Glycine: Collagen, Creatine, Sleep Trials and Indian Food Sources

Glycine is a non-essential amino acid: your body makes it, mostly from another amino acid called serine, so ICMR-NIN sets no daily requirement for it. It forms about a third of collagen, the protein of skin, bone and tendon, and it is one of the raw materials for creatine and glutathione. One published estimate puts the body's own output at about 3 g a day, with an ordinary diet adding 1.5 to 3 g. A few very small trials suggest that 3 g at bedtime may improve sleep. This entry belongs to the proteins and amino acids section.

What is glycine, and what does it do?

Glycine is one of the twenty amino acids that make up body protein. ICMR-NIN's Dietary Guidelines for Indians, 2024, name nine as essential because they are not synthesised in the body, and say the remaining ones can be. Glycine is in the second group. A 2013 review in the journal Amino Acids describes it as synthesised from serine, threonine, choline and hydroxyproline, mainly through the liver and kidneys.

Its uses go well beyond filling a place in protein chains. The same review lists glycine as a building block for glutathione, haem, creatine, nucleic acids and uric acid, and as a component of the bile acids that help you digest fat and absorb long-chain fatty acids. It also acts in the nervous system. Collagen is the largest single call on the supply: a 2019 review in the journal Molecules gives glycine as 33 per cent of the collagen molecule.

How much glycine do you need?

No requirement has been set by ICMR-NIN, WHO or any body this entry could find, because glycine is classed as non-essential. What exists is a pair of estimates. A 2009 paper in the Journal of Biosciences added up the reported routes and put the body's synthesis at about 3 g a day, more than 85 per cent of it from serine, and intake from an ordinary diet at 1.5 to 3.0 g a day. Its authors argue that this falls short of what a 70 kg adult uses by about 10 g a day, and call glycine semi-essential.

That shortfall is a calculation, not a measured deficiency, and other researchers read the same biochemistry differently: a 2011 paper on creatine in Amino Acids describes glycine as readily synthesised in adults. The requirement that is settled is the one for protein. ICMR-NIN's 2020 allowance is 0.83 g per kg of body weight a day, 54 g for a 65 kg man and about 46 g for a 55 kg woman. The protein calculator gives your own figure.

The Indian position: silence from ICMR-NIN and a place in FSSAI's schedule

ICMR-NIN's amino acid pattern, printed as Table 8.2 of the 2024 guidelines, has rows only for the essential amino acids, for example 45 mg per gram of protein for lysine, explained in the entry on lysine. Glycine does not appear. The guidelines' message on supplements is a general one: protein in the form of supplement powders is not advisable in high amounts, and a balanced diet with good-quality protein foods is preferred to any single nutrient taken as a supplement.

FSSAI does name it. Glycine is entry (vi) under non-essential amino acids in Schedule II of the health supplement and nutraceutical regulations, the list of amino acids a health supplement may contain. No quantity is printed beside it. A glycine product sold as a health supplement has to say HEALTH SUPPLEMENT on the pack, declare how much glycine a serving holds, carry the advisory NOT FOR MEDICINAL USE and state that it does not replace a varied diet. The regulations bar any claim that a health supplement prevents, treats or cures a human disease, which rules out selling glycine as a remedy for insomnia.

Glycine in Indian foods

Every protein food carries glycine, and the differences between foods are smaller than supplement marketing suggests. The Indian Food Composition Tables 2017 give it in grams per 100 g of protein. Milk protein is at the low end, 2.35 for cow's milk and 2.18 for paneer. Dals sit between 3.2 and 3.9, rice at 4.18 and atta at 3.76. Nuts and oilseeds are higher, 5.56 for groundnut and 6.32 for white sesame, and amaranth seed, sold as rajgira, reaches 8.50. Chicken and goat muscle run from about 4.8 to 6, and cuts rich in connective tissue go higher: 8.20 for goat tripe against 5.64 for goat leg.

Because the share varies so little among plant foods, the amount of glycine you eat mostly tracks the amount of protein you eat. NNWA's table of protein in Indian foods ranks the whole database, and the page on amaranth seed gives the full panel for the grain with the most glycine. IFCT 2017 does not report collagen or gelatin, so there is no Indian figure for paya, bone broth or fish skin.

Why does glycine matter for collagen, creatine and glutathione?

Because all three are built from it, and the body makes each of them continuously. Collagen is one third glycine, which is why collagen powders are in effect a glycine-rich protein; the entry on collagen explains why that does not make them a complete protein. Creatine is assembled from glycine, arginine and methionine. The 2011 paper in Amino Acids puts the daily loss of creatine at about 2 g in 70 kg men aged 20 to 39, about half of which meat and fish can replace in people who eat them, while vegetarians make virtually all of it.

The same paper concludes that creatine synthesis is not a major burden on glycine, since glycine is easily made; the strain falls on methionine and arginine. The entry on creatine covers the supplement. Glutathione, the cell's own antioxidant, needs glycine and cysteine. In a study of 8 older and 8 younger adults in the American Journal of Clinical Nutrition, the older group had lower red-cell glycine and glutathione, and two weeks of cysteine and glycine together raised their glutathione concentration by 94.6 per cent.

A later placebo-controlled trial from the same group gave glycine with N-acetylcysteine to 12 older adults for 16 weeks, with 12 on placebo, and reported better glutathione levels and several other measures. Both studies are small, both gave glycine alongside a cysteine source, and neither shows what glycine alone would do.

Does glycine help you sleep?

Possibly, but the trials are too small to settle it. A 2024 systematic review in GeroScience covered 50 studies of glycine in adults. In healthy people it found three trials of 3 g taken 30 minutes to an hour before bed, lasting two to four nights, with 10, 11 and 19 participants. They reported better sleep quality and less fatigue and sleepiness the next day. The reviewers' verdict was that these studies had small sample sizes with a high risk of bias.

One of the three shows the problem. Published in Frontiers in Neurology in 2012, it recruited ten healthy men, all employees of the food company whose laboratory ran the study, cut their sleep by a quarter for three nights and measured how tired they felt. Seven were analysed. Fatigue scores improved; sleepiness showed only a tendency to improve. No large, independent trial has followed. The handbook's entry on melatonin covers the better-studied sleep supplement.

Can you have too little glycine?

No deficiency disease from a low glycine intake has been described in the sources read for this entry, and the body's own synthesis means a healthy adult does not depend on food for it. The argument that supply runs short rests on the calculation described above, and on findings such as lower red-cell glycine in the eight older adults of the American study. Neither amounts to a diagnosis. In India the practical risk is the familiar one: a diet short of total protein or of quality protein. Fix that with dal, milk, curd, egg or meat, and glycine comes along with it.

A worked example: a vegetarian teacher's day

This is an illustrative case, not a real person. A 34-year-old vegetarian school teacher in Chennai weighs 55 kg and has read that vegetarians miss out on glycine because they eat no collagen. Her usual day has 200 g of rice, rotis from 75 g of atta, 60 g of toor dal across sambar and dal, 30 g of moong dal, 300 g of milk and curd counted as milk, and 30 g of groundnuts.

Common mistakes and myths about glycine

The commonest mistake is to treat glycine as something only animal foods supply. Collagen itself is found only in animal tissue, but glycine is in every protein, and groundnut, sesame and rajgira protein carry about as much of it per gram as meat protein does in IFCT 2017. A second mistake is to read the 10 g shortfall as a requirement. It is one research group's estimate, and no guideline body has adopted it.

A third mistake is to count free glycine on a protein powder's label as protein. NNWA's article on whether you need protein powder covers how to read a powder's label. The last is to expect a sleep supplement to repair what late screens, caffeine and short nights have undone.

Glycine supplements: safety, side effects and when to see a doctor

The amounts used in the sleep trials were small and taken for a few nights only, so they say little about long-term use. The GeroScience review found that negative effects were reported mainly where a large amount was given at once: single intakes of 0.8 g per kg of body weight, about 44 g for a 55 kg adult, had negative effects on sensorimotor gating, a measure of how the brain filters sensation, and on cognitive performance in healthy volunteers. Much of the remaining research is in psychiatric patients under specialist care, which is no model for self-treatment. This entry gives no dose.

See a doctor if you sleep badly most nights for a month, if you snore heavily and wake unrefreshed, or if low mood or anxiety comes with the sleeplessness. Stop a supplement that makes you feel sick or drowsy by day and seek advice. Never stop or alter a prescribed medicine in order to try an amino acid in its place.

Learning about amino acids at NNWA

The Certification in Nutrition introduces proteins and amino acids, and the Diploma in Nutrition takes them further. Both are run by NNWA, a private skill academy based in Kolkata, with classes held online in English and Hindi. They prepare people to coach healthy clients and to refer anyone with a medical condition to a doctor. Neither course is a degree or a dietitian qualification.