The key findings of this trial are that (1) compared to YAs, OA have GSH deficiency, elevated OxS, impaired MFO, higher inflammation, endothelial dysfunction, insulin resistance, muscle‐protein breakdown, elevated body fat and lower cognitive function, gait speed, muscle strength and exercise capacity, (2) supplementing GlyNAC as GSH precursors for 24‐weeks significantly improved these defects, and (3) accrued benefits receded on stopping GlyNAC for 12‐weeks. The gene discussed is INS; the disease is endothelial dysfunction.