Dietary glycine can be rate-limiting for glutathione synthesis in normally fed humans. Glycine is a nonessential amino acid that can be synthesized from other substrates, but the amounts of glycine provided by some common diets is limiting for the synthesis of glutathione. Likely, supplemental glycine should have its largest impact on glutathione levels in those who consume diets relatively low in protein, notably vegetarians and vegans.
Availability of the amino acid cysteine is also known to be rate-limiting for the synthesis of glutathione, and it is well documented, both clinically and in animal studies, that cysteine supplementation-most practically achieved by administration of N-acetylcysteine (NAC)-can boost glutathione synthesis and levels.
A pilot human clinical trial conducted by researchers at Baylor College of Medicine reveals that supplementation with GlyNAC - a combination of glycine and N-acetylcysteine as precursors of the natural antioxidant glutathione - could improve many age-associated defects in older humans to improve muscle strength and cognition, and promote healthy aging.
Published in the journal Clinical and Translational Medicine, the results of this study show that older humans taking GlyNAC for 24 weeks saw improvements in many characteristic defects of aging, including glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, body fat, genomic toxicity, muscle strength, gait speed, exercise capacity and cognitive function. The benefits declined after stopping supplementation for 12 weeks. GlyNAC supplementation was well tolerated during the study period.
So... why not simply supplement with glutathione? One reason is that the bioavailability of glutathione is suboptimal. Another reason is that the 2 components, glycine and n-acetylcysteine, offer exciting benefits on their own. Glycine has shown to improve metabolic syndrome, is anti-inflammatory, and improves sleep quality. Glycine is the major inhibitory neurotransmitter in the brainstem and spinal cord, where it participates in a variety of motor and sensory functions. Glycine is also present in the forebrain, where it has recently been shown to function as a co-agonist at the N-methyl-D-aspartate (NMDA) subtype of glutamate receptor.
N-acetylcysteine is a powerful antioxidant and also improves insulin sensitivity, and in animal and in-vitro studies, n-acetylcysteine has shown to inhibit cancer proliferation.
Contact our office to learn about appropriate dosing of these supplements, based on clinical trials.