Anyone who reads up on sleep comes across glycine sooner or later. There is nothing exotic about it: your body uses gram after gram of it every day, in skin, tendons and bone. Why sleep research of all fields is interested in it has to do with its many jobs.
The simplest amino acid there is
Glycine is the smallest of the twenty amino acids the body builds protein from. It fits into places where no other would. In collagen, the protein of skin and connective tissue, glycine sits at every third position. Without this tiny building block, the triple spiral of collagen could not fold at all.
Collagen makes up about a third of all the protein in the body. That puts glycine among the amino acids you need in the largest amounts.
What the body does with it
Glycine has several jobs at once:
- Building block of collagen, the material of connective tissue, skin and joints.
- Part of glutathione, one of the body's most important antioxidants. Glutathione is made of three amino acids, and one of them is glycine.
- Raw material for creatine, which muscle and nerve cells need for their energy.
- Messenger in the nervous system: in the spinal cord and brainstem, glycine dampens signals, much like GABA.
That last point gave researchers the idea that glycine might have something to do with sleep. Animal studies now point to a different route: block that dampening receptor and the effect stays the same. The trail leads to the brain region that runs the internal clock. What it looked like in people in the sleep laboratory, with electrodes on their heads and a placebo for comparison, is the subject of a separate article.
Non-essential does not mean unimportant
Glycine is classed as non-essential. That only means the body can make it itself, mainly from the amino acid serine. Whether it makes enough is another question.
That is exactly what the Spanish biochemist Enrique Meléndez-Hevia and his team worked out in 2009. For an adult weighing 70 kilos, they added up how much glycine the body makes, how much comes in with food and how much is used.
The body makes about 3 grams itself, and food supplies 1.5 to 3 grams. About 15 grams are needed, most of it for collagen. On paper, that leaves a gap of about 10 grams a day. Experts therefore sometimes call glycine conditionally essential.
The Norwegian Scientific Committee for Food and Environment (VKM) puts the body's own production higher, at about 8 grams, plus 3.2 grams from food on average. How big the gap is depends on whose calculation you follow.
Our daily dose is still 3 grams. The gap is a calculation for the whole body, mostly for building collagen. For sleep, what counts is the amount from the sleep studies, and in all three it was 3 grams in the evening.
Where glycine comes from
What the body does not make itself comes from food. Mostly from the parts of the animal that rarely end up on the plate today:
- Bone broth and gelatine: by far the richest sources
- Skin, cartilage and tendons: what used to go into the pot
- Meat and fish: much less, but regularly
- Pulses and seeds: plant sources in smaller amounts
If you only eat fillet and breast, you take in much less glycine than someone who also eats skin, cartilage and broth. Our grandparents still put all of that in the pot. How much is in gelatine, beef and tofu is shown in our table.
What glycine tastes like
Glycine tastes slightly sweet. That is where the name comes from: glykys is Greek for sweet. It is one of the reasons the food industry uses glycine.
Sources
- Meléndez-Hevia E, De Paz-Lugo P, Cornish-Bowden A, Cárdenas ML: A weak link in metabolism: the metabolic capacity for glycine biosynthesis does not satisfy the need for collagen synthesis. Journal of Biosciences, 2009, Volume 34, pages 853–872. To the study
- VKM (Norwegian Scientific Committee for Food and Environment): Risk assessment of "other substances" – glycine. VKM Report 2016:58. To the report
