I am always careful with NAC. It is such a powerful antioxidant is it possible it could inhibit ROS signalling, which is a very important part of many chemical pathways?
You ended what I felt was a statment rather than question with a question mark.
Because NAC is not normally needed by healthy people, daily recommended allowances have yet to be established. However, most of the research on NAC has used dosages ranging from 250 milligrams to 1,250 milligrams per day.
One study published in the early 1980s found that people taking oral doses of n-acetyl cysteine experienced side-effects such as nausea, vomiting and headaches, but these symptoms have not been reported consistently in other studies. Another study published in 1992 found that large amounts of cysteine could cause damage to nerve cells and increased oxidative stress (what I believe you are referencing but I could be wrong) - but this has yet to be replicated to the best of my knowledge and with doses higher than 1200 mg daily and we also have to discuss what it means to induce high levels of oxidative stress (like those with intense exercise; defined differently in some instances than you might think).
Furthermore, supplementation of NAC at low concentrations (600 mg) per day for 14 weeks reduced superoxide radicals and improved glutathione peroxidase in healthy volunteers, while a high dose at 1,200 mg per day significantly reduced hydrogen peroxide (H[SUB]
2[/SUB]O[SUB]
2[/SUB]) in COPD patients. Does that translate to the normal population or exercise enthusiasts? Well, I don't know exactly - but there is positive data on 600mg with sperm in hypogonadal men; there is positive data on NAC inhibiting muscle fatigue; there's good data on stresses of the liver and glycemic control (of which; most multiple meal bodybuilders use).
The muscle fatigue concept is interesting because it probably gets us closest to the bottom line of what is happening in side effect PRO-oxidation states in that NAC inhibits fatigue in a time- and dose-dependent manner. Plasma NAC and cysteine concentration peak within 60–120min after ingestion. Although the bioavailability of orally administered NAC is low, oral administration of 150 mg/kg NAC solution increased plasma NAC concentration by 20- to 30-fold, and plasma cysteine concentration by 10- to 15-fold. A similar dose administered via intravenous infusion yielded plasma NAC concentrations an order of magnitude higher. Both routes of administration inhibited oxidation of circulating glutathione during exercise to a similar degree. This “ceiling effect” of NAC may be a consequence of glutathione regulation ofglutathione synthesis through a negative feedback mechanism.
My biggest concern is how many people do not realize the micronutrient implications (which are easily enough accounted for, but most do in fact screw it up). NAC may increase urinary zinc excretion; as a result, people taking n-acetyl cysteine for long periods of time should also increase their intake of zinc and copper (AT DIFFERENT TIMES OF DAY).
This leads to my recommendations based on copious tallies of research which probably means that too much NAC in the acute setting (like most things even Vitamin C) has an upper limit. The single-dose limit on Vitamin C I use with clients is 500mg in a single sitting (max 5-6 times per day); the single-dose limit on NAC I use with clients is 600mg in a single sitting (max 1-2 times per day based on quality research of potential toxicity).
