. Or at least not in excess—glycine has been investigated for its ability to reduce blood pressure.ElHafidi2004

But the real pressure is figuring out how glycine is able to do this. It may be through glycine’s neurotransmitter activity, suggesting a reduction of heart rate when the sympathetic nervous system is activated.Talman1989 Or the reduction may be owed to glycine’s stimulation of fatty acid oxidation, which can reduce fat tissue accumulation.ElHafidi2004

Either way, lowering blood pressure is another powerful tool to protect against developing heart disease.

An illustration of the human body with a line connecting the heart and the brain, showing how glycine can reduce blood pressure.

Blood Glucose

Glycine has other business in your blood with its modulation of blood glucose levels. Despite being a sweetener, glycine has been researched for its ability to reduce blood sugar levels.

Post-meal blood sugar levels (also known as postprandial) may experience a reduction because of greater insulin secretion. Glycine has been observed for its ability to increase the release of a peptide that potentiates glucose-mediated insulin secretion when taken with meals.Gameiro2005 While more research in this area is needed, glycine treatment for type 2 diabetes is gaining momentum.

Glycine: The Sleeping Beauty of Amino Acids

Fixing your sleeping habits shouldn’t be just a fairytale. A good dose of glycine may transform hours of tossing and turning into a restful night’s sleep.

Falling Asleep

Glycine can have a cooling effect on your brain and body. Literally cooling—glycine ingestion has been associated with a decrease in your body’s core temperature, which is a natural accompaniment on its voyage to dreamland.Bannai2012

As body temperature declines, so does your heat production, followed by an increase in your heat loss. All three of these thermoregulation techniques are your body’s way of promoting sleep onset and slow brain wave activity. Conversely, your body’s core temperature begins to increase a few hours prior to waking.Colten2006

Glycine’s potential to assist with this thermoregulation may explain its link to a quickened ability to fall asleep.

In a study of subjects experiencing problems with falling asleep and dissatisfaction with sleep quality, ingesting a mere 3mg of glycine prior to bedtime was correlated with faster rates of sleep onset.Yamadera2007 In addition to this rapid REM reception, subjects also experienced shortened latency to reaching the deepest sleep stage without changing their sleep architecture.Yamadera2007

Your body is a skillful sleep architect—it plans and builds the ideal night of rest to rejuvenate you for the morning. The plan involves cycles of rapid eye movement (REM) sleep and (NREM) sleep correlated with different brain wave patterns and physiology, culminating in your unique slumber skyline.Colten2006

There are four stages of NREM sleep leading to REM sleep. REM sleep is the deepest stage of sleep you can thank for dreams. There’s no body movement during REM sleep. That’s because your body is protecting itself from physically reacting to your dreams.Colten2006 Imagine trying to actually fight off that hoard of zombies while you’re dreaming about them. It may not end well for you, the zombies, or the innocent lamp on your bedside table.

Unlike a real building, our unique cityscape snoozing is rather fragile. Disruptions in sleep architecture or irregular cycling is associated with sleep disorders.Colten2006

Waking Up

In a study on levels of glycine and sleep efficacy, researchers observed that glycine plays a significant role in alleviating symptoms of fatigue in people with poor sleep.Inagawa2006 Subjects reported positive effects on feelings of clear-headedness, liveliness, and self-assessed quality of sleep.Inagawa2006

A 2012 study echoed the findings, adding that glycine may be able to improve psychomotor vigilance the morning after ingestion.BannaiM2012 In this study, participants without sleep disturbances had their nightly naps cut by 25% to induce fatigue.

Fatigue met its match in glycine—participants reported significant decreases in sleepiness compared to the placebo while their testing performances soared.

This indicates that glycine may have practical implications for those with only occasional sleep restrictions in addition to those with sleep disorders.BannaiM2012

Those occasional nights of poor sleep deserve just as much attention as chronic disorders. Certain supplements combine the natural sleep hormone melatonin with stress-reducingKimura2007 L-theanine and morning-motivator glycineInagawa2006 to induce a high quality night of rest. In addition to falling asleep faster,Ferracioli2013 These products can help you get going the next day feeling fatigue-freeBannaiM2012 and ready to go.

An illustration of a thermometer, showing how glycine cools you down to help you sleep.

Supplementing with Glycine

If you’re ready to find a happily ever after with glycine, ensure you seek medical advice from your doctor before adding it as a daily supplement.

Clinical trials have dosed glycine up to 0.8g per kilograms of body weight in a healthy adult. For an adult weighing around 175 pounds, that’d be about 64 grams of glycine. Lower daily doses of 15g - 25g have been used in most studies,InagawaK2006 but glycine is generally well tolerated at relatively high doses (up to 90g).InagawaK2006

While no major adverse effects of glycine supplementation have been reported, mild side effects have been reported. Mild side effects include abdominal pain and soft stools, with abdominal pain generally reported when taking glycine on an empty stomach. Ingesting glycine during meals is not associated with causing daytime sleepiness.InagawaK2006

Give it a Rest

Whether you’re looking for a better night’s sleep to fuel long workdays or want to ensure you’re hitting your evolutionarily-stunted metabolic needs, glycine may be able to help you achieve your goals.

Along the way, this powerhouse amino acid may be able to offer protection against the atherosclerotic process to boost heart health. Another heart helper? Glycine’s promising modulations of blood glucose levels in normal adults and those with blood glucose sensitivity problems.

Even if you’re not a fan of love stories, rest assured that you and glycine could live happily ever after.

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