Your body produces it and recycles it, and your day to day status depends heavily on your overall nutrition and your oxidative stress load
Adv Nutr 5:394403 Calabrese V, Scapagnini G, Ravagna A, Bella R, Butterfield DA, Calvani M, Pennisi G, Giuffrida Stella AM (2003) Disruption of thiol homeostasis and nitrosative stress in the cerebrospinal fluid of patients with active multiple sclerosis: evidence for a protective role of acetylcarnitine
What happens if that number rises to 10%, 25%, 50% or more over the next 5, 10, 25 years
What Glutamine supplements can do According to a study published by the International Journal of Molecular Sciences, In gut physiology, glutamine promotes enterocyte proliferation, regulates tight junction proteins, suppresses pro-inflammatory signaling pathways, and protects cells against apoptosis and cellular stresses during normal and pathologic conditions. The authors also note that: As glutamine stores are depleted during severe metabolic stress including trauma, sepsis, and inflammatory bowel diseases, glutamine supplementation has been examined in patients to improve their clinical outcomes. Naturally occurring glutamine in the body works to protect the intestine so it makes perfect sense that a supplement would also increase intestinal stability