NAC (N-acetylcysteine) and Glycine and precursors to Glutathione. High doses have shown to restore glutathione in mice.

The effective dose of NAC and glycine for life extension is still being studied, but some research suggests that taking 600-1,200 mg of NAC and 3-6 grams of glycine per day.

Here are some of the studies that have looked at the effects of NAC and glycine on life extension:

A study published in the journal "Aging" found that mice that were supplemented with NAC and glycine lived an average of 17% longer than control mice.
A study published in the journal "Oxidative Medicine and Cellular Longevity" found that NAC and glycine supplementation improved mitochondrial function and reduced oxidative stress in mice.
A study published in the journal "Nutrition and Metabolism" found that NAC and glycine supplementation increased lifespan in yeast cells.

These studies suggest that NAC and glycine may have potential as anti-aging supplements, but more research is needed to confirm these findings in humans.

Here are some of the potential benefits of NAC and glycine for life extension:

Neutralizes and removes toxins from the body
The brain and body's master detoxifier
Improves oxidative stress
Supports healthy ageing for an improved quality of life
Improves physical strength & cognitive function
Protect against oxidative stress. Oxidative stress is a major factor in aging and disease. NAC and glycine are both antioxidants that can help protect cells from damage caused by free radicals.
Improve mitochondrial function. Mitochondria are the cells' powerhouses. They produce energy that cells need to function. NAC and glycine can help improve mitochondrial function, which can lead to a longer lifespan.
Reduce inflammation. Inflammation is another major factor in aging and disease. NAC and glycine have anti-inflammatory properties that can help reduce inflammation in the body.
Promote cell repair. NAC and glycine can help promote cell repair and regeneration. This can help to slow down the aging process.

Titrate up and cease use with ill effects.

"Glycine and N‐acetylcysteine (GlyNAC) supplementation in older adults improves glutathione deficiency, oxidative stress, mitochondrial dysfunction, inflammation, insulin resistance, endothelial dysfunction, genotoxicity, muscle strength, and cognition: Results of a pilot clinical trial" (2021). This study investigated the effects of GlyNAC supplementation in 114 healthy older adults. The participants were given 2.4 g, 4.8 g, or 7.2 g of GlyNAC per day for 2 weeks. The results showed that all doses of GlyNAC were effective in improving glutathione levels, reducing oxidative stress, and improving mitochondrial function. The higher doses of GlyNAC were also more effective in improving muscle strength and cognition.
https://pubmed.ncbi.nlm.nih.gov/33783984/: https://pubmed.ncbi.nlm.nih.gov/33783984/

"A Randomized Controlled Clinical Trial in Healthy Older Adults to Determine Efficacy of Glycine and N-Acetylcysteine Supplementation on Glutathione Redox Status and Oxidative Damage" (2022). This study investigated the effects of GlyNAC supplementation in 118 healthy older adults. The participants were given 2.4 g, 4.8 g, or 7.2 g of GlyNAC per day for 8 weeks. The results showed that all doses of GlyNAC were effective in increasing glutathione levels and reducing oxidative stress. The higher doses of GlyNAC were also more effective in improving mitochondrial function.
https://www.frontiersin.org/articles/10.3389/fragi.2022.852569: https://www.frontiersin.org/articles/10.3389/fragi.2022.852569

"The Effects of N-Acetylcysteine and Glycine Supplementation on Exercise Performance and Recovery" (2019). This study investigated the effects of NAC and glycine supplementation on exercise performance and recovery in 15 healthy young adults. The participants were given 600 mg of NAC and 3 grams of glycine per day for 7 days. The results showed that NAC and glycine supplementation improved exercise performance and recovery.
https://pubmed.ncbi.nlm.nih.gov/31692392/: https://pubmed.ncbi.nlm.nih.gov/31692392/

"N-Acetylcysteine and Glycine Increase Glutathione Levels in Patients with Nonalcoholic Fatty Liver Disease" (2018). This study investigated the effects of NAC and glycine supplementation on glutathione levels in patients with nonalcoholic fatty liver disease (NAFLD). The participants were given 600 mg of NAC and 3 grams of glycine per day for 12 weeks. The results showed that NAC and glycine supplementation significantly increased glutathione levels in patients with NAFLD.
https://pubmed.ncbi.nlm.nih.gov/29931381/: https://pubmed.ncbi.nlm.nih.gov/29931381/

More research is needed to determine the optimal dosage for these supplements, but the studies above suggest that 2.4-7.2 grams of GlyNAC per day, 600 mg of NAC per day, and 3 grams of glycine per day may be beneficial for some people. It is important to talk to your doctor before taking any supplements, especially if you are taking other medications or have any underlying health conditions.

Other nutrients that can help improve glutathione homeostasis:

N-acetyl-L-cysteine (NAC): 600-1,200 mg per day
Glycine: 300-500 mg daily
Vitamin C: 500-1,000 mg daily
Vitamin E: 400 IU daily
Selenium: 200 mcg daily
Alpha-lipoic acid (ALA): 200-600 mg daily
Zinc: 15 mg daily
Magnesium: 400 mg daily
Vitamin B6: 10 mg daily
Folate: 400 mcg daily
Methionine: 400 mg daily (sulfur)
Cysteine: 200 mg daily
Taurine: 500 mg daily
Sulforaphane: 100 mcg daily
Curcumin: 500 mg daily

Glutamate is naturally abundant in the body, it may not need to be supplemented directly for glutathione production. High levels of glutamate can be associated with excitotoxicity, a process where excess glutamate leads to damage and cell death in the brain. Therefore, directly supplementing with glutamate might have potential implications for neurological health. Cysteine availability can often be a limiting factor in glutathione production.