Glycine is the smallest amino acid. Don’t let that fool you, though. Glycine may not be big and powerful all on its own, but it is extremely versatile, and it is particularly important to athletes for reasons beyond muscle repair. Glycine is one of three amino acids (along with proline and hydroxyproline) that are found in unusually large quantities in collagen. Collagen is the main protein in tendons, ligaments, skin, and pretty much every other tissue in the human body that is built to be resilient. After alanine and glutamine, glycine is a primary amino contributor to gluconeogenesis during exercise. Glycine obviously already has a lot going for itself, but one emerging area of research on glycine is extremely interesting, and that has to do with glycine’s role in mitochondrial health and aging.
There has only been one study on glycine as it pertains to endurance performance. A study in 1999 sought to evaluate the ergogenic effects of arginine and used glycine as the placebo. However, the group supplementing glycine had better marathon times that reached statistical significance. This was a surprise to the researchers who expected no difference in performance. There are a number of methodological flaws to the study, but it is the only direct evaluation of glycine supplementation for exercise performance, and it appears fairly promising.
Endurance performance is largely based on our cells’ mitochondria. Mitochondria are the “powerhouses” of the cell, which means they make most of our bodies’ energy through a process called respiration. This is not news, but in case you’re unaware, running, cycling, swimming, etc. requires HEAPS of energy (ATP). For events that are not even very long (~3+ minutes) most ATP is produced in the mitochondria. The importance of mitochondria are highlighted by the observations that individuals with mitochondrial myopathies have only 50% the endurance capacity of sedentary, but otherwise healthy, individuals. Peak oxygen consumption for those with mitochondrial impairments is only 16 mL per kg per minute vs. 32 in sedentary controls and greater than 65 in well-trained athletes (the highest ever recorded are in the 90’s, typically by “whole-body” endurance athletes, like skiers).
Glycine and the Mitochondria
A prevailing theory of aging has to do with epigenetics. Epigenetics is the study of gene expression – the relationship of which genes are active or inactive and the magnitude of their activity. As we age, genetic expression changes, which causes the unwanted “side effects” of getting older. Removing or reversing the changes in genetic expression to revert them back to a “young” state is the objective of current investigations, particularly in the mitochondria. Mitochondrial targets are of interest because mitochondria produce free radicals (they just do, it’s unavoidable). The free radicals end up damaging DNA and altering mitochondrial function, which affects energy balance and availability.
While energy cannot fully explain aging, reversing mitochondrial decline is one major step in the process, and mitochondrial health is entirely too important for athletes to be ignored. The number and activity of mitochondria diminish with age. Some of the key processes affected are glycine synthesis and degradation. Scientists examining fibroblasts from both young and elderly participants first confirmed differences present between the aged and young cells prior to reprogramming the elderly cells. Reprogramming the cells reversed age-associated declines in cellular respiration.
When looking for genes to explain the observed effects, the authors identified GCAT and SHMT2. These two genes control glycine production, and aging resulted in less glycine in aged cells than young cells. To confirm that it was indeed glycine that mediated the observed “aging,” glycine was added to the media (water) of some elderly fibroblasts, and the addition of glycine restored the elderly cells respiration to the levels of the young cells.
One of the ways that glycine may be exerting its effects is through Sirtuin proteins. Sirtuins, of which there are many, respond to a modified form of vitamin B3 (NAD) and also express a preference for glycine. Sirtuins participate in DNA repair (such as DNA damaged by free radicals), restoring proper DNA function. The associations of sirtuins and aging come from research on sirtuin activators. One pharmaceutical sirtuin activator increased the lifespan of mice by 11 – 44% between a low and high dose of the drug. Furthermore, genetically-augmented mice bred to lack sirtuins display premature, degenerative aging.
There’s a lot of cool evidence surrounding glycine and aging and even athletic performance. However, it’s too soon to say how much this can actually have an impact on our lives, as fun as it is to speculate. On the other hand, there’s no real downside to adding glycine, it’s fairly inexpensive and it does seem to have a defined role in mitochondrial health. Thus, in addition to being converted to pyruvate for ATP production and forming very important collagen proteins, glycine might actually aid mitochondrial functioning.
The athletes consuming glycine before their marathon were consuming 10g per day, and only ~4 grams per day would be necessary to increase plasma levels of glycine to that of the fibroblast study, so perhaps the surprise of the researchers can be explained by an impact of glycine on the mitochondria having a subsequent effect on respiration and improved endurance for runners.
For all of these reasons (and because it’s fun to write optimistically speculative articles), 400mg of glycine are contained in each serving of SustainElite. We primarily want to feed ATP production from all angles and prevent cannibalization of muscle tissue (discussed in the alanine and glutamine articles), but we couldn’t say no to including glycine. We asked ourselves if this would help make SustainElite the best carbohydrate-electrolyte drink available, and the answer was yes. Being more than just a carbon backbone for ATP production, glycine definitely fits the bill.
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