Ascorbic acid oxidating
A meta-analysis of 44 clinical trials has shown a significant positive effect of vitamin C on endothelial function when taken at doses greater than 500 mg per day.
The researchers noted that the effect of vitamin C supplementation appeared to be dependent on health status, with stronger effects in those at higher cardiovascular disease risk.
The amount was chosen because human trials had reported diarrhea and other gastrointestinal disturbances at intakes of greater than 3,000 mg/day.
This was the Lowest-Observed-Adverse-Effect Level (LOAEL), meaning that other adverse effects were observed at higher intakes.
The signs and symptoms in adults were nausea, vomiting, diarrhea, flushing of the face, headache, fatigue and disturbed sleep.
The main toxic reactions in the infants were skin rashes.
In humans, vitamin C is essential to a healthy diet as well as being a highly effective antioxidant, acting to lessen oxidative stress; a substrate for ascorbate peroxidase in plants (APX is plant specific enzyme); Ascorbate is required for a range of essential metabolic reactions in all animals and plants.
It is made internally by almost all organisms; the main exceptions are most bats, all guinea pigs, capybaras, and the Haplorrhini (one of the two major primate suborders, consisting of tarsiers, monkeys, and humans and other apes).
Although the results in humans were not statistically significant, this study is often cited as evidence that high doses of Vitamin C have an adverse effect on exercise performance.
In rats, it was shown that the additional Vitamin C resulted in lowered mitochondria production.
Since rats are able to produce all of their needed Vitamin C, however, it is questionable whether they offer a relevant model of human physiological processes in this regard.
A cancer-causing mechanism of hexavalent chromium may be triggered by vitamin C.
(the dose that will kill 50% of a population) in rats is generally accepted to be 11.9 grams per kilogram of body weight when given by forced gavage (orally).
In a group of spontaneously aborting women at the end of the first trimester, the mean values of vitamin C were significantly higher in the aborting group.