Surprised i haven't seen this before but it is really interesting. Sorry if its been posted before i only had a quick look though the previous posts.
https://academic.oup...4/3/847/4431102
Deficient synthesis of glutathione underlies oxidative stress in aging and can be corrected by dietary cysteine and glycine supplementation
"Glutathione deficiency in elderly humans occurs because of a marked reduction in synthesis. Dietary supplementation with the glutathione precursors cysteine and glycine fully restores glutathione synthesis and concentrations and lowers levels of oxidative stress and oxidant damages. These findings suggest a practical and effective approach to decreasing oxidative stress in aging."
Glutothione in red blood cells was dramatically increased and levels of oxidants such as lipid peroxides were brought down impressively.
Unless i calculated wrong, it takes around 8 grams of glycine (also cysteine, didnt look into how much) to get these effects.
Glycine really does seem to be quite a fascinating substance for anti-aging. Considering that it appears to be a rate limiting factor for glutathione AND collagen synthesis, has the potential to extend lifespan and lowers oxidative stress in the elderly. .
Definitely going to start mixing some in with the collagen i already take, around 8g .
This is an interesting paper. I've been taking ~15g glycine per day and ~2g NAC per day for a while, mainly for glutathione status.
This paper suggests 8g/day of glycine and 10.5g/day of NAC. The dosage of NAC seems excessive, although the patients were elderly, as opposed to the paper I point out below, which used 1.8g/day of NAC for 4 weeks as a treatment for hypertension in middle aged patients (but also increased the GSH:GSSG ratio significantly
https://www.ncbi.nlm...pubmed/26447155
ABSTRACT
Background: Elevated total plasma homocysteine (tHcy) is considered to be an independent cardiovascular disease risk factor, although tHcy lowering by B-vitamins improves only certain clinical endpoints. N-acetylcysteine (NAC), a thiol-containing antioxidant, acutely lowers tHcy and possibly also blood pressure. However, to our knowledge, at present no conclusive long-term evaluation exists that controls for factors such as hyperlipidemia, smoking, medication, and disease stage, all of which affect the thiol redox state, including tHcy. Objective: We reanalyzed 2 double-blind, placebo-controlled trials in unmedicated middle-aged men, one in a hyperlipidemic group (HYL group; n = 40) and one in a normolipidemic group (NOL group; n = 42), each stratified for smokers and nonsmokers.
Design: We evaluated the effect of 4 wk of oral NAC (1.8 g/d) on tHcy (primary endpoint), plasma thiol (cysteine), and intracellular glutathione concentrations as well as on blood pressure. The HYL group had total cholesterol .220 mg/dL or triglycerides .150 mg/dL.
Results: NAC treatment significantly (P = 0.001, multivariate analysis of variance for repeated measures) lowered postabsorptive plasma concentrations of tHcy by 211.7% 6 3.0% (placebo: 4.1% 6 3.6%) while increasing those of cysteine by 28.1% 6 5.7% (placebo: 4.0% 6 3.4%) with no significant impact of hyperlipidemia or smoking. Moreover, NAC significantly decreased systolic (P = 0.003) and diastolic (P = 0.017) blood pressure within all subjects with a significant reduction in diastolic pressure in the HYL group (P = 0.008) but not in the NOL group. An explorative stepwise multiple regression analysis identified 1) post-treatment cysteine as well as 2) pretreatment tHcy and 3) albumin plasma concentrations as being significant contributors to tHcy reduction.
Conclusions: Four weeks of oral NAC treatment significantly decreased plasma tHcy concentrations, irrespective of lipid or smoking status, and lowered systolic blood pressure in both normolipidemic and hyperlipidemic men, with significant diastolic blood pressure reductions in the HYL group only. Increased oral intake of cysteine may therefore be considered for primary or secondary prevention of vascular events with regard to the 2 independent risk factors of hyperhomocysteinemia and arterial hypertension.
It seems clear that cysteine is the limiting factor in glutathione synthesis (especially considering that it exists in MUCH lower concentrations than glycine in the blood). However given that we know that glycine (despite it's abundance in the blood), is insufficient in humans for collagen synthesis, it may also be a limiting factor for making glutathione in some circumstances, i.e. when there are demands for it elsewhere. Here is a good example, where children experiencing catch-up growth after malnutrition no longer had enough glycine for glutathione synthesis:
https://www.academia...emental_Glycine
Conclusion: it is advisable for take both NAC and Glycine. NAC for glutathione and Glycine for collagen, and glutathione in some demanding circumstances.
I take them in the day, once I've broken my fast. On workout days I tend o use Whey instead of NAC (also a good source of cysteine), but without the direct anti-oxidative effects that might (if taken close to a workout) impede the damage required for muscle development.